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I need to make a select comparing whether user login already exists or not. But I do not want to return values from the table, only a symbolic value to verify the existence (true or false). The comparison code is the basic:
SELECT * FROM USUARIOS WHERE LOGIN = '$LOGIN'
$LOGIN being the login I will compare. And select will return me all table contents unnecessarily.
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You could do it like this:
SELECT count(1) FROM USUARIOS WHERE LOGIN = '$LOGIN'
The select will return 1 find the user and 0 if not found. Similar to true and false.
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Douglas, try this:
SELECT 1 FROM USUARIOS WHERE LOGIN = '$LOGIN'
SELECT 1 it 1 if there is a record instead of the table fields, it is often used in your case, that you need to verify the existence of a record. And if it doesn’t exist, it returns nothing.
The Electus solution is good but you’ll have to make one if to check if the return was 0 or 1 and also it uses the function COUNT that will count being that you will always have only 1 record that meets the requirements soon unnecessary the use of this function, in this solution proposed by me if registration means that there is, so do not need to check.
only if you have more than 1 record it returns a certain array?
Correct! But in this specific case of it which is a login table will always be only 1 return.
The problem is that if you don’t find the user, the return of the query is empty. So he would have to use a specific function to check how many lines a query returned or if the result "is not Empty".
I assumed that I already have this check, because he in the question does not want to return columns that he will not use.
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You can do it in many ways:
select id from usuarios where login = '$LOGIN';
select count(*) from usuarios where login = '$LOGIN' limit 1;
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unnecessary the 'Count' right?
– Douglas Bernardino
No. Quite the contrary, without him the query would have only two results: 1 (if found) or empty (if not found). With the Count you can get 1 (if found) or 0 (if not found).
– electus
as I see it, the good thing about Count is that it will not return an array if it returns more than one value right?
– Douglas Bernardino
In this case you will never return more than 1 result.
– electus
can you tell me if there is a "Uppercase" in the login check = "$login"?? type, select Count(1) from usuarios Where UPPER(LOGIN) = '$LOGIN'...
– Douglas Bernardino
Yes, just use it upper(login) = upper('$LOGIN').
– electus