This script:

SET sql_mode=DEFAULT;

CREATE OR REPLACE TABLE t1 (a TEXT);

PREPARE stmt FROM 'INSERT INTO t1 (a) VALUES (2||3)';

EXECUTE stmt;

SET sql_mode=ORACLE;

EXECUTE stmt;

ALTER TABLE t1 ADD b INT;

EXECUTE stmt;

SELECT * FROM t1;

returns:

+------+------+

| a    | b    |

+------+------+

| 1    | NULL |

| 1    | NULL |

| 23   | NULL |

+------+------+

Notice, changing sql_mode between EXECUTE and PREPARE does not change the result, || is still treated as boolean OR in the second EXECUTE. However, as soon as I do ALTER TABLE, it forces automatic statement repreparation and the meaning of || in the third EXECUTE changes to concatenation.

This should be fixed to remember sql_mode with the prepared statement, so when the automatic repreparation happens it uses the same sql_mode which was used during PREPARE.