SQL FIRST_VALUE and LAST_VALUE

Understanding FIRST_VALUE and LAST_VALUE

FIRST_VALUE and LAST_VALUE are window functions that return the first and last values in a window frame, respectively. These functions are particularly useful when you need to compare each row with the boundary values in an ordered set within each partition.

Basic Syntax

Common FIRST_VALUE/LAST_VALUE Interview Questions

How would you find each user's first and most recent video views?
What's the difference between FIRST_VALUE and MIN?
Why might LAST_VALUE return unexpected results without the proper frame clause?
How can you compare each video's views with the most viewed video in its category?

Common Usage Patterns

1. Basic Usage

Compare current values with first/last values in the partition.

2. Finding High and Low Points

Identify extreme values within groups.

3. Multiple Column Analysis

Analyze patterns using multiple columns.

Best Practices

1. Always Specify Frame Clause

LAST_VALUE especially needs proper frame specification:

Use ROWS/RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING for full partition
Default frame can lead to unexpected LAST_VALUE results
Consider performance impact of large frame sizes

2. Handle NULL Values

Consider these strategies for NULL handling:

Use IGNORE NULLS option if available in your SQL version
Filter NULL values before applying window functions
Use COALESCE for custom NULL handling

3. Consider Alternatives

Choose the right function for your needs:

MIN/MAX might be simpler for basic aggregations
LAG/LEAD for adjacent row comparisons
ROW_NUMBER for simple ordering tasks

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