ʞɔıu ʞɔıu - 7 months ago 15
SQL Question

Create function through MySQLdb

How can I define a multi-statement function or procedure in using the MySQLdb lib in python?

Example:

import MySQLdb

db = MySQLdb.connect(db='service')

c = db.cursor()

c.execute("""DELIMITER //
CREATE FUNCTION trivial_func (radius float)
RETURNS FLOAT

BEGIN
IF radius > 1 THEN
RETURN 0.0;
ELSE
RETURN 1.0;
END IF;
END //

DELIMITER ;""")


Which creates the following traceback:

Traceback (most recent call last):
File "proof.py", line 21, in <module>
DELIMITER ;""")
File "build/bdist.macosx-10.5-i386/egg/MySQLdb/cursors.py", line 173, in execute
File "build/bdist.macosx-10.5-i386/egg/MySQLdb/connections.py", line 35, in defaulterrorhandler
_mysql_exceptions.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DELIMITER //\nCREATE FUNCTION trivial_func (radius float) \n RETURNS FLOAT\n\n ' at line 1")


If I copy the same SQL directly into a mysql shell client, it works as expected

Answer

The DELIMITER command is a MySQL shell client builtin, and it's recognized only by that program (and MySQL Query Browser). It's not necessary to use DELIMITER if you execute SQL statements directly through an API.

The purpose of DELIMITER is to help you avoid ambiguity about the termination of the CREATE FUNCTION statement, when the statement itself can contain semicolon characters. This is important in the shell client, where by default a semicolon terminates an SQL statement. You need to set the statement terminator to some other character in order to submit the body of a function (or trigger or procedure).

CREATE FUNCTION trivial_func (radius float) 
    RETURNS FLOAT

    BEGIN
    IF radius > 1 THEN
        RETURN 0.0; <-- does this semicolon terminate RETURN or CREATE FUNCTION?
    ELSE
        RETURN 1.0;
    END IF;
END

Since the API typically allows you to submit one SQL statement at a time, there's no ambiguity -- the interface knows that any semicolons inside the body of your function definition don't terminate the whole CREATE FUNCTION statement. So there's no need to change the statement terminator with DELIMITER.

Comments