Where clause from values for a stored procedure

How do you build and use dynamic sql in a MySQL stored procedure?


I don't believe MySQL supports dynamic sql. You can do "prepared" statements which is similar, but different.

Here is an example:

mysql> PREPARE stmt FROM
    -> 'select count(*)
    -> from information_schema.schemata
    -> where schema_name = ? or schema_name = ?'
Query OK, 0 rows affected (0.00 sec)
Statement prepared
mysql> EXECUTE stmt
    -> USING @schema1,@schema2
| count(*) |
|        2 |
1 row in set (0.00 sec)

The prepared statements are often used to see an execution plan for a given query. Since they are executed with the execute command and the sql can be assigned to a variable you can approximate the some of the same behavior as dynamic sql.

Here is a good link about this:

Don't forget to deallocate the stmt using the last line!

Good Luck!

After 5.0.13, in stored procedures, you can use dynamic SQL:

delimiter //
CREATE PROCEDURE dynamic(IN tbl CHAR(64), IN col CHAR(64))
    SET @s = CONCAT('SELECT ',col,' FROM ',tbl );
    PREPARE stmt FROM @s;
    EXECUTE stmt;
delimiter ;

Dynamic SQL does not work in functions or triggers. See the MySQL documentation for more uses.

You can pass thru outside the dynamic statement using User-Defined Variables

Server version: 5.6.25-log MySQL Community Server (GPL)

mysql> PREPARE stmt FROM 'select "AAAA" into @a';
Query OK, 0 rows affected (0.01 sec)
Statement prepared

mysql> EXECUTE stmt;
Query OK, 1 row affected (0.01 sec)

DEALLOCATE prepare stmt;
Query OK, 0 rows affected (0.01 sec)

mysql> select @a;
| @a   |
|AAAA  |
1 row in set (0.01 sec)

Category: mysql Time: 2008-10-10 Views: 2
Tags: mysql dynamic

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