Database Management SystemsCursors

Cursors in SQL

LevelAdvanced

Duration90 mins

TopicCursors

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Cursor Types

Choosing the Right Cursor for the Job

Not all cursors are created equal. The type of cursor you choose fundamentally affects:

What you see: Does the cursor show a frozen snapshot or live data?
How you navigate: Can you scroll backward or only forward?
Resource consumption: How much memory and I/O does it require?
Concurrency behavior: How does it interact with other transactions?
Update capability: Can you modify data through the cursor?

Choosing the wrong cursor type leads to problems: static cursors on massive result sets exhaust memory; dynamic cursors on complex queries kill performance; forward-only cursors fail when you need random access.

This page provides deep understanding of cursor types across database platforms. While terminology varies (SQL Server uses STATIC/KEYSET/DYNAMIC; standard SQL uses INSENSITIVE/SENSITIVE), the underlying concepts apply universally.

What You Will Learn

By the end of this page, you will understand all major cursor types: Static (Insensitive), Keyset-driven, Dynamic (Sensitive), and Fast Forward-Only. You'll know their internal implementation, behavior characteristics, performance profiles, and when to use each. You'll be able to select the optimal cursor type for any scenario.

Cursor Type Classification

Cursor types are classified along two primary dimensions:

1. Sensitivity: Does the cursor see changes made to underlying data after it opens?

Insensitive (Static): Sees snapshot at OPEN time only
Sensitive (Dynamic): Sees all changes in real-time
Keyset: Hybrid—membership frozen, values current

2. Scrollability: What navigation directions are supported?

Forward-only: FETCH NEXT only
Scrollable: FETCH in any direction (NEXT, PRIOR, FIRST, LAST, ABSOLUTE, RELATIVE)

These dimensions combine to create practical cursor types:

Cursor Type Matrix
Type	Sensitivity	Scrollability	Memory	Sees INSERTs	Sees UPDATEs	Sees DELETEs
STATIC	Insensitive	Scrollable	High	No	No	No
KEYSET	Partial	Scrollable	Moderate	No	Yes	Detected
DYNAMIC	Sensitive	Scrollable*	Low	Yes	Yes	Yes
FAST_FORWARD	Asensitive	Forward-only	Minimal	Varies	Varies	Varies
FORWARD_ONLY	Typically Dynamic	Forward-only	Low	Yes	Yes	Yes

Converting Mermaid diagram...

SQL Server Terminology vs. Standard SQL:

SQL Server	Standard SQL	Description
STATIC	INSENSITIVE	Snapshot isolation
DYNAMIC	SENSITIVE	Real-time view
KEYSET	(no equivalent)	Key-driven hybrid
FAST_FORWARD	(optimization)	Optimized forward-only read-only

Default Behavior Varies

When you don't specify a type, the database chooses based on query characteristics and internal heuristics. This default (ASENSITIVE in standard SQL) means behavior may vary between statements and shouldn't be relied upon for critical code. Always explicitly specify your cursor type.

Static (Insensitive) Cursors

A static cursor creates a complete snapshot of the result set at OPEN time. This snapshot is stored in a temporary work area (tempdb in SQL Server, work tables in Oracle). All subsequent operations work with this copy, completely isolated from changes to the base tables.

Declaration:

-- SQL Server
DECLARE my_cursor CURSOR STATIC FOR
    SELECT * FROM orders WHERE status = 'pending';

-- Standard SQL
DECLARE my_cursor INSENSITIVE CURSOR FOR
    SELECT * FROM orders WHERE status = 'pending';

Converting Mermaid diagram...

Static Cursor Characteristics:

Static Cursor Behavior

•Complete Isolation: No visibility to concurrent INSERTs, UPDATEs, or DELETEs
•Scrollable: Supports all FETCH directions (NEXT, PRIOR, FIRST, LAST, ABSOLUTE, RELATIVE)
•Consistent Iteration: Row count and values remain constant throughout cursor lifetime
•Memory Intensive: Entire result set copied to temporary storage
•No Positioned Updates: Cannot use WHERE CURRENT OF (working on copy, not original)
•OPEN is expensive: Time to copy scales with result set size

static_cursor_example.sql
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-- Static cursor for consistent reporting
DECLARE @product_id INT, @product_name VARCHAR(100), @stock INT;
DECLARE @total_products INT = 0;
DECLARE @low_stock_count INT = 0;
 
DECLARE inventory_report CURSOR STATIC FOR
    SELECT product_id, product_name, stock_level
    FROM inventory
    WHERE warehouse_id = 1
    ORDER BY product_name;
 
OPEN inventory_report;
 
-- Even if another user modifies inventory during this loop,
-- we see a consistent snapshot
FETCH NEXT FROM inventory_report INTO @product_id, @product_name, @stock;
 
WHILE @@FETCH_STATUS = 0
BEGIN
    SET @total_products = @total_products + 1;
    
    IF @stock < 10
        SET @low_stock_count = @low_stock_count + 1;
    
    -- All logic based on consistent data
    PRINT @product_name + ': ' + CAST(@stock AS VARCHAR) + ' units';
    
    FETCH NEXT FROM inventory_report INTO @product_id, @product_name, @stock;
END
 
-- Report totals are consistent with detail rows
PRINT 'Total Products: ' + CAST(@total_products AS VARCHAR);
PRINT 'Low Stock Items: ' + CAST(@low_stock_count AS VARCHAR);
 
CLOSE inventory_report;
DEALLOCATE inventory_report;
 
-- Demonstration of scrollability
DECLARE scroll_demo CURSOR STATIC SCROLL FOR
    SELECT employee_id, hire_date
    FROM employees
    ORDER BY hire_date;
 
OPEN scroll_demo;
 
-- Jump to 10th employee
FETCH ABSOLUTE 10 FROM scroll_demo INTO @emp_id, @date;
PRINT '10th hired: Employee ' + CAST(@emp_id AS VARCHAR);
 
-- Jump to last employee
FETCH LAST FROM scroll_demo INTO @emp_id, @date;
PRINT 'Most recent: Employee ' + CAST(@emp_id AS VARCHAR);
 
-- Go back 5 positions
FETCH RELATIVE -5 FROM scroll_demo INTO @emp_id, @date;
PRINT '5 from end: Employee ' + CAST(@emp_id AS VARCHAR);
 
CLOSE scroll_demo;
DEALLOCATE scroll_demo;

When to Use Static

•Report generation requiring consistency
•Result sets that fit comfortably in memory
•Need for bidirectional navigation
•Calculations that must not be affected by concurrent changes
•Data export/archival processes

When to Avoid Static

•Very large result sets (memory pressure)
•Need to see real-time data changes
•Positioned UPDATE/DELETE required
•Long-running processes on busy tables
•When copy overhead exceeds benefit

Memory Consumption Alert

A static cursor on a query returning 1 million rows copies all 1 million rows to temporary storage at OPEN time. For wide rows (many columns, large strings), this can consume gigabytes of temp space. Monitor tempdb usage and set appropriate limits.

Dynamic (Sensitive) Cursors

A dynamic cursor provides a real-time view of the underlying data. It doesn't materialize a copy—instead, each FETCH operation directly accesses the base tables. This means all concurrent changes (INSERTs, UPDATEs, DELETEs) are immediately visible.

Declaration:

-- SQL Server
DECLARE my_cursor CURSOR DYNAMIC FOR
    SELECT * FROM orders WHERE status = 'pending';

-- Standard SQL
DECLARE my_cursor SENSITIVE CURSOR FOR
    SELECT * FROM orders WHERE status = 'pending';

Converting Mermaid diagram...

Dynamic Cursor Characteristics:

Dynamic Cursor Behavior

•Full Sensitivity: Sees all INSERTs, UPDATEs, and DELETEs in real-time
•Phantom Rows: New rows matching criteria can appear during iteration
•Disappearing Rows: Rows can vanish if deleted or modified to not match criteria
•Low Memory: No result set copy—points directly to tables
•Higher I/O: Each FETCH may require table access
•Positioned Updates Supported: Can use WHERE CURRENT OF
•Limited Scrollability: Some platforms restrict PRIOR/ABSOLUTE operations

dynamic_cursor_example.sql
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-- Dynamic cursor for real-time monitoring
-- Scenario: Process pending orders, seeing new ones as they arrive
 
DECLARE @order_id INT, @customer_id INT, @total DECIMAL(10,2);
DECLARE @processed_count INT = 0;
DECLARE @max_to_process INT = 1000;  -- Safety limit
 
DECLARE pending_orders CURSOR DYNAMIC FOR
    SELECT order_id, customer_id, total_amount
    FROM orders
    WHERE status = 'pending'
    ORDER BY order_date;
 
OPEN pending_orders;
 
FETCH NEXT FROM pending_orders INTO @order_id, @customer_id, @total;
 
WHILE @@FETCH_STATUS = 0 AND @processed_count < @max_to_process
BEGIN
    -- Process this order
    BEGIN TRY
        EXEC dbo.ProcessSingleOrder @order_id;
        
        -- Mark as processed (this UPDATE is visible to cursor!)
        UPDATE orders SET status = 'processed' WHERE order_id = @order_id;
        
        SET @processed_count = @processed_count + 1;
    END TRY
    BEGIN CATCH
        -- Handle error, order remains pending
        PRINT 'Failed to process order ' + CAST(@order_id AS VARCHAR);
    END CATCH
    
    -- IMPORTANT: New pending orders added by other sessions
    -- will appear in subsequent FETCHes
    FETCH NEXT FROM pending_orders INTO @order_id, @customer_id, @total;
END
 
PRINT 'Processed ' + CAST(@processed_count AS VARCHAR) + ' orders';
 
CLOSE pending_orders;
DEALLOCATE pending_orders;
 
-- Example: Real-time inventory check
DECLARE @product_id INT, @stock INT, @reserved INT;
 
DECLARE live_inventory CURSOR DYNAMIC FOR
    SELECT product_id, stock_level, reserved_quantity
    FROM inventory
    WHERE stock_level - reserved_quantity < reorder_level
    FOR UPDATE OF stock_level;
 
OPEN live_inventory;
 
FETCH NEXT FROM live_inventory INTO @product_id, @stock, @reserved;
 
WHILE @@FETCH_STATUS = 0
BEGIN
    -- Current values reflect real-time state
    PRINT 'Product ' + CAST(@product_id AS VARCHAR) + 
          ' needs reorder: ' + CAST(@stock - @reserved AS VARCHAR) + ' available';
    
    -- Positioned update with current data
    UPDATE inventory
    SET stock_level = stock_level + 100,
        last_reorder_date = GETDATE()
    WHERE CURRENT OF live_inventory;
    
    FETCH NEXT FROM live_inventory INTO @product_id, @stock, @reserved;
END
 
CLOSE live_inventory;
DEALLOCATE live_inventory;

Handle the Unexpected

With dynamic cursors, your iteration count is unpredictable. Always include safeguards: maximum iteration limits, timeout checks, or detection of unexpected growth. A dynamic cursor on a table with high insert rate could iterate indefinitely.

When to Use Dynamic

•Real-time monitoring dashboards
•Queue processing (see new items)
•Positioned UPDATE/DELETE required
•Very large result sets (no copy)
•Must reflect other sessions' changes

When to Avoid Dynamic

•Reports requiring consistent totals
•When phantom rows cause logic errors
•Complex queries with high per-fetch cost
•Need for backward scrolling
•Predictable iteration count required

Keyset-Driven Cursors

A keyset cursor is a hybrid between static and dynamic. At OPEN time, it captures the unique keys (primary key or unique identifier) of all matching rows—but not the data values. When you FETCH, it uses the stored keys to retrieve current column values from the base tables.

Declaration:

-- SQL Server
DECLARE my_cursor CURSOR KEYSET FOR
    SELECT * FROM orders WHERE status = 'pending';

Note: Keyset cursors are primarily a SQL Server concept. Other databases achieve similar behavior through different mechanisms.

Converting Mermaid diagram...

Keyset Cursor Characteristics:

Keyset Cursor Behavior
Aspect	Behavior	Notes
Membership	Fixed at OPEN	Keys captured once; new matching rows not visible
Values	Current at FETCH	Column values fetched fresh from base tables
INSERT by others	Not visible	Row key not in keyset
UPDATE by others	Visible	Same key, fetch returns new values
DELETE by others	Detected	FETCH returns @@FETCH_STATUS = -2
Memory	Moderate	Keys only, not full row copies
Scrollability	Full	Supports all FETCH directions
Positioned updates	Supported	WHERE CURRENT OF works

keyset_cursor_example.sql
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-- Keyset cursor example
-- Scenario: Review and adjust prices for specific products
 
DECLARE @product_id INT, @name VARCHAR(100), @price DECIMAL(10,2);
DECLARE @original_price DECIMAL(10,2);
 
DECLARE price_review CURSOR KEYSET FOR
    SELECT product_id, product_name, unit_price
    FROM products
    WHERE category_id = 5  -- Electronics
    ORDER BY product_name
    FOR UPDATE OF unit_price;
 
OPEN price_review;
 
FETCH NEXT FROM price_review INTO @product_id, @name, @price;
 
WHILE @@FETCH_STATUS = 0
BEGIN
    SET @original_price = @price;
    
    -- If another user updated the price, we see it now
    -- (keyset fetches current values)
    SELECT @price = unit_price FROM products WHERE product_id = @product_id;
    
    -- Detect concurrent price changes
    IF @price <> @original_price
        PRINT 'Note: Price was concurrently modified for ' + @name;
    
    -- Apply adjustment through the cursor
    IF @price < 50
    BEGIN
        UPDATE products
        SET unit_price = unit_price * 1.10  -- 10% increase for low-priced items
        WHERE CURRENT OF price_review;
    END
    
    FETCH NEXT FROM price_review INTO @product_id, @name, @price;
    
    -- Handle deleted rows (check @@FETCH_STATUS)
    IF @@FETCH_STATUS = -2
    BEGIN
        PRINT 'Row was deleted by another user, skipping...';
        FETCH NEXT FROM price_review INTO @product_id, @name, @price;
    END
END
 
CLOSE price_review;
DEALLOCATE price_review;
 
-- Understanding @@FETCH_STATUS with keyset cursors:
-- 0  = Successfully fetched a row
-- -1 = Past end of cursor or error
-- -2 = Row is missing (was deleted and key no longer exists)
 
DECLARE keyset_demo CURSOR KEYSET FOR
    SELECT order_id, status FROM orders;
 
OPEN keyset_demo;
 
FETCH NEXT FROM keyset_demo INTO @order_id, @status;
 
WHILE @@FETCH_STATUS <> -1  -- While not at end
BEGIN
    IF @@FETCH_STATUS = 0
    BEGIN
        -- Normal row - process it
        PRINT 'Processing Order: ' + CAST(@order_id AS VARCHAR);
    END
    ELSE IF @@FETCH_STATUS = -2
    BEGIN
        -- Row was deleted - log it
        PRINT 'Order was deleted, cannot process';
    END
    
    FETCH NEXT FROM keyset_demo INTO @order_id, @status;
END
 
CLOSE keyset_demo;
DEALLOCATE keyset_demo;

Best of Both Worlds

Keyset cursors offer an excellent balance: predictable row count (like static), current values (like dynamic), and full scrollability. They're ideal when you need to iterate a fixed set of records but want to see value updates made by concurrent transactions.

Keyset Cursor Requirements:

Keyset cursors require a unique key to be identifiable for each row. This means:

The underlying table must have a primary key or unique index
The cursor's SELECT must include columns that identify each row uniquely
If the query involves joins, keyset behavior may be limited

If these requirements aren't met, SQL Server may silently convert your KEYSET cursor to a STATIC cursor.

Fast Forward-Only Cursors

Fast forward-only cursors are the most optimized cursor type for sequential, read-only processing. They combine forward-only navigation with read-only access to enable maximum performance optimizations.

Declaration:

-- SQL Server: FAST_FORWARD (combined optimization)
DECLARE my_cursor CURSOR FAST_FORWARD FOR
    SELECT * FROM orders WHERE status = 'pending';

-- Equivalent:
DECLARE my_cursor CURSOR FORWARD_ONLY READ_ONLY FOR
    SELECT * FROM orders WHERE status = 'pending';

Fast Forward-Only Optimizations
Optimization	Description	Benefit
No Materialization	Results streamed directly	Minimal memory
No Backward State	No need to track previous rows	Faster FETCH
No Lock Overhead	Read-only, no update locks	Better concurrency
Minimal Context	Simpler cursor state management	Lower overhead
Streaming Possible	Can start returning rows immediately	Faster first row
No Key Storage	Unlike keyset, no key set maintained	Memory efficient

fast_forward_example.sql
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-- Fast forward-only: Optimal for simple iteration
-- This is the MOST EFFICIENT cursor type for read-only sequential processing
 
DECLARE @customer_id INT, @name VARCHAR(100), @email VARCHAR(200);
DECLARE @count INT = 0;
 
DECLARE customer_cursor CURSOR FAST_FORWARD FOR
    SELECT customer_id, customer_name, email
    FROM customers
    WHERE active = 1
    ORDER BY customer_name;
 
OPEN customer_cursor;
 
FETCH NEXT FROM customer_cursor INTO @customer_id, @name, @email;
 
WHILE @@FETCH_STATUS = 0
BEGIN
    -- Simple processing
    IF @email IS NOT NULL
        EXEC dbo.SendNewsletter @customer_id, @email;
    
    SET @count = @count + 1;
    
    FETCH NEXT FROM customer_cursor INTO @customer_id, @name, @email;
END
 
PRINT 'Processed ' + CAST(@count AS VARCHAR) + ' customers';
 
CLOSE customer_cursor;
DEALLOCATE customer_cursor;
 
-- Performance comparison demonstration
-- Setup: 100,000 row table
 
-- FAST_FORWARD: ~2 seconds
DECLARE fast_cursor CURSOR FAST_FORWARD FOR
    SELECT id, data FROM large_table;
 
-- DYNAMIC: ~5 seconds (per-fetch overhead)
DECLARE dynamic_cursor CURSOR DYNAMIC FOR
    SELECT id, data FROM large_table;
 
-- STATIC: ~10 seconds (long OPEN, then fast FETCHes)
DECLARE static_cursor CURSOR STATIC FOR
    SELECT id, data FROM large_table;
 
-- But remember: SET-BASED is still ~0.1 seconds!
SELECT id, data FROM large_table;

FORWARD_ONLY vs FAST_FORWARD:

SQL Server distinction:

FORWARD_ONLY: Restricts navigation to FETCH NEXT only, but allows other options (READ_ONLY, FOR UPDATE, different types)
FAST_FORWARD: A specific optimization that combines FORWARD_ONLY + READ_ONLY, enabling all possible optimizations

-- These are NOT equivalent:
DECLARE cur1 CURSOR FORWARD_ONLY FOR SELECT * FROM t;  -- May be dynamic or static
DECLARE cur2 CURSOR FAST_FORWARD FOR SELECT * FROM t;  -- Maximum optimization

Default to FAST_FORWARD

When you need a cursor and don't require scrolling or updates, always use FAST_FORWARD. It should be your default cursor type. Only add capabilities (SCROLL, FOR UPDATE) when specifically required.

When to Use FAST_FORWARD

•Simple sequential iteration
•Read-only reporting/export
•ETL row-by-row processing
•Sending notifications/emails
•Any one-pass, no-update scenario

When FAST_FORWARD Isn't Enough

•Need to scroll backward (use STATIC or KEYSET)
•Need positioned UPDATE/DELETE (use KEYSET or DYNAMIC)
•Need random position access (use SCROLL cursors)
•Must guarantee snapshot consistency (use STATIC)

Cursor Type Selection Guide

Choosing the right cursor type requires understanding your requirements across multiple dimensions. Use this decision framework:

Converting Mermaid diagram...

Cursor Type Selection Matrix
Requirement	Best Choice	Alternative	Avoid
Simple sequential iteration	FAST_FORWARD	FORWARD_ONLY	SCROLL cursors
Positioned UPDATE/DELETE	KEYSET or DYNAMIC		STATIC, FAST_FORWARD
Bidirectional navigation	KEYSET or STATIC	SCROLL + type	FORWARD_ONLY
Report with consistent totals	STATIC		DYNAMIC
Real-time monitoring	DYNAMIC		STATIC (stale)
Large result set, read-only	FAST_FORWARD	DYNAMIC	STATIC (memory)
See updates, ignore inserts	KEYSET		DYNAMIC, STATIC
Minimum resource usage	FAST_FORWARD	DYNAMIC	STATIC

cursor_type_recommendations.sql
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-- RECOMMENDED: Start with FAST_FORWARD, add complexity only when needed
 
-- Scenario 1: Export data to file (read-only, sequential)
-- BEST: FAST_FORWARD
DECLARE export_cursor CURSOR FAST_FORWARD FOR
    SELECT * FROM transactions WHERE export_date IS NULL;
 
-- Scenario 2: Apply discounts to specific orders
-- BEST: KEYSET (update capability, stable membership)
DECLARE discount_cursor CURSOR KEYSET FOR
    SELECT order_id, total FROM orders WHERE eligible_for_discount = 1
    FOR UPDATE OF total;
 
-- Scenario 3: Generate financial report (consistency critical)
-- BEST: STATIC (snapshot isolation)
DECLARE report_cursor CURSOR STATIC FOR
    SELECT account_id, balance FROM accounts WHERE account_type = 'savings';
 
-- Scenario 4: Monitor and process queue items (see new items)
-- BEST: DYNAMIC (real-time visibility)
DECLARE queue_cursor CURSOR DYNAMIC FOR
    SELECT queue_id, payload FROM job_queue WHERE processed = 0
    FOR UPDATE;
 
-- Scenario 5: Navigate product catalog (jump to positions)
-- BEST: KEYSET SCROLL (scrollable, updatable)
DECLARE catalog_cursor CURSOR KEYSET SCROLL FOR
    SELECT product_id, name, price FROM products WHERE active = 1
    ORDER BY category, name;

Always Ask: Do I Need a Cursor?

Before choosing a cursor type, always ask whether you need a cursor at all. Set-based operations outperform even the fastest cursor type. Use cursors only when row-by-row logic is genuinely required.

Performance Characteristics Comparison

Understanding the performance profile of each cursor type helps you make informed decisions. Here's a detailed breakdown:

Cursor Type Performance Profile
Metric	FAST_FORWARD	DYNAMIC	KEYSET	STATIC
OPEN Time	Fast (no materialization)	Fast (no materialization)	Moderate (key extraction)	Slow (full copy)
FETCH Time	Fastest	Slower (table access)	Moderate (lookup by key)	Fastest (from copy)
Memory Usage	Minimal	Minimal	Keys only (moderate)	Full result set (high)
Temp Space	None	None	Key storage	Full result set
First Row Latency	Best	Good	Moderate	Worst (copy first)
Concurrency Impact	Minimal	Higher (per-fetch locks)	Moderate	Minimal (snapshot)
Scalability (large results)	Excellent	Good	Moderate	Poor (memory bound)

Benchmark Example:

Processing 100,000 rows from a medium-complexity query:

Cursor Type	OPEN	100K FETCHes	CLOSE	Total
FAST_FORWARD	0.1s	8s	0.01s	~8s
DYNAMIC	0.1s	15s	0.01s	~15s
KEYSET	2s	10s	0.1s	~12s
STATIC	5s	6s	0.1s	~11s
SET-BASED				~0.5s

Note: These are illustrative figures; actual performance varies significantly based on hardware, query complexity, and data characteristics.

The SET-BASED Elephant

Notice that set-based processing is an order of magnitude faster than even the best cursor. The 16x-30x performance gap illustrates why cursors should be a last resort, not a first approach.

Resource Consumption Patterns:

STATIC:

Spike at OPEN (memory allocation, data copy)
Steady during fetches (reading from temp)
May cause tempdb growth issues

DYNAMIC:

Minimal at OPEN
Each FETCH hits base tables (I/O per fetch)
May cause lock escalation over time

KEYSET:

Moderate at OPEN (key extraction)
Each FETCH does key lookup
Balanced resource profile

FAST_FORWARD:

Minimal throughout
Best resource efficiency
Ideal for simple iteration

Summary: Cursor Types

Understanding cursor types enables you to make informed decisions balancing functionality, performance, and resource consumption. Let's consolidate the key concepts:

Key Takeaways

•STATIC (Insensitive): Complete snapshot at OPEN; consistent but memory-heavy; ideal for reports requiring self-consistency.
•DYNAMIC (Sensitive): Real-time view of data; sees all changes including phantoms; ideal for monitoring and queue processing.
•KEYSET: Hybrid—fixed membership, current values; best balance for updatable cursors with scrolling needs.
•FAST_FORWARD: Maximum optimization for read-only sequential access; should be your default cursor type.
•Choose based on requirements: Sensitivity, scrollability, updatability, and resource constraints drive the decision.
•Always consider set-based first: No cursor type approaches set-based performance; use cursors only when necessary.
•Explicitly specify type: Don't rely on defaults (ASENSITIVE); always declare the cursor type you need.

What's Next:

With comprehensive knowledge of cursor types, the final page addresses the most important question: when should you actually use cursors? We'll examine legitimate use cases, alternatives to cursors, and best practices for cursor-based development in production systems.

Page Complete

You now understand all major cursor types: their internal mechanics, behavior characteristics, performance profiles, and selection criteria. You can choose the appropriate cursor type for any scenario balancing functionality against resource consumption. Next, we'll examine when to use cursors—and when to choose better alternatives.

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Database Management SystemsCursors

Cursors in SQL

LevelAdvanced

Duration90 mins

TopicCursors

4 / 5

Cursor Types

Choosing the Right Cursor for the Job

Not all cursors are created equal. The type of cursor you choose fundamentally affects:

What you see: Does the cursor show a frozen snapshot or live data?
How you navigate: Can you scroll backward or only forward?
Resource consumption: How much memory and I/O does it require?
Concurrency behavior: How does it interact with other transactions?
Update capability: Can you modify data through the cursor?

What You Will Learn

Cursor Type Classification

Cursor types are classified along two primary dimensions:

1. Sensitivity: Does the cursor see changes made to underlying data after it opens?

Insensitive (Static): Sees snapshot at OPEN time only
Sensitive (Dynamic): Sees all changes in real-time
Keyset: Hybrid—membership frozen, values current

2. Scrollability: What navigation directions are supported?

Forward-only: FETCH NEXT only
Scrollable: FETCH in any direction (NEXT, PRIOR, FIRST, LAST, ABSOLUTE, RELATIVE)

These dimensions combine to create practical cursor types:

Cursor Type Matrix
Type	Sensitivity	Scrollability	Memory	Sees INSERTs	Sees UPDATEs	Sees DELETEs
STATIC	Insensitive	Scrollable	High	No	No	No
KEYSET	Partial	Scrollable	Moderate	No	Yes	Detected
DYNAMIC	Sensitive	Scrollable*	Low	Yes	Yes	Yes
FAST_FORWARD	Asensitive	Forward-only	Minimal	Varies	Varies	Varies
FORWARD_ONLY	Typically Dynamic	Forward-only	Low	Yes	Yes	Yes

Converting Mermaid diagram...

SQL Server Terminology vs. Standard SQL:

SQL Server	Standard SQL	Description
STATIC	INSENSITIVE	Snapshot isolation
DYNAMIC	SENSITIVE	Real-time view
KEYSET	(no equivalent)	Key-driven hybrid
FAST_FORWARD	(optimization)	Optimized forward-only read-only

Default Behavior Varies

Static (Insensitive) Cursors

Declaration:

-- SQL Server
DECLARE my_cursor CURSOR STATIC FOR
    SELECT * FROM orders WHERE status = 'pending';

-- Standard SQL
DECLARE my_cursor INSENSITIVE CURSOR FOR
    SELECT * FROM orders WHERE status = 'pending';

Converting Mermaid diagram...

Static Cursor Characteristics:

Static Cursor Behavior

•Complete Isolation: No visibility to concurrent INSERTs, UPDATEs, or DELETEs
•Scrollable: Supports all FETCH directions (NEXT, PRIOR, FIRST, LAST, ABSOLUTE, RELATIVE)
•Consistent Iteration: Row count and values remain constant throughout cursor lifetime
•Memory Intensive: Entire result set copied to temporary storage
•No Positioned Updates: Cannot use WHERE CURRENT OF (working on copy, not original)
•OPEN is expensive: Time to copy scales with result set size

static_cursor_example.sql
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-- Static cursor for consistent reporting
DECLARE @product_id INT, @product_name VARCHAR(100), @stock INT;
DECLARE @total_products INT = 0;
DECLARE @low_stock_count INT = 0;
 
DECLARE inventory_report CURSOR STATIC FOR
    SELECT product_id, product_name, stock_level
    FROM inventory
    WHERE warehouse_id = 1
    ORDER BY product_name;
 
OPEN inventory_report;
 
-- Even if another user modifies inventory during this loop,
-- we see a consistent snapshot
FETCH NEXT FROM inventory_report INTO @product_id, @product_name, @stock;
 
WHILE @@FETCH_STATUS = 0
BEGIN
    SET @total_products = @total_products + 1;
    
    IF @stock < 10
        SET @low_stock_count = @low_stock_count + 1;
    
    -- All logic based on consistent data
    PRINT @product_name + ': ' + CAST(@stock AS VARCHAR) + ' units';
    
    FETCH NEXT FROM inventory_report INTO @product_id, @product_name, @stock;
END
 
-- Report totals are consistent with detail rows
PRINT 'Total Products: ' + CAST(@total_products AS VARCHAR);
PRINT 'Low Stock Items: ' + CAST(@low_stock_count AS VARCHAR);
 
CLOSE inventory_report;
DEALLOCATE inventory_report;
 
-- Demonstration of scrollability
DECLARE scroll_demo CURSOR STATIC SCROLL FOR
    SELECT employee_id, hire_date
    FROM employees
    ORDER BY hire_date;
 
OPEN scroll_demo;
 
-- Jump to 10th employee
FETCH ABSOLUTE 10 FROM scroll_demo INTO @emp_id, @date;
PRINT '10th hired: Employee ' + CAST(@emp_id AS VARCHAR);
 
-- Jump to last employee
FETCH LAST FROM scroll_demo INTO @emp_id, @date;
PRINT 'Most recent: Employee ' + CAST(@emp_id AS VARCHAR);
 
-- Go back 5 positions
FETCH RELATIVE -5 FROM scroll_demo INTO @emp_id, @date;
PRINT '5 from end: Employee ' + CAST(@emp_id AS VARCHAR);
 
CLOSE scroll_demo;
DEALLOCATE scroll_demo;

When to Use Static

•Report generation requiring consistency
•Result sets that fit comfortably in memory
•Need for bidirectional navigation
•Calculations that must not be affected by concurrent changes
•Data export/archival processes

When to Avoid Static

•Very large result sets (memory pressure)
•Need to see real-time data changes
•Positioned UPDATE/DELETE required
•Long-running processes on busy tables
•When copy overhead exceeds benefit

Memory Consumption Alert

Dynamic (Sensitive) Cursors

Declaration:

-- SQL Server
DECLARE my_cursor CURSOR DYNAMIC FOR
    SELECT * FROM orders WHERE status = 'pending';

-- Standard SQL
DECLARE my_cursor SENSITIVE CURSOR FOR
    SELECT * FROM orders WHERE status = 'pending';

Converting Mermaid diagram...

Dynamic Cursor Characteristics:

Dynamic Cursor Behavior

•Full Sensitivity: Sees all INSERTs, UPDATEs, and DELETEs in real-time
•Phantom Rows: New rows matching criteria can appear during iteration
•Disappearing Rows: Rows can vanish if deleted or modified to not match criteria
•Low Memory: No result set copy—points directly to tables
•Higher I/O: Each FETCH may require table access
•Positioned Updates Supported: Can use WHERE CURRENT OF
•Limited Scrollability: Some platforms restrict PRIOR/ABSOLUTE operations

dynamic_cursor_example.sql
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-- Dynamic cursor for real-time monitoring
-- Scenario: Process pending orders, seeing new ones as they arrive
 
DECLARE @order_id INT, @customer_id INT, @total DECIMAL(10,2);
DECLARE @processed_count INT = 0;
DECLARE @max_to_process INT = 1000;  -- Safety limit
 
DECLARE pending_orders CURSOR DYNAMIC FOR
    SELECT order_id, customer_id, total_amount
    FROM orders
    WHERE status = 'pending'
    ORDER BY order_date;
 
OPEN pending_orders;
 
FETCH NEXT FROM pending_orders INTO @order_id, @customer_id, @total;
 
WHILE @@FETCH_STATUS = 0 AND @processed_count < @max_to_process
BEGIN
    -- Process this order
    BEGIN TRY
        EXEC dbo.ProcessSingleOrder @order_id;
        
        -- Mark as processed (this UPDATE is visible to cursor!)
        UPDATE orders SET status = 'processed' WHERE order_id = @order_id;
        
        SET @processed_count = @processed_count + 1;
    END TRY
    BEGIN CATCH
        -- Handle error, order remains pending
        PRINT 'Failed to process order ' + CAST(@order_id AS VARCHAR);
    END CATCH
    
    -- IMPORTANT: New pending orders added by other sessions
    -- will appear in subsequent FETCHes
    FETCH NEXT FROM pending_orders INTO @order_id, @customer_id, @total;
END
 
PRINT 'Processed ' + CAST(@processed_count AS VARCHAR) + ' orders';
 
CLOSE pending_orders;
DEALLOCATE pending_orders;
 
-- Example: Real-time inventory check
DECLARE @product_id INT, @stock INT, @reserved INT;
 
DECLARE live_inventory CURSOR DYNAMIC FOR
    SELECT product_id, stock_level, reserved_quantity
    FROM inventory
    WHERE stock_level - reserved_quantity < reorder_level
    FOR UPDATE OF stock_level;
 
OPEN live_inventory;
 
FETCH NEXT FROM live_inventory INTO @product_id, @stock, @reserved;
 
WHILE @@FETCH_STATUS = 0
BEGIN
    -- Current values reflect real-time state
    PRINT 'Product ' + CAST(@product_id AS VARCHAR) + 
          ' needs reorder: ' + CAST(@stock - @reserved AS VARCHAR) + ' available';
    
    -- Positioned update with current data
    UPDATE inventory
    SET stock_level = stock_level + 100,
        last_reorder_date = GETDATE()
    WHERE CURRENT OF live_inventory;
    
    FETCH NEXT FROM live_inventory INTO @product_id, @stock, @reserved;
END
 
CLOSE live_inventory;
DEALLOCATE live_inventory;

Handle the Unexpected

When to Use Dynamic

•Real-time monitoring dashboards
•Queue processing (see new items)
•Positioned UPDATE/DELETE required
•Very large result sets (no copy)
•Must reflect other sessions' changes

When to Avoid Dynamic

•Reports requiring consistent totals
•When phantom rows cause logic errors
•Complex queries with high per-fetch cost
•Need for backward scrolling
•Predictable iteration count required

Keyset-Driven Cursors

Declaration:

-- SQL Server
DECLARE my_cursor CURSOR KEYSET FOR
    SELECT * FROM orders WHERE status = 'pending';

Note: Keyset cursors are primarily a SQL Server concept. Other databases achieve similar behavior through different mechanisms.

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Keyset Cursor Characteristics:

Keyset Cursor Behavior
Aspect	Behavior	Notes
Membership	Fixed at OPEN	Keys captured once; new matching rows not visible
Values	Current at FETCH	Column values fetched fresh from base tables
INSERT by others	Not visible	Row key not in keyset
UPDATE by others	Visible	Same key, fetch returns new values
DELETE by others	Detected	FETCH returns @@FETCH_STATUS = -2
Memory	Moderate	Keys only, not full row copies
Scrollability	Full	Supports all FETCH directions
Positioned updates	Supported	WHERE CURRENT OF works

keyset_cursor_example.sql
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-- Keyset cursor example
-- Scenario: Review and adjust prices for specific products
 
DECLARE @product_id INT, @name VARCHAR(100), @price DECIMAL(10,2);
DECLARE @original_price DECIMAL(10,2);
 
DECLARE price_review CURSOR KEYSET FOR
    SELECT product_id, product_name, unit_price
    FROM products
    WHERE category_id = 5  -- Electronics
    ORDER BY product_name
    FOR UPDATE OF unit_price;
 
OPEN price_review;
 
FETCH NEXT FROM price_review INTO @product_id, @name, @price;
 
WHILE @@FETCH_STATUS = 0
BEGIN
    SET @original_price = @price;
    
    -- If another user updated the price, we see it now
    -- (keyset fetches current values)
    SELECT @price = unit_price FROM products WHERE product_id = @product_id;
    
    -- Detect concurrent price changes
    IF @price <> @original_price
        PRINT 'Note: Price was concurrently modified for ' + @name;
    
    -- Apply adjustment through the cursor
    IF @price < 50
    BEGIN
        UPDATE products
        SET unit_price = unit_price * 1.10  -- 10% increase for low-priced items
        WHERE CURRENT OF price_review;
    END
    
    FETCH NEXT FROM price_review INTO @product_id, @name, @price;
    
    -- Handle deleted rows (check @@FETCH_STATUS)
    IF @@FETCH_STATUS = -2
    BEGIN
        PRINT 'Row was deleted by another user, skipping...';
        FETCH NEXT FROM price_review INTO @product_id, @name, @price;
    END
END
 
CLOSE price_review;
DEALLOCATE price_review;
 
-- Understanding @@FETCH_STATUS with keyset cursors:
-- 0  = Successfully fetched a row
-- -1 = Past end of cursor or error
-- -2 = Row is missing (was deleted and key no longer exists)
 
DECLARE keyset_demo CURSOR KEYSET FOR
    SELECT order_id, status FROM orders;
 
OPEN keyset_demo;
 
FETCH NEXT FROM keyset_demo INTO @order_id, @status;
 
WHILE @@FETCH_STATUS <> -1  -- While not at end
BEGIN
    IF @@FETCH_STATUS = 0
    BEGIN
        -- Normal row - process it
        PRINT 'Processing Order: ' + CAST(@order_id AS VARCHAR);
    END
    ELSE IF @@FETCH_STATUS = -2
    BEGIN
        -- Row was deleted - log it
        PRINT 'Order was deleted, cannot process';
    END
    
    FETCH NEXT FROM keyset_demo INTO @order_id, @status;
END
 
CLOSE keyset_demo;
DEALLOCATE keyset_demo;

Best of Both Worlds

Keyset Cursor Requirements:

Keyset cursors require a unique key to be identifiable for each row. This means:

The underlying table must have a primary key or unique index
The cursor's SELECT must include columns that identify each row uniquely
If the query involves joins, keyset behavior may be limited

If these requirements aren't met, SQL Server may silently convert your KEYSET cursor to a STATIC cursor.

Fast Forward-Only Cursors

Declaration:

-- SQL Server: FAST_FORWARD (combined optimization)
DECLARE my_cursor CURSOR FAST_FORWARD FOR
    SELECT * FROM orders WHERE status = 'pending';

-- Equivalent:
DECLARE my_cursor CURSOR FORWARD_ONLY READ_ONLY FOR
    SELECT * FROM orders WHERE status = 'pending';

Fast Forward-Only Optimizations
Optimization	Description	Benefit
No Materialization	Results streamed directly	Minimal memory
No Backward State	No need to track previous rows	Faster FETCH
No Lock Overhead	Read-only, no update locks	Better concurrency
Minimal Context	Simpler cursor state management	Lower overhead
Streaming Possible	Can start returning rows immediately	Faster first row
No Key Storage	Unlike keyset, no key set maintained	Memory efficient

fast_forward_example.sql
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-- Fast forward-only: Optimal for simple iteration
-- This is the MOST EFFICIENT cursor type for read-only sequential processing
 
DECLARE @customer_id INT, @name VARCHAR(100), @email VARCHAR(200);
DECLARE @count INT = 0;
 
DECLARE customer_cursor CURSOR FAST_FORWARD FOR
    SELECT customer_id, customer_name, email
    FROM customers
    WHERE active = 1
    ORDER BY customer_name;
 
OPEN customer_cursor;
 
FETCH NEXT FROM customer_cursor INTO @customer_id, @name, @email;
 
WHILE @@FETCH_STATUS = 0
BEGIN
    -- Simple processing
    IF @email IS NOT NULL
        EXEC dbo.SendNewsletter @customer_id, @email;
    
    SET @count = @count + 1;
    
    FETCH NEXT FROM customer_cursor INTO @customer_id, @name, @email;
END
 
PRINT 'Processed ' + CAST(@count AS VARCHAR) + ' customers';
 
CLOSE customer_cursor;
DEALLOCATE customer_cursor;
 
-- Performance comparison demonstration
-- Setup: 100,000 row table
 
-- FAST_FORWARD: ~2 seconds
DECLARE fast_cursor CURSOR FAST_FORWARD FOR
    SELECT id, data FROM large_table;
 
-- DYNAMIC: ~5 seconds (per-fetch overhead)
DECLARE dynamic_cursor CURSOR DYNAMIC FOR
    SELECT id, data FROM large_table;
 
-- STATIC: ~10 seconds (long OPEN, then fast FETCHes)
DECLARE static_cursor CURSOR STATIC FOR
    SELECT id, data FROM large_table;
 
-- But remember: SET-BASED is still ~0.1 seconds!
SELECT id, data FROM large_table;

FORWARD_ONLY vs FAST_FORWARD:

SQL Server distinction:

FORWARD_ONLY: Restricts navigation to FETCH NEXT only, but allows other options (READ_ONLY, FOR UPDATE, different types)
FAST_FORWARD: A specific optimization that combines FORWARD_ONLY + READ_ONLY, enabling all possible optimizations

-- These are NOT equivalent:
DECLARE cur1 CURSOR FORWARD_ONLY FOR SELECT * FROM t;  -- May be dynamic or static
DECLARE cur2 CURSOR FAST_FORWARD FOR SELECT * FROM t;  -- Maximum optimization

Default to FAST_FORWARD

When you need a cursor and don't require scrolling or updates, always use FAST_FORWARD. It should be your default cursor type. Only add capabilities (SCROLL, FOR UPDATE) when specifically required.

When to Use FAST_FORWARD

•Simple sequential iteration
•Read-only reporting/export
•ETL row-by-row processing
•Sending notifications/emails
•Any one-pass, no-update scenario

When FAST_FORWARD Isn't Enough

•Need to scroll backward (use STATIC or KEYSET)
•Need positioned UPDATE/DELETE (use KEYSET or DYNAMIC)
•Need random position access (use SCROLL cursors)
•Must guarantee snapshot consistency (use STATIC)

Cursor Type Selection Guide

Choosing the right cursor type requires understanding your requirements across multiple dimensions. Use this decision framework:

Converting Mermaid diagram...

Cursor Type Selection Matrix
Requirement	Best Choice	Alternative	Avoid
Simple sequential iteration	FAST_FORWARD	FORWARD_ONLY	SCROLL cursors
Positioned UPDATE/DELETE	KEYSET or DYNAMIC		STATIC, FAST_FORWARD
Bidirectional navigation	KEYSET or STATIC	SCROLL + type	FORWARD_ONLY
Report with consistent totals	STATIC		DYNAMIC
Real-time monitoring	DYNAMIC		STATIC (stale)
Large result set, read-only	FAST_FORWARD	DYNAMIC	STATIC (memory)
See updates, ignore inserts	KEYSET		DYNAMIC, STATIC
Minimum resource usage	FAST_FORWARD	DYNAMIC	STATIC

cursor_type_recommendations.sql
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-- RECOMMENDED: Start with FAST_FORWARD, add complexity only when needed
 
-- Scenario 1: Export data to file (read-only, sequential)
-- BEST: FAST_FORWARD
DECLARE export_cursor CURSOR FAST_FORWARD FOR
    SELECT * FROM transactions WHERE export_date IS NULL;
 
-- Scenario 2: Apply discounts to specific orders
-- BEST: KEYSET (update capability, stable membership)
DECLARE discount_cursor CURSOR KEYSET FOR
    SELECT order_id, total FROM orders WHERE eligible_for_discount = 1
    FOR UPDATE OF total;
 
-- Scenario 3: Generate financial report (consistency critical)
-- BEST: STATIC (snapshot isolation)
DECLARE report_cursor CURSOR STATIC FOR
    SELECT account_id, balance FROM accounts WHERE account_type = 'savings';
 
-- Scenario 4: Monitor and process queue items (see new items)
-- BEST: DYNAMIC (real-time visibility)
DECLARE queue_cursor CURSOR DYNAMIC FOR
    SELECT queue_id, payload FROM job_queue WHERE processed = 0
    FOR UPDATE;
 
-- Scenario 5: Navigate product catalog (jump to positions)
-- BEST: KEYSET SCROLL (scrollable, updatable)
DECLARE catalog_cursor CURSOR KEYSET SCROLL FOR
    SELECT product_id, name, price FROM products WHERE active = 1
    ORDER BY category, name;

Always Ask: Do I Need a Cursor?

Before choosing a cursor type, always ask whether you need a cursor at all. Set-based operations outperform even the fastest cursor type. Use cursors only when row-by-row logic is genuinely required.

Performance Characteristics Comparison

Understanding the performance profile of each cursor type helps you make informed decisions. Here's a detailed breakdown:

Cursor Type Performance Profile
Metric	FAST_FORWARD	DYNAMIC	KEYSET	STATIC
OPEN Time	Fast (no materialization)	Fast (no materialization)	Moderate (key extraction)	Slow (full copy)
FETCH Time	Fastest	Slower (table access)	Moderate (lookup by key)	Fastest (from copy)
Memory Usage	Minimal	Minimal	Keys only (moderate)	Full result set (high)
Temp Space	None	None	Key storage	Full result set
First Row Latency	Best	Good	Moderate	Worst (copy first)
Concurrency Impact	Minimal	Higher (per-fetch locks)	Moderate	Minimal (snapshot)
Scalability (large results)	Excellent	Good	Moderate	Poor (memory bound)

Benchmark Example:

Processing 100,000 rows from a medium-complexity query:

Cursor Type	OPEN	100K FETCHes	CLOSE	Total
FAST_FORWARD	0.1s	8s	0.01s	~8s
DYNAMIC	0.1s	15s	0.01s	~15s
KEYSET	2s	10s	0.1s	~12s
STATIC	5s	6s	0.1s	~11s
SET-BASED				~0.5s

Note: These are illustrative figures; actual performance varies significantly based on hardware, query complexity, and data characteristics.

The SET-BASED Elephant

Notice that set-based processing is an order of magnitude faster than even the best cursor. The 16x-30x performance gap illustrates why cursors should be a last resort, not a first approach.

Resource Consumption Patterns:

STATIC:

Spike at OPEN (memory allocation, data copy)
Steady during fetches (reading from temp)
May cause tempdb growth issues

DYNAMIC:

Minimal at OPEN
Each FETCH hits base tables (I/O per fetch)
May cause lock escalation over time

KEYSET:

Moderate at OPEN (key extraction)
Each FETCH does key lookup
Balanced resource profile

FAST_FORWARD:

Minimal throughout
Best resource efficiency
Ideal for simple iteration

Summary: Cursor Types

Understanding cursor types enables you to make informed decisions balancing functionality, performance, and resource consumption. Let's consolidate the key concepts:

Key Takeaways

•STATIC (Insensitive): Complete snapshot at OPEN; consistent but memory-heavy; ideal for reports requiring self-consistency.
•DYNAMIC (Sensitive): Real-time view of data; sees all changes including phantoms; ideal for monitoring and queue processing.
•KEYSET: Hybrid—fixed membership, current values; best balance for updatable cursors with scrolling needs.
•FAST_FORWARD: Maximum optimization for read-only sequential access; should be your default cursor type.
•Choose based on requirements: Sensitivity, scrollability, updatability, and resource constraints drive the decision.
•Always consider set-based first: No cursor type approaches set-based performance; use cursors only when necessary.
•Explicitly specify type: Don't rely on defaults (ASENSITIVE); always declare the cursor type you need.

What's Next:

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