A previous deployment or manual creation left the routine in place, and the CREATE statement was run again without first checking or dropping the old version The migration script was not designed to be idempotent—it lacks DROP IF EXISTS guards before CREATE statements A partially failed migration created the routine but failed later, leaving the routine in place for the next retry to collide with

Is the "1304" error serious?

It is a medium-severity error — more of a blocker than a risk. The steps above resolve it.

How to fix ERROR 1304: Stored routine already exists in MySQL

MySQLINTERMEDIATEMEDIUMUpdated Dec 25, 2025· 134 views

MySQL error 1304 (ER_SP_ALREADY_EXISTS) occurs when you try to create a stored procedure, function, trigger, or event with a name that already exists. The fix is to drop the existing routine first or use CREATE OR REPLACE on MySQL 8.0.13+.

Quick fix

Fixes 1304

SELECT ROUTINE_SCHEMA, ROUTINE_NAME, ROUTINE_TYPE
FROM INFORMATION_SCHEMA.ROUTINES
WHERE ROUTINE_NAME = 'your_procedure_name';

Verify the routine exists using INFORMATION_SCHEMA
Drop the existing routine before re-creating it
Use CREATE OR REPLACE PROCEDURE (MySQL 8.0.13+)
Guard your migration scripts with DROP IF EXISTS for idempotency

mysql — error

$SELECT ROUTINE_SCHEMA, ROUTINE_NAME, ROUTINE_TYPE
FROM INFORMATION_SCHEMA.ROUTINES
WHERE ROUTINE_NAME = 'your_procedure_name';
ERROR 1304: Stored routine already exists

What this error means

MySQL Error 1304 is raised when you attempt to create a stored routine (procedure, function, trigger, or event) using a name that already exists in the same database schema. Unlike some programming languages, MySQL does not support function overloading by parameter list—each routine name must be unique within its schema. When MySQL encounters a CREATE PROCEDURE or CREATE FUNCTION statement with a duplicate name, it immediately halts execution and returns error 1304. This is a protective measure to ensure that every reference to a routine name unambiguously points to a single definition. If the same name could refer to multiple routines, callers would have unpredictable behavior. This error is particularly common in CI/CD pipelines and automated deployments, where the same migration script may run multiple times and needs to be idempotent (safe to run repeatedly without side effects).

Typical symptoms

MySQL CLI or client returns 'ERROR 1304' immediately after running CREATE PROCEDURE or CREATE FUNCTION
Deployment or migration scripts fail at the CREATE statement and halt
Database management tools (MySQL Workbench, phpMyAdmin) report the error when attempting to create a stored procedure
Automated CI/CD pipelines fail when re-running database migration scripts without cleaning up old routines
The error message includes the routine name, e.g., 'ERROR 1304: Stored routine 'procedure_name' already exists'

Common causes

A previous deployment or manual creation left the routine in place, and the CREATE statement was run again without first checking or dropping the old version
The migration script was not designed to be idempotent—it lacks DROP IF EXISTS guards before CREATE statements
A partially failed migration created the routine but failed later, leaving the routine in place for the next retry to collide with
The script is running against the wrong database schema, hitting a name collision in the unexpected database
Routine names differ only by case (e.g., 'GetUser' vs 'getuser'), and the database is case-insensitive for identifiers

How to fix "ERROR 1304: Stored routine already exists"

1Verify the routine exists using INFORMATION_SCHEMA

Before making any changes, confirm that the routine exists and which schema it belongs to. Run:

sql

SELECT ROUTINE_SCHEMA, ROUTINE_NAME, ROUTINE_TYPE
FROM INFORMATION_SCHEMA.ROUTINES
WHERE ROUTINE_NAME = 'your_procedure_name';

This shows all routines matching the name across all schemas. Verify you're looking at the correct database.

2Drop the existing routine before re-creating it

The most straightforward fix is to drop the old routine before creating a new one. Use DROP PROCEDURE IF EXISTS (for procedures) or DROP FUNCTION IF EXISTS (for functions):

sql

DROP PROCEDURE IF EXISTS your_procedure_name;

DELIMITER //
CREATE PROCEDURE your_procedure_name()
BEGIN
    -- Your procedure body here
END //
DELIMITER ;

The IF EXISTS clause ensures the statement succeeds even if the procedure doesn't exist, making the script safe to run repeatedly (idempotent).

For functions, use:

sql

DROP FUNCTION IF EXISTS your_function_name;

DELIMITER //
CREATE FUNCTION your_function_name(param INT) RETURNS INT DETERMINISTIC READS SQL DATA
BEGIN
    -- Function body
    RETURN 0;
END //
DELIMITER ;

3Use CREATE OR REPLACE PROCEDURE (MySQL 8.0.13+)

If you're running MySQL 8.0.13 or later, you can use CREATE OR REPLACE PROCEDURE to replace the routine in a single statement without explicitly dropping it first:

sql

CREATE OR REPLACE PROCEDURE your_procedure_name()
BEGIN
    -- Your procedure body here
END //

This approach is cleaner and automatically handles the drop-and-recreate logic. Note: CREATE OR REPLACE PROCEDURE requires that parameters and return types of the new procedure are compatible with the existing one. If you're changing the signature significantly, you still need to drop and recreate.

Check your MySQL version:

sql

SELECT VERSION();

4Guard your migration scripts with DROP IF EXISTS for idempotency

To prevent this error in the future, always use DROP IF EXISTS before CREATE in deployment scripts. This makes scripts idempotent—they can be run multiple times without failure.

Example migration file:

sql

-- migration_001_create_user_procedures.sql

DROP PROCEDURE IF EXISTS get_user_by_id;
DROP PROCEDURE IF EXISTS create_user;
DROP PROCEDURE IF EXISTS delete_user;

DELIMITER //

CREATE PROCEDURE get_user_by_id(IN user_id INT)
BEGIN
    SELECT * FROM users WHERE id = user_id;
END //

CREATE PROCEDURE create_user(IN user_name VARCHAR(255), IN user_email VARCHAR(255))
BEGIN
    INSERT INTO users (name, email) VALUES (user_name, user_email);
END //

CREATE PROCEDURE delete_user(IN user_id INT)
BEGIN
    DELETE FROM users WHERE id = user_id;
END //

DELIMITER ;

Then run it safely in your CI/CD pipeline:

bash

mysql -u root -p database_name < migration_001_create_user_procedures.sql

Advanced notes

Privileges and routine recreation: When you drop a stored routine, any privileges granted specifically on that routine are also dropped. After recreating the routine, you must re-grant those privileges:

sql

GRANT EXECUTE ON PROCEDURE database_name.procedure_name TO 'user'@'host';

Case sensitivity: MySQL routines are case-insensitive by default (on case-insensitive filesystems like Windows and macOS). Ensure your CREATE statement uses the exact same case as any existing routine to avoid confusion.

Testing idempotent scripts: To verify your migration script is truly idempotent, run it twice in a test environment and confirm no errors occur on the second run: