How to View a Stored Procedure in MySQL Server

Stored procedures are a powerful feature in MySQL, allowing you to encapsulate complex SQL logic into reusable routines. Sometimes, especially for debugging or understanding existing database structures, you need to examine the internal implementation of these stored procedures. MySQL provides the SHOW PROCEDURE CODE statement to help you achieve this. This article will guide you through how to use this statement to view the code of a stored procedure in your MySQL server.

Understanding the `SHOW PROCEDURE CODE` Statement

The SHOW PROCEDURE CODE statement is a MySQL extension designed for servers built with debugging support. It allows you to inspect a representation of the internal implementation of a given stored procedure. It’s similar to SHOW FUNCTION CODE, which serves the same purpose for stored functions.

This statement is invaluable for:

Debugging: Understanding the execution flow and internal logic of a stored procedure when troubleshooting issues.
Code Review: Examining existing stored procedures to understand their functionality and potential areas for improvement.
Learning: Gaining insights into how MySQL internally handles stored procedure definitions.

Syntax

The syntax for the SHOW PROCEDURE CODE statement is straightforward:

SHOW PROCEDURE CODE procedure_name;

Here, procedure_name is the name of the stored procedure you want to inspect. Make sure to specify the correct procedure name, including the database name if the procedure is not in the current database. For example, if your procedure my_procedure is in the database mydatabase, you would use mydatabase.my_procedure.

Required Privileges

To execute SHOW PROCEDURE CODE, you need to have sufficient privileges. You must be one of the following:

The user named as the DEFINER of the stored procedure.
A user with the SHOW_ROUTINE privilege.
A user with the global SELECT privilege.

Without these privileges, you will not be able to view the code of the stored procedure.

Interpreting the Output

When executed successfully, SHOW PROCEDURE CODE returns a result set. Each row in this result set represents a single “instruction” in the internal implementation of the stored procedure. The result set contains two columns:

Pos: This is an ordinal number, starting from 0, indicating the position of the instruction in the sequence.
Instruction: This column contains the actual instruction. It can be an SQL statement (often modified from the original source code) or a directive specific to the stored-routine handler.

Let’s look at an example to understand this better.

Example

Consider the following stored procedure:

DELIMITER //
CREATE PROCEDURE p1 ()
BEGIN
  DECLARE fanta INT DEFAULT 55;
  DROP TABLE IF EXISTS t2;
  CREATE TABLE IF NOT EXISTS t3 (id INT);
  LOOP
    INSERT INTO t3 VALUES (fanta);
  END LOOP;
END//
DELIMITER ;

This procedure p1 declares a variable, drops a table (if it exists), creates another table (if it doesn’t exist), and then enters an infinite loop inserting a value.

Now, let’s use SHOW PROCEDURE CODE to view its internal representation:

SHOW PROCEDURE CODE p1;

The output might look like this:

+-----+------------------------------------------------+
| Pos | Instruction                                    |
+-----+------------------------------------------------+
| 0   | set fanta@0 55                                 |
| 1   | stmt 9 "DROP TABLE IF EXISTS t2"                 |
| 2   | stmt 9 "CREATE TABLE IF NOT EXISTS t3 (id INT)" |
| 3   | stmt 5 "INSERT INTO t3 VALUES (fanta)"          |
| 4   | jump 3                                         |
+-----+------------------------------------------------+

Explanation of the output:

Pos 0: set fanta@0 55: This instruction corresponds to the declaration and initialization of the variable fanta. Note that @0 is an internal representation of the variable.
Pos 1: stmt 9 "DROP TABLE IF EXISTS t2": This represents the DROP TABLE IF EXISTS t2 statement. stmt 9 indicates that this is a DROP TABLE statement (the number 9 is an internal statement type code).
Pos 2: stmt 9 "CREATE TABLE IF NOT EXISTS t3 (id INT)": Similarly, this represents the CREATE TABLE IF NOT EXISTS t3 (id INT) statement, also identified as statement type 9.
Pos 3: stmt 5 "INSERT INTO t3 VALUES (fanta)": This is the INSERT statement within the loop. stmt 5 indicates an INSERT statement.
Pos 4: jump 3: This jump instruction represents the loop’s control flow. It tells the execution to jump back to instruction number 3 (the INSERT statement), creating the infinite loop.

Notice that non-executable statements like BEGIN and END from the original procedure definition are not present in the SHOW PROCEDURE CODE output. Also, for statements taken directly from the source, you’ll see the stmt keyword followed by a type number and the SQL statement itself in quotes.

Important Considerations

Debugging Builds: SHOW PROCEDURE CODE is only available on MySQL servers compiled with debugging support. Standard production builds might not include this feature.
Internal Representation: The output of SHOW PROCEDURE CODE is an internal representation of the procedure’s logic, not necessarily the exact source code you wrote. Some transformations or simplifications might occur.
Statement Types: The statement type numbers (like 9 for DROP TABLE and CREATE TABLE, and 5 for INSERT) are internal MySQL codes and might not be officially documented or stable across different MySQL versions.

Conclusion

The SHOW PROCEDURE CODE statement is a valuable tool for MySQL developers and administrators who need to delve into the inner workings of stored procedures. By understanding how to use this statement and interpret its output, you can gain deeper insights into your database logic, facilitate debugging, and improve your overall understanding of MySQL stored procedures. Remember to check your privileges and use this feature responsibly, especially in production environments.