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According to the documentation metadata for a prepared statement should be available after preparing the statement: "mysql_stmt_field_count() can be called after you have prepared a statement by invoking mysql_stmt_prepare().".
This doesn't work with all kind pf prepared statements.
How to repeat:
static int test_metadata(MYSQL *mysql) { int rc; char *query1= "SELECT 1,2 FROM DUAL"; char *query2= "SHOW CREATE TABLE test_metadata"; MYSQL_STMT *stmt= mysql_stmt_init(mysql); rc= mysql_query(mysql, "DROP TABLE IF EXISTS test_metadata"); check_mysql_rc(rc, mysql); rc= mysql_query(mysql, "CREATE TABLE test_metadata (a int)"); check_mysql_rc(rc, mysql); rc= mysql_stmt_prepare(stmt, query1, strlen(query1)); check_stmt_rc(rc, stmt); diag("Fields in result set after prepare: %u", mysql_stmt_field_count(stmt)); rc= mysql_stmt_prepare(stmt, query2, strlen(query2)); check_stmt_rc(rc, stmt); diag("Fields in result set after prepare: %u", mysql_stmt_field_count(stmt)); rc= mysql_stmt_execute(stmt); diag("Fields in result set after execute: %u", mysql_stmt_field_count(stmt)); mysql_stmt_close(stmt); }
Output:
# Fields in result set after prepare: 2 # Fields in result set after prepare: 0 # Fields in result set after execute: 2
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Yes, 5.5 fails too.
This is a problem for a whole lot of SHOW commands. The list of affected includes:
SHOW GRANTS
SHOW CREATE DATABASE
SHOW [MASTER | SLAVE] STATUS
SHOW CREATE [PROCEDURE | FUNCTION]
SHOW [PROCEDURE | FUNCTION] CODE
....
All of these return zero fields after the stmt_prepare.
Shortly speaking these are all the SHOW statemets that aren't implemented using the Inf Schema tables.
The number of fields in them is only defined on the execution stage.
I quess the nice solution for it is to extract the metadata-creation part out of the
functions like mysqld_show_create and execute it on the 'prepare' stage. But it involves a lot of coding too.
Is 5.5 affected too?