EXECUTE IMMEDIATE

Syntax

EXECUTE IMMEDIATE statement
    [USING param[, param] ...]

param:
    expression | IGNORE | DEFAULT

Description

EXECUTE IMMEDIATE executes a dynamic SQL statement created on the fly, which can reduce performance overhead.

For example:

EXECUTE IMMEDIATE 'SELECT 1'

which is shorthand for:

prepare stmt from "select 1";
execute stmt;
deallocate prepare stmt;

EXECUTE IMMEDIATE supports complex expressions as prepare source and parameters:

EXECUTE IMMEDIATE CONCAT('SELECT COUNT(*) FROM ', 't1', ' WHERE a=?') USING 5+5;

Limitations: subselects and stored function calls are not supported as a prepare source.

The following examples return an error:

CREATE OR REPLACE FUNCTION f1() RETURNS VARCHAR(64) RETURN 'SELECT * FROM t1';
EXECUTE IMMEDIATE f1();
ERROR 1970 (42000): EXECUTE IMMEDIATE does not support subqueries or stored functions

EXECUTE IMMEDIATE (SELECT 'SELECT * FROM t1');
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that 
  corresponds to your MariaDB server version for the right syntax to use near 
  'SELECT 'SELECT * FROM t1')' at line 1

CREATE OR REPLACE FUNCTION f1() RETURNS INT RETURN 10;
EXECUTE IMMEDIATE 'SELECT * FROM t1 WHERE a=?' USING f1();
ERROR 1970 (42000): EXECUTE..USING does not support subqueries or stored functions

EXECUTE IMMEDIATE 'SELECT * FROM t1 WHERE a=?' USING (SELECT 10);
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that 
  corresponds to your MariaDB server version for the right syntax to use near 
  'SELECT 10)' at line 1

One can use a user or an SP variable as a workaround:

CREATE OR REPLACE FUNCTION f1() RETURNS VARCHAR(64) RETURN 'SELECT * FROM t1';
SET @stmt=f1();
EXECUTE IMMEDIATE @stmt;

SET @stmt=(SELECT 'SELECT 1');
EXECUTE IMMEDIATE @stmt;

CREATE OR REPLACE FUNCTION f1() RETURNS INT RETURN 10;
SET @param=f1();
EXECUTE IMMEDIATE 'SELECT * FROM t1 WHERE a=?' USING @param;

SET @param=(SELECT 10);
EXECUTE IMMEDIATE 'SELECT * FROM t1 WHERE a=?' USING @param;

EXECUTE IMMEDIATE supports user variables and SP variables as OUT parameters

DELIMITER $$
CREATE OR REPLACE PROCEDURE p1(OUT a INT)
BEGIN
  SET a:= 10;
END;
$$
DELIMITER ;
SET @a=2;
EXECUTE IMMEDIATE 'CALL p1(?)' USING @a;
SELECT @a;
+------+
| @a   |
+------+
|   10 |
+------+

Similar to PREPARE, EXECUTE IMMEDIATE is allowed in stored procedures but is not allowed in stored functions.

This example uses EXECUTE IMMEDIATE inside a stored procedure:

DELIMITER $$
CREATE OR REPLACE PROCEDURE p1()
BEGIN
  EXECUTE IMMEDIATE 'SELECT 1';
END;
$$
DELIMITER ;
CALL p1;
+---+
| 1 |
+---+
| 1 |
+---+

This script returns an error:

DELIMITER $$
CREATE FUNCTION f1() RETURNS INT
BEGIN
  EXECUTE IMMEDIATE 'DO 1';
  RETURN 1;
END;
$$
ERROR 1336 (0A000): Dynamic SQL is not allowed in stored function or trigger

EXECUTE IMMEDIATE can use DEFAULT and IGNORE indicators as bind parameters:

CREATE OR REPLACE TABLE t1 (a INT DEFAULT 10);
EXECUTE IMMEDIATE 'INSERT INTO t1 VALUES (?)' USING DEFAULT;
SELECT * FROM t1;
+------+
| a    |
+------+
|   10 |
+------+

EXECUTE IMMEDIATE increments the Com_execute_immediate status variable, as well as the Com_stmt_prepare, Com_stmt_execute and Com_stmt_close status variables.

Note, EXECUTE IMMEDIATE does not increment the Com_execute_sql status variable. Com_execute_sql is used only for PREPARE..EXECUTE.

This session screenshot demonstrates how EXECUTE IMMEDIATE affects status variables:

SELECT * FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME RLIKE 
  ('COM_(EXECUTE|STMT_PREPARE|STMT_EXECUTE|STMT_CLOSE)');

+-----------------------+----------------+
| VARIABLE_NAME         | VARIABLE_VALUE |
+-----------------------+----------------+
| COM_EXECUTE_IMMEDIATE | 0              |
| COM_EXECUTE_SQL       | 0              |
| COM_STMT_CLOSE        | 0              |
| COM_STMT_EXECUTE      | 0              |
| COM_STMT_PREPARE      | 0              |
+-----------------------+----------------+

EXECUTE IMMEDIATE 'SELECT 1';
+---+
| 1 |
+---+
| 1 |
+---+

SELECT * FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME RLIKE 
  ('COM_(EXECUTE|STMT_PREPARE|STMT_EXECUTE|STMT_CLOSE)');
+-----------------------+----------------+
| VARIABLE_NAME         | VARIABLE_VALUE |
+-----------------------+----------------+
| COM_EXECUTE_IMMEDIATE | 1              |
| COM_EXECUTE_SQL       | 0              |
| COM_STMT_CLOSE        | 1              |
| COM_STMT_EXECUTE      | 1              |
| COM_STMT_PREPARE      | 1              |
+-----------------------+----------------+

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