How to Use Dynamic SQL in MySQL Stored Procedures?

Dynamic SQL in MySQL Stored Procedures

MySQL versions 5.0.13 and later provide the ability to construct and execute dynamic SQL statements within stored procedures. This allows for greater flexibility and customization in your database operations.

How to Construct Dynamic SQL in a Stored Procedure

To build dynamic SQL, you can use the following steps:

1. Create a string variable to store the SQL statement.
2. Use the CONCAT() function to dynamically construct the SQL statement based on input parameters or other variables.
3. Prepare the SQL statement using the PREPARE statement.
4. Execute the prepared statement using the EXECUTE statement.
5. Deallocate the prepared statement using the DEALLOCATE PREPARE statement.

Example:

Consider the following stored procedure that selects a column from a table based on user-provided inputs:

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

To use the stored procedure, you can call it with the desired table and column names as follows:

CALL dynamic('customers', 'name');

This will execute the following SQL statement:

SELECT name FROM customers;

Note:

• Dynamic SQL is not supported in functions or triggers.
• It is important to handle potential security risks associated with dynamic SQL by ensuring proper user input validation and sanitization.

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