MySQL DATEDIFF() Function

MySQL DATEDIFF() Function: Date/Time Operations

The MySQL DATEDIFF() function calculates the number of days between two date values. It allows developers to perform deterministic data transformations directly within SQL queries.

Key Characteristics and Usage

• Category: MySQL Date/Time Function
• Return Data Type: INT
• NULL Safety: Returns NULL if any required input argument evaluates to NULL.

Function Parameters

• Parameters: expr1, expr2

Practical SQL Code Example

-- Query demonstrating MySQL DATEDIFF() usage in production queries
SELECT DATEDIFF('2026-08-14', '2026-08-01') AS day_diff;

Expected Output

Best Practices & Common Gotchas

• NULL Value Handling: Always wrap function calls in IFNULL() or COALESCE() if your input columns allow NULL values.
• Index Usage: Using scalar functions directly on indexed columns in WHERE clauses disables B-tree index lookups (causing full table scans). Use generated columns with indexes when querying heavily.
• Type Compatibility: Ensure input argument data types match expected function inputs to avoid silent implicit conversions.

Self-Check Challenge

Write a SQL query using DATEDIFF() to format or evaluate data retrieved from a database table.