Behavior of REGEXP with NULL Values in MySQL
In MySQL, when you use the REGEXP operator on a column that contains NULL values, the result of the comparison for those rows is also NULL. MySQL treats NULL as an unknown value, so REGEXP does not match it.
NULL Evaluation: Any comparison with NULL (including REGEXP) returns NULL, which is treated as false in a WHERE clause.
No Match: Rows with NULL values in the column being tested will not appear in the result set unless explicitly handled.
Handling NULLs: To include or filter NULL values, use the
IS NULLorCOALESCEfunctions in your query.Combination Example: You can combine REGEXP with NULL checks, e.g.,
WHERE column REGEXP 'pattern' OR column IS NULL.
Understanding this behavior is important when working with columns that may contain NULLs, to avoid unintentionally missing or excluding rows in your query results.