2004
MariaDBERRORNotableQueryHIGH confidence
Only constants are allowed here
Production Risk
Low — statement is rejected.
What this means
A SET statement or similar construct requires a constant value, but a non-constant expression or column reference was provided.
Why it happens
- 1Using a column reference or subquery where a constant is required.
- 2Dynamic expression in a SET context that only accepts literals.
How to reproduce
trigger — this will error
trigger — this will error
SET @var = col_name; -- col_name is not a constant
expected output
ERROR 2004 (HY000): You may only use constant expressions in this context.
Fix
Use a constant literal or a user variable
Use a constant literal or a user variable
SET @var = 42;
Why this works
Only literal values and session variables are accepted in this context.
Sources
Official documentation ↗
MySQL 8.0 — 2004 ER_SET_CONSTANTS_ONLY
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