如何理解存储过程中已经存在一个mysql临时表？

Question

I use mysql temporary table to share some middle data between several stored procedures. All of these procedures use a single database connection. In every SP, I need to determine a if mysql temporary table already exists or not. if it already exists, then I'll use it's values, otherwise the SP will create & fill temporary table & other SPs (on same connection of course!) will use temporary table results.

But I don't know how should I check if the temporary table already exists or not, I mean something like this:

IF temporaryTablename EXISTS THEN
   ...
ELSE
   ...
END IF;

any idea?

Answer 1

It has the IF NOT EXISTS ( 13.1.17. CREATE TABLE Syntax ) option when creating a table, you can use in this case.

Example:

DELIMITER $$

CREATE PROCEDURE `temp_sp1`()
BEGIN
    CREATE TEMPORARY TABLE IF NOT EXISTS `temp_table` (
      `col2` int(11) DEFAULT NULL,
      `col3` int(11) DEFAULT NULL
    );
    INSERT INTO `temp_table` (`col2`, `col3`) VALUES (4, 5);
    SELECT `col2`, `col3` FROM `temp_table`;
END$$

DELIMITER ;

SQL Fiddle demo

UPDATE

...
DECLARE `no_such_table` TINYINT(1) DEFAULT 0;
DECLARE CONTINUE HANDLER FOR SQLSTATE VALUE '42S02' SET `no_such_table` := 1;
DO (SELECT NULL FROM `temp_table` LIMIT 0);
IF (`no_such_table`) THEN
   ...  
ELSE
   ...  
END IF;
...

Answer 2

For some reason wchiquito's UPDATE doesn't work for me, so I modified it into this:

CREATE PROCEDURE check_table_existence (IN table_name CHAR(64))
BEGIN
    DECLARE CONTINUE HANDLER FOR SQLSTATE '42S02' SET @err = 1;
    SET @err = 0;
    SET @table_name = table_name;
    SET @sql_query = CONCAT('SELECT NULL FROM ',@table_name);
    PREPARE stmt1 FROM @sql_query;
    IF (@err = 1) THEN
        SET @table_exists = 0;
    ELSE
        SET @table_exists = 1;
        DEALLOCATE PREPARE stmt1;
    END IF;
END

Then:

CALL check_table_existence('existent_table');
SELECT @table_exists;

gives

+---------------+
| @table_exists |
+---------------+
|             1 |
+---------------+

and 0 otherwise.

It is also a workaround, but it works fine for me. It works for TEMPORARY TABLE as well.

Answer 3

I use this:

CREATE FUNCTION `TableExists`(tableName text) RETURNS bit(1)
    DETERMINISTIC
BEGIN
    return (SELECT count(*) FROM information_schema.tables where table_name = tableName and table_schema=schema() limit 1) > 0;
END