I need to do a select comparing whether user login is already existent or not. But I do not want it to return me values from the table, just a symbolic value to check for existence (true or false). The comparison code is the basics:
SELECT * FROM USUARIOS WHERE LOGIN = '$LOGIN'
$ LOGIN being the login I'm going to compare. And select will return all table contents unnecessarily.
You could do this:
SELECT count(1) FROM USUARIOS WHERE LOGIN = '$LOGIN'
select will return 1 if it finds the user and 0 if it does not find it. Similar to true and false
Douglas, try this:
SELECT 1 FROM USUARIOS WHERE LOGIN = '$LOGIN'
SELECT 1 it 1 If the registry exists instead of the table fields, it is very often used in this case that you need to check for a record. And if it does not exist, it returns nothing.
The Electus solution is good, but you will have to do if to check if the return was 0 or 1 and it also uses the COUNT function that will tell you that you will always have only 1 record
You can do this in several ways:
select id from usuarios where login = '$LOGIN';
select count(*) from usuarios where login = '$LOGIN' limit 1;