Metadata changes to tables or views referred to by prepared
statements are detected and cause automatic repreparation of the
statement when it is next executed. This applies to prepared
statements processed at the SQL level (using the
PREPARE statement) and those
processed using the binary client-server protocol (using the
mysql_stmt_prepare() C API
Metadata changes occur for DDL statements such as those that
create, drop, alter, rename, or truncate tables, or that analyze,
optimize, or repair tables. Repreparation also occurs after
referenced tables or views are flushed from the table definition
cache, either implicitly to make room for new entries in the
cache, or explicitly due to
Repreparation is automatic, but to the extent that it occurs, performance of prepared statements is diminished.
When a statement is reprepared, the default database and SQL mode that were in effect for the original preparation are used.
An incompatibility with previous versions of MySQL is that a
prepared statement may return a different set of columns or
different column types from one execution to the next. For
example, if the prepared statement is
SELECT * FROM
t1 to contain a
different number of columns causes the next execution to return a
number of columns different from the previous execution.
Older versions of the client library cannot handle this change in behavior. For applications that use prepared statements with a server that performs automatic repreparation, an upgrade to the new client library is strongly recommended.
Com_stmt_reprepare status variable tracks
the number of repreparations.