CAST vs CONVERT SQL Functions Explained
CAST and CONVERT are SQL functions that change one data type to another. CAST is the ANSI-standard way; CONVERT is SQL Server’s own flavor with extra style options.
Developers often copy-paste snippets from different sources and see both commands in the wild, so they assume they’re interchangeable. Mixing them up can quietly change date formats or silently fail on edge values.
Key Differences
CAST sticks to basic type changes and works across most databases. CONVERT adds a third “style” parameter, letting you pick date display formats like MM/dd/yyyy or yyyy-MM-dd, but it only runs on SQL Server.
Which One Should You Choose?
Use CAST when you need portability or simple type casting. Choose CONVERT only when you must control output styles in SQL Server; otherwise, stick with CAST for safer, clearer code.
Examples and Daily Life
A quick CAST turns a VARCHAR price into MONEY before math. Meanwhile, CONVERT lets you show a stored datetime as ‘01 Jun 2025’ for user reports without touching the raw data.
Can CAST handle date formats?
It changes the type, but it won’t let you pick the style; the result stays in the server’s default format.
Does CONVERT run on MySQL or PostgreSQL?
No. CONVERT is SQL Server–specific. In other systems, CAST or similar vendor functions do the job.
Are there performance gaps between the two?
Both are fast. Differences show up only when style formatting in CONVERT adds extra work; usually it’s negligible.