How to debug MySQL stored procedures

MySQL is a popular open source relational database management system. MySQL allows you to create and manage databases to store and access large amounts of data. Stored procedures are blocks of code stored in a database that allow you to perform common operations by calling them. When developing and debugging stored procedures, you may encounter some problems and errors. This article will introduce how to debug MySQL stored procedures.

1. Enable the MySQL stored procedure debugger

Before debugging the stored procedure, you need to enable the MySQL stored procedure debugger. This can be achieved by setting the following parameters in the MySQL configuration file:

[mysqld]
... 
# Enable stored procedure debugging 
debugger=1

After setting the file, MySQL needs to be restarted for the changes to take effect.

2. Using a debugger

In MySQL, there are two main types of debuggers: single-stepping and non-stepping. Single-step debugging is the simplest way to execute a stored procedure line by line, tracing the execution of each statement step by step. Non-stepping debugging is a method of running breakpoints while executing a stored procedure. Both debuggers are described in detail below.

3. Single-step debugging

Single-step debugging is a method of executing a stored procedure line by line. It allows you to pause and inspect your code before each statement. You can use the following steps to enable and use the single-step debugger:

1. Define a stored procedure

First, you need to define a stored procedure to demonstrate how to perform single-step debugging. The following is a simple stored procedure:

DELIMITER $$
CREATE PROCEDURE simple_addition(i INT, j INT)
BEGIN
    DECLARE result INT;
    SET result = i + j;
    SELECT result;
END$$
DELIMITER ;

2. Enable the single-step debugger

After defining the stored procedure, you need to enable the single-step debugger. You can use the following statement:

SET @@DEBUG=1;

3. Start the debugger

Next, you need to add the "debug" keyword to the stored procedure call statement to start the debugger:

CALL simple_addition(20, 30) debug;

After executing this statement, MySQL will pause execution and transfer control to the single-step debugger.

4. Using the single-step debugger

In the single-step debugger, you can use the following commands to control the execution of your code:

• c: Execute the stored procedure until execution is completed or a breakpoint is encountered
• s: Execute the stored procedure code line by line
• n: Execute the next line of code, but will not enter the subroutine or function
• p expression: print the value of the value or expression
• l: list the code of the current function or stored procedure
• b: set a breakpoint on the current line

The following is an example of using the single-step debugger:

1. Execute the stored procedure and use the debug keyword to enable the single-step debugger:

CALL simple_addition(20, 30) debug;

2. Execute the "s" command to execute the code line by line as needed.
3. When executing a row, enter "p result" to get the current data.
4. Execute the "s" command to continue executing the code.
5. Non-single-step debugging

Non-single-step debugging is a method of running breakpoints when executing a stored procedure. You can use the following steps to enable and use the non-single-stepping debugger:

1. Define a stored procedure

Again, you need to first define a stored procedure to demonstrate how to non-single-step debug. The following is a simple stored procedure:

DELIMITER $$
CREATE PROCEDURE simple_subtraction(i INT, j INT)
BEGIN
    DECLARE result INT;
    SET result = i - j;
    SELECT result;
END$$
DELIMITER ;

2. Enable non-single-step debugger

You can use the following command to enable the non-single-step debugger:

CALL simple_subtraction(20, 30) debug_on_break;

When executing a stored procedure, if a breakpoint is encountered, MySQL will automatically stop execution.

3. Using Non-Single-Step Debugging

Once the non-single-step debugger is enabled, you can use the following commands to control the execution of your code:

• c: Execute the stored procedure until execution is complete or a breakpoint is encountered
• b: Set a breakpoint on the current line
• r: Restart the stored procedure
• p expression :Print the value of a value or expression

Here is an example using a non-single-step debugger:

1. Execute the stored procedure and set a breakpoint on line 3 :

CALL simple_subtraction(20, 30) debug_on_break(3);

2. Execute the stored procedure until a breakpoint is encountered:

c;

3. Print the value of the "result" variable:

p result;

4. Delete breakpoint:

b -3;

5. Restart stored procedure:

r;

4. Summary

MySQL provides a variety of methods for debugging stored procedures, including single-step debugging and non-single-step debugging. When using these debuggers, you can use various commands to control the execution of your code and view the values ​​of variables and expressions. If you are developing a complex stored procedure, these debuggers can be very useful tools.

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