In case you don't need to tell the original user when the record was changed by another user, you can just grab the old value in the SELECT, perform the UPDATE by including the old value in the WHERE clause, and check the result: If it didn't work or you don't get the new value when SELECTing the row, it means that someone else has updated this row while you were busy.
Here's an example in SQLite:
===
CREATE TABLE IF NOT EXISTS mytable (id INTEGER PRIMARY KEY, label VARCHAR);
INSERT INTO mytable (label) VALUES ("old");//Some other user updates this row while you're busy
UPDATE mytable SET label="concurrency" WHERE id=1;
UPDATE mytable SET label="new" WHERE id=1 AND label="old";//In case your DBMS doesn't return a value so you can tell if it went OK or not,//just reread the row:
SELECT label FROM mytable;
concurrency
===
HTH,
Slashdot Mirror
In case you don't need to tell the original user when the record was changed by another user, you can just grab the old value in the SELECT, perform the UPDATE by including the old value in the WHERE clause, and check the result: If it didn't work or you don't get the new value when SELECTing the row, it means that someone else has updated this row while you were busy. Here's an example in SQLite: === CREATE TABLE IF NOT EXISTS mytable (id INTEGER PRIMARY KEY, label VARCHAR); INSERT INTO mytable (label) VALUES ("old"); //Some other user updates this row while you're busy
UPDATE mytable SET label="concurrency" WHERE id=1;
UPDATE mytable SET label="new" WHERE id=1 AND label="old"; //In case your DBMS doesn't return a value so you can tell if it went OK or not, //just reread the row:
SELECT label FROM mytable;
concurrency
===
HTH,