创建嵌套存储过程

Question

I'm using Entity Framework Core and I want to use a stored procedure. I create a custom SQL to create it on a migration.

The generate scrip is as follows:

DROP PROCEDURE IF EXISTS MigrationsScript;
DELIMITER //
CREATE PROCEDURE MigrationsScript()
BEGIN
    IF NOT EXISTS(SELECT 1 FROM `__EFMigrationsHistory` WHERE `MigrationId` = '20190411134055_AddGenerations_sp') THEN


                        DROP PROCEDURE IF EXISTS GetCurrentGeneration;
                        CREATE  PROCEDURE GetCurrentGeneration(IN timeOut INT, IN createBy char(255))
                        BEGIN
                               -- Stored procedure body
                        END
    END IF;
END //
DELIMITER ;
CALL MigrationsScript();
DROP PROCEDURE MigrationsScript;


DROP PROCEDURE IF EXISTS MigrationsScript;
DELIMITER //
CREATE PROCEDURE MigrationsScript()
BEGIN
    IF NOT EXISTS(SELECT 1 FROM `__EFMigrationsHistory` WHERE `MigrationId` = '20190411134055_AddGenerations_sp') THEN

    INSERT INTO `__EFMigrationsHistory` (`MigrationId`, `ProductVersion`)
    VALUES ('20190411134055_AddGenerations_sp', '2.2.4-servicing-10062');

    END IF;
END //
DELIMITER ;
CALL MigrationsScript();
DROP PROCEDURE MigrationsScript;

But I'm getting this error

Error Code: 1357. Can't drop or alter a PROCEDURE from within another stored routine

Answer 1

As the error message states, you can't drop or alter a procedure. Neither can you create a procedure. It is not supported by MySQL.

https://dev.mysql.com/doc/refman/8.0/en/stored-program-restrictions.html says:

Generally, statements not permitted in SQL prepared statements are also not permitted in stored programs. For a list of statements supported as prepared statements, see Section 13.5, “Prepared SQL Statement Syntax” .

You can follow that link to the documentation for SQL statements that are supported as prepared statements. But the list does not include CREATE PROCEDURE.

So you will have to create your procedure by running an SQL statement from an application or script.

Frankly, I don't use stored procedures in MySQL at all, because they're very inefficient. I understand people coming from the culture of Microsoft SQL Server or Oracle are accustomed to using stored procedures for a lot of their work, but when using MySQL, it's more common to write code in scripts in Python, Ruby, PHP, or Perl. There are better editing and debugging tools for those languages.