Delete rows from 2 tables using a single query - sql

Question

I have the following database-schema:
I have the following example data:
CREATE TABLE computermapping (
ComputerMappingID int NOT NULL,
PrinterGUID char(36) NOT NULL,
ComputerGUID char(36) NOT NULL
);
INSERT INTO computermapping (ComputerMappingID, PrinterGUID, ComputerGUID) VALUES
(1, 'PRT01', 'Computer1'),
(2, 'PRT02', 'Computer1'),
(3, 'PRT01', 'Computer2'),
(4, 'PRT02', 'Computer2'),
(5, 'PRT03', 'Computer2'),
(6, 'PRT01', 'Computer3');
CREATE TABLE computerdefaultprinter (
ComputerGUID char(36) NOT NULL,
PrinterGUID char(36) NOT NULL
);
INSERT INTO computerdefaultprinter (ComputerGUID, PrinterGUID) VALUES
('Computer2', 'PRT01'),
('Computer1', 'PRT02');
Remark: Originally the tables are full of GUIDs, but I replaced them by names just for better readability.
I have also created an SQL-Fiddle with some example-data: Link
.
Taking the example data, I want to remove the printer "PRT01" from computer "Computer2".
I need to delete the appropriate row in the table computermapping and I need to delete the appropriate row in the table computerdefaultprinter. I want to delete the mentioned data in BOTH tables using ONE SINGLE statement.
According to my program-code I need to target the data by using NOT IN().
Till now I successfully used 2 statements joined/glued together by ";":
DELETE FROM computermapping WHERE PrinterGUID = 'PRT01' AND ComputerGUID NOT IN ('Computer1','Computer3');
DELETE FROM computerdefaultprinter WHERE PrinterGUID = 'PRT01' AND ComputerGUID NOT IN ('Computer1','Computer3')
This was working fine using MySQL, but it is not working with Microsoft SQL-Server. Yes, it does using the SQL Server Management Studio, but not programmatically. (count field incorrect or syntax error)
I am looking for a different approach for this task.
I did a research and it was mentioned, that it should be possible to delete the rows in both tables using "INNER JOIN", but I wasn't able to get it working and I am looking for help.
Thank you

Answer 1

You can add a foreign key with ON DELETE CASCADE.
For example:
CREATE TABLE computermapping (
ComputerMappingID int NOT NULL,
PrinterGUID char(36) NOT NULL,
ComputerGUID char(36) NOT NULL,
primary key (ComputerGUID, PrinterGUID)
);
INSERT INTO computermapping (ComputerMappingID, PrinterGUID, ComputerGUID) VALUES
(1, 'PRT01', 'Computer1'),
(2, 'PRT02', 'Computer1'),
(3, 'PRT01', 'Computer2'),
(4, 'PRT02', 'Computer2'),
(5, 'PRT03', 'Computer2'),
(6, 'PRT01', 'Computer3');
CREATE TABLE computerdefaultprinter (
ComputerGUID char(36) NOT NULL,
PrinterGUID char(36) NOT NULL,
foreign key (ComputerGUID, PrinterGUID)
references computermapping (ComputerGUID, PrinterGUID)
on delete cascade
);
INSERT INTO computerdefaultprinter (ComputerGUID, PrinterGUID) VALUES
('Computer2', 'PRT01'),
('Computer1', 'PRT02');
delete from computermapping
where PrinterGUID = 'PRT01' and ComputerGUID = 'Computer2';
The DELETE deletes a row in computermapping and all related rows from computerdefaultprinter as well.
See running example at SQL Fiddle.