Syntax:
SHOW WARNINGS [LIMIT [offset,] row_count]
SHOW COUNT(*) WARNINGS

SHOW WARNINGS shows information about the conditions (errors, warnings,
and notes) that resulted from the last statement in the current session
that generated messages. It shows nothing if the last statement used a
table and generated no messages. (That is, a statement that uses a
table but generates no messages clears the message list.) Statements
that do not use tables and do not generate messages have no effect on
the message list.

Warnings are generated for DML statements such as INSERT, UPDATE, and
LOAD DATA INFILE as well as DDL statements such as CREATE TABLE and
ALTER TABLE.

The LIMIT clause has the same syntax as for the SELECT statement. See
http://dev.mysql.com/doc/refman/5.0/en/select.html.

A related statement, SHOW ERRORS, shows only the error conditions (it
excludes warnings and notes). See [HELP SHOW ERRORS].

The SHOW COUNT(*) WARNINGS statement displays the total number of
errors, warnings, and notes. You can also retrieve this number from the
warning_count system variable:

SHOW COUNT(*) WARNINGS;
SELECT @@warning_count;

URL: http://dev.mysql.com/doc/refman/5.0/en/show-warnings.html

