Highest Unique Signal Value

Easy

You are given a SignalReadings table with one column: reading_value (integer) The table may contain duplicate values. A value is considered unique if it appears exactly once in the full table. Task: Return the largest unique value in the dataset. If no unique value exists, return NULL. Return exactly one row with this schema: largest_unique_value Supported submission environments: SQL (SQLite 3.27.2) Pandas (Python)

Example 1

Input

SignalReadings:
| reading_value |
|---------------|
| 8             |
| 8             |
| 3             |
| 3             |
| 1             |
| 4             |
| 5             |
| 6             |

Output

[{"largest_unique_value":6}]

Explanation

Unique values are 1, 4, 5, and 6. The largest among them is 6.

Example 2

Input

SignalReadings:
| reading_value |
|---------------|
| 8             |
| 8             |
| 7             |
| 7             |
| 3             |
| 3             |
| 3             |

Output

[{"largest_unique_value":null}]

Explanation

Every value appears at least twice, so no unique value exists.

Example 3

Input

SignalReadings:
| reading_value |
|---------------|
| -10           |
| -10           |
| -2            |
| 0             |
| 0             |
| 9             |
| 9             |

Output

[{"largest_unique_value":-2}]

Explanation

The only value that appears exactly once is -2, so it is returned.

Constraints

1 <= number of rows in SignalReadings <= 10,000
-1,000,000,000 <= reading_value <= 1,000,000,000
SignalReadings has no guaranteed primary key
Duplicate rows are allowed
Return exactly one row and one column: largest_unique_value
Use SQLite 3.27.2 semantics for SQL submissions
For Pandas submissions, return a one-row DataFrame with column largest_unique_value