There are several sources of error information in MySQL:
Each SQL statement executed results in an error code, an SQLSTATE value, and an error message, as described in Section B.2, “Types of Error Values”. These errors are returned from the server side; see Section B.3, “Server Error Codes and Messages”.
Errors can occur on the client side, usually involving problems communicating with the server; see Section B.4, “Client Error Codes and Messages”.
SQL statement warning and error information is available
SHOW WARNINGS and
SHOW ERRORS statements. The
warning_count system variable
indicates the number of errors, warnings, and notes. The
error_count system variable
indicates the number of errors. Its value excludes warnings
SHOW SLAVE STATUS statement
output includes information about replication errors occurring
on the slave side.