MySQL CAST() Function

MySQL CAST() Function: Cast/Control Operations

The MySQL CAST() function converts a value of one type to a specified target data type. It allows developers to perform deterministic data transformations directly within SQL queries.

Key Characteristics and Usage

• Category: MySQL Cast/Control Function
• Return Data Type: TARGET_TYPE
• NULL Safety: Returns NULL if any required input argument evaluates to NULL.

Function Parameters

• Parameters: expression AS target_type

Practical SQL Code Example

-- Query demonstrating MySQL CAST() usage in production queries
SELECT CAST('123.45' AS DECIMAL(10,2)) AS num;

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 CAST() to format or evaluate data retrieved from a database table.