SELECT * (Database Weekly 11.02.2008) – Learn more on the SQLServerCentral forums Typically this is an area where it’s been instilled in me to use SELECT 1 instead of SELECT * for performance reasons. Actual Difference Between EXISTS(SELECT 1 …), EXISTS(SELECT * …), and EXISTS(SELECT column …) On the other hand, when you use JOINS you might not get the same result set as in the IN and the EXISTS clauses.

It does not matter if the row is NULL or not.. The latest blog posts on SQLServerCentral. However, is it a myth or is it reality that SELECT * vs.

EXISTS Subqueries: SELECT 1 vs. SQL EXISTS and NULL.

There should be no difference (in theory) Although the second query reads like it will return many more rows than the "top 1" query, the reality is that is not how EXISTS should work.The inner subquery does NOT need to return any data whatsoever, all that matters IS THERE A ROW, and as soon as THERE IS A ROW the exists condition is met. If the subquery returns NULL, the EXISTS operator still returns the result set. Most of the time, IN and EXISTS give you the same results with the same performance. SQL> declare 2 v_cnt number; 3 begin 4 my_pack.v_a := 'Not Found'; 5 select count(1) into v_cnt from dual where 6 text_call = 1 and 1=2; 7 dbms_output.put_line(my_pack.v_a); 8 end; 9 / Not Found PL/SQL procedure successfully completed. Powyższe zapytanie zwraca nam departamenty z tabeli departments w których pracuje jakikolwiek pracownik.

In the following example, the subquery returns NULL but the EXISTS operator still evaluates to true:. 1. SELECT col1 FROM MyTable WHERE EXISTS (SELECT * FROM Table2 WHERE MyTable.col1=Table2.col2) The * will be expanded to some potentially big column list and then it will be determined that the semantics of the EXISTS does not require any of those columns, so basically all of them can be removed. W podzapytaniu występuje warunek where e.department_id=d.department_id , określający zasadę według której system poszukuje odpowiedników w podzbiorze.

SELECT 1 will make an impact to performance when used in the EXISTS logical operator? So, to optimize performance, you need to be smart in using and selecting which one of the operators. EXISTS vs IN vs JOIN with NOT NULLable columns:

IIRC, 1 and * do exactly the same thing in exists because exists doesn't actually return data, it merely verifies the existence of a row matching criteria, so your select is more or less ignored. no points pl. This is because the EXISTS operator only checks for the existence of row returned by the subquery. Often, I see in articles and code a query using the EXISTS logical operator and a Subquery within the EXISTS using SELECT *.