Home/ Questions/Q 8980681
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-15T20:08:54+00:00

I was quite surprised when MySQL allowed me to insert a NULL into a

  • 0

I was quite surprised when MySQL allowed me to insert a NULL into a field that was created with NOT NULL. I did some research and discovered how to enable strict mode. However, I am not quite sure what validation MySQL does when STRICT_ALL_TABLES is enabled.

The manual says:

Strict mode controls how MySQL handles input values that are invalid or missing. A value can be invalid for several reasons. (emphasis mine) For example, it might have the wrong data type for the column, or it might be out of range.

I understand what it considers missing and how it handles that. I am unclear what it considers invalid. I’ve done some testing and discovered the following:

  • strings that are too long are invalid
  • numbers that are out of range are invalid
  • NULLs for a non-NULL column are invalid
  • TRUE and FALSE always seem to be valid (they become 1 and 0 respectively)
  • invalid dates are invalid
  • zero dates are valid (additional modes can be enabled to change this behaviour)
  • floats in an integer field are valid (they get rounded)
  • letters in a number field are invalid

Does MySQL do any other validation checks other than what is mentioned above?

The manual says ‘wrong data type for the column’, but the only situation I see where this actually comes into play is letters in a number field. Are there other examples of data type errors?

Is there a list somewhere of exactly what checks MySQL performs?

EDIT: For the record, my application already does extensive validation. I am using strict mode as a last-chance, just-in-case check. If I forget to check something, I want it to fail fast rather than ‘silently mangle my data’.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    A good resource is to check the MySQL source, and read mysql-test/t/strict.test to see all the cases they test for after setting STRICT mode or TRADITIONAL mode (which is a superset of STRICT).

    You did excellent research and testing, but there are a few more cases, such as:

    • Trying to insert an undefined ENUM value.
    • Trying to insert a default value for a NOT NULL column with no DEFAULT defined.
    • Trying to use CAST() to convert strings to integers, etc.
    • Conversion of VARCHAR to MEDIUMTEXT or LONGTEXT if you give a length greater than 65536.
    • Truncation of COMMENT strings for tables and columns.
    • Conversion of string to YEAR type.
    • Defining a SET or ENUM column with duplicate entries.

    Also mysql-test/include/strict_autoinc.inc, because it tests for overflow when an auto-inc value grows too large.

    There are a few other test files that use STRICT mode for specific tests, but I didn’t examine them.

    • 0