SIGNAL, RESIGNAL, and GET DIAGNOSTICS are not permissible as prepared statements. For example, this statement is invalid:

PREPARE stmt1 FROM 'SIGNAL SQLSTATE "02000"';

SQLSTATE values in class '04' are not treated specially. They are handled the same as other exceptions.

Standard SQL has a diagnostics area stack, containing a diagnostics area for each nested execution context. Standard SQL syntax includes GET STACKED DIAGNOSTICS for referring to stacked areas. MySQL does not support the STACKED keyword because there is a single diagnostics area containing information from the most recent statement that wrote to it. See also Section 13.6.7.7, “The MySQL Diagnostics Area”.

In standard SQL, the first condition relates to the SQLSTATE value returned for the previous SQL statement. In MySQL, this is not guaranteed, so to get the main error, you cannot do this:

GET DIAGNOSTICS CONDITION 1 @errno = MYSQL_ERRNO;

Instead, do this:

GET DIAGNOSTICS @cno = NUMBER;
GET DIAGNOSTICS CONDITION @cno @errno = MYSQL_ERRNO;