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Description

This error signifies that a stored function, trigger, or event is attempting to return a result set, which is not permitted in their respective contexts. Stored functions must return a single scalar value, while triggers and events cannot return any results directly.

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Error Message

Not allowed to return a result set from a %s

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Known Causes

3 known causes

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Function Returns Result Set

A `SELECT` statement without an `INTO` clause within a `FUNCTION` tries to return data. Functions must return a single scalar value, not a result set.

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Trigger Returns Result Set

A `TRIGGER` includes a `SELECT` statement that attempts to return a result set. Triggers are designed for side-effects and are not allowed to return any results.

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Event Body Result Set

An `EVENT` definition contains a `SELECT` statement that attempts to return data. Event bodies execute asynchronously and cannot directly return result sets.

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Solutions

4 solutions available

1. Remove SELECT Statement from Stored Procedure easy

The most common cause is an unintended SELECT statement returning data directly from a stored procedure.

1

Identify the stored procedure that is causing the error. You can often find this by looking at the call stack or the specific query that triggers the error.

2

Examine the stored procedure's code for any `SELECT` statements that are not part of an `INSERT`, `UPDATE`, `DELETE`, or `CALL` statement within the procedure itself. These are the statements that try to return a result set.

3

Modify the stored procedure to remove or comment out the `SELECT` statement that is returning the result set. If you need to return data, consider using `OUT` parameters or creating a separate function.

DELIMITER //

CREATE PROCEDURE my_procedure (
    IN input_param INT
    -- , OUT output_param VARCHAR(255) -- Example of OUT parameter
)
BEGIN
    -- DECLARE some_variable INT;
    -- SELECT COUNT(*) INTO some_variable FROM my_table WHERE id = input_param;
    -- SET output_param = CONCAT('Count: ', some_variable);

    -- This SELECT statement below would cause the error if not handled.
    -- SELECT * FROM another_table WHERE related_id = input_param;

    -- Instead, you might update or insert data:
    UPDATE my_table SET column_name = 'new_value' WHERE id = input_param;
END //

DELIMITER ;

4

Re-execute the stored procedure to confirm the error is resolved.

2. Use OUT Parameters for Returning Data from Stored Procedures medium

For returning single values or small datasets, use OUT parameters instead of direct SELECT statements.

1

Determine what data needs to be returned from the stored procedure. If it's a single value or a few specific values, `OUT` parameters are ideal.

2

Modify the stored procedure definition to include `OUT` parameters for the data you want to return.

DELIMITER //

CREATE PROCEDURE get_user_count (
    OUT user_count INT
)
BEGIN
    SELECT COUNT(*) INTO user_count FROM users;
END //

DELIMITER ;

3

In your application code (or another stored procedure), call the procedure and capture the `OUT` parameter's value.

SET @count = 0;
CALL get_user_count(@count);
SELECT @count AS total_users;

3. Return Result Sets from Stored Functions (if appropriate) medium

If the intent is to always return a result set, consider if a stored function is a more suitable construct.

1

Evaluate if the operation you are performing is deterministic and intended to return a value or a set of values consistently. Stored functions are designed for this.

2

If a function is appropriate, rewrite the logic from your stored procedure into a stored function, ensuring it returns a value of a defined type.

DELIMITER //

CREATE FUNCTION get_active_users_count ()
RETURNS INT
READS SQL DATA
BEGIN
    DECLARE active_count INT;
    SELECT COUNT(*) INTO active_count FROM users WHERE status = 'active';
    RETURN active_count;
END //

DELIMITER ;

3

Call the function in your queries. Note that functions can only return a single scalar value, not a full result set like a procedure can.

SELECT get_active_users_count();

4. Handle Result Sets in Client Application advanced

If the stored procedure is intended to return data, ensure your client application is prepared to receive it.

1

Verify that the client application or connector you are using supports handling multiple result sets returned from stored procedures. Most modern drivers do.

2

In your application code, iterate through the result sets returned by the stored procedure. The exact method depends on your programming language and MySQL connector library.

Example in Python with `mysql.connector`:

python
import mysql.connector

cnx = mysql.connector.connect(user='user', password='password', host='host', database='db')
cursor = cnx.cursor()

cursor.callproc('your_stored_procedure', [arg1, arg2])

# Fetch the first result set
result_set1 = cursor.fetchall()
print("Result Set 1:", result_set1)

# Check if there are more result sets and fetch them
while cursor.nextset():
    result_set = cursor.fetchall()
    print("Another Result Set:", result_set)

cursor.close()
cnx.close()

3

Ensure that the `SELECT` statements within your stored procedure are correctly structured to return the desired data, and that the procedure is designed to return one or more result sets.

DELIMITER //

CREATE PROCEDURE get_customer_and_orders (IN customer_id INT)
BEGIN
    -- First result set
    SELECT * FROM customers WHERE id = customer_id;

    -- Second result set
    SELECT * FROM orders WHERE customer_id = customer_id;
END //

DELIMITER ;

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Related Errors

5 related errors

MySQL Error 1415: Stored Routine Result Set