What is the difference between the
IN clause in SQL?
When should we use
EXISTS, and when should we use
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~ Asked on 2008-08-24 08:42:23
exists keyword can be used in that way, but really it's intended as a way to avoid counting:
--this statement needs to check the entire table select count(*) from [table] where ... --this statement is true as soon as one match is found exists ( select * from [table] where ... )
This is most useful where you have
if conditional statements, as
exists can be a lot quicker than
in is best used where you have a static list to pass:
select * from [table] where [field] in (1, 2, 3)
When you have a table in an
in statement it makes more sense to use a
join, but mostly it shouldn't matter. The query optimiser should return the same plan either way. In some implementations (mostly older, such as Microsoft SQL Server 2000)
in queries will always get a nested join plan, while
join queries will use nested, merge or hash as appropriate. More modern implementations are smarter and can adjust the plan even when
in is used.
~ Answered on 2008-08-24 09:37:52
EXISTS will tell you whether a query returned any results. e.g.:
SELECT * FROM Orders o WHERE EXISTS ( SELECT * FROM Products p WHERE p.ProductNumber = o.ProductNumber)
IN is used to compare one value to several, and can use literal values, like this:
SELECT * FROM Orders WHERE ProductNumber IN (1, 10, 100)
You can also use query results with the
IN clause, like this:
SELECT * FROM Orders WHERE ProductNumber IN ( SELECT ProductNumber FROM Products WHERE ProductInventoryQuantity > 0)
~ Answered on 2008-08-24 08:47:45
Based on rule optimizer:
EXISTSis much faster than
IN, when the sub-query results is very large.
INis faster than
EXISTS, when the sub-query results is very small.
Based on cost optimizer:
~ Answered on 2010-10-19 01:35:32
I'm assuming you know what they do, and thus are used differently, so I'm going to understand your question as: When would it be a good idea to rewrite the SQL to use IN instead of EXISTS, or vice versa.
Is that a fair assumption?
Edit: The reason I'm asking is that in many cases you can rewrite an SQL based on IN to use an EXISTS instead, and vice versa, and for some database engines, the query optimizer will treat the two differently.
SELECT * FROM Customers WHERE EXISTS ( SELECT * FROM Orders WHERE Orders.CustomerID = Customers.ID )
can be rewritten to:
SELECT * FROM Customers WHERE ID IN ( SELECT CustomerID FROM Orders )
or with a join:
SELECT Customers.* FROM Customers INNER JOIN Orders ON Customers.ID = Orders.CustomerID
So my question still stands, is the original poster wondering about what IN and EXISTS does, and thus how to use it, or does he ask wether rewriting an SQL using IN to use EXISTS instead, or vice versa, will be a good idea?
~ Answered on 2008-08-24 08:45:39
EXISTS is much faster than
IN when the subquery results is very large.
IN is faster than
EXISTS when the subquery results is very small.
CREATE TABLE t1 (id INT, title VARCHAR(20), someIntCol INT) GO CREATE TABLE t2 (id INT, t1Id INT, someData VARCHAR(20)) GO INSERT INTO t1 SELECT 1, 'title 1', 5 UNION ALL SELECT 2, 'title 2', 5 UNION ALL SELECT 3, 'title 3', 5 UNION ALL SELECT 4, 'title 4', 5 UNION ALL SELECT null, 'title 5', 5 UNION ALL SELECT null, 'title 6', 5 INSERT INTO t2 SELECT 1, 1, 'data 1' UNION ALL SELECT 2, 1, 'data 2' UNION ALL SELECT 3, 2, 'data 3' UNION ALL SELECT 4, 3, 'data 4' UNION ALL SELECT 5, 3, 'data 5' UNION ALL SELECT 6, 3, 'data 6' UNION ALL SELECT 7, 4, 'data 7' UNION ALL SELECT 8, null, 'data 8' UNION ALL SELECT 9, 6, 'data 9' UNION ALL SELECT 10, 6, 'data 10' UNION ALL SELECT 11, 8, 'data 11'
SELECT FROM t1 WHERE not EXISTS (SELECT * FROM t2 WHERE t1.id = t2.t1id)
SELECT t1.* FROM t1 WHERE t1.id not in (SELECT t2.t1id FROM t2 )
t1 your id has null value then Query 1 will find them, but Query 2 cant find null parameters.
IN can't compare anything with null, so it has no result for null, but
EXISTS can compare everything with null.
~ Answered on 2012-07-04 12:40:45
If you are using the
IN operator, the SQL engine will scan all records fetched from the inner query. On the other hand if we are using
EXISTS, the SQL engine will stop the scanning process as soon as it found a match.
~ Answered on 2013-07-16 08:00:48
IN supports only equality relations (or inequality when preceded by NOT).
It is a synonym to =any / =some, e.g
select * from t1 where x in (select x from t2) ;
EXISTS supports variant types of relations, that cannot be expressed using IN, e.g. -
select * from t1 where exists (select null from t2 where t2.x=t1.x and t2.y>t1.y and t2.z like '?' || t1.z || '?' ) ;
The allegedly performance and technical differences between EXISTS and IN may result from specific vendor's implementations/limitations/bugs, but many times they are nothing but myths created due to lack of understanding of the databases internals.
The tables' definition, statistics' accuracy, database configuration and optimizer's version have all impact on the execution plan and therefore on the performance metrics.
~ Answered on 2016-10-07 13:46:27
Exists keyword evaluates true or false, but
IN keyword compare all value in the corresponding sub query column.
Select 1 can be use with
Exists command. Example:
SELECT * FROM Temp1 where exists(select 1 from Temp2 where conditions...)
IN is less efficient so
~ Answered on 2012-05-25 05:00:44
EXISTS is when you need to match the results of query with another subquery.
Query#1 results need to be retrieved where SubQuery results match. Kind of a Join..
E.g. select customers table#1 who have placed orders table#2 too
IN is to retrieve if the value of a specific column lies
IN a list (1,2,3,4,5)
E.g. Select customers who lie in the following zipcodes i.e. zip_code values lies in (....) list.
When to use one over the other... when you feel it reads appropriately (Communicates intent better).
~ Answered on 2008-08-24 08:50:31
Difference lies here:
select * from abcTable where exists (select null)
Above query will return all the records while below one would return empty.
select * from abcTable where abcTable_ID in (select null)
Give it a try and observe the output.
~ Answered on 2015-05-19 12:42:56
The reason is that the EXISTS operator works based on the “at least found” principle. It returns true and stops scanning table once at least one matching row found.
On the other hands, when the IN operator is combined with a subquery, MySQL must process the subquery first, and then uses the result of the subquery to process the whole query.
The general rule of thumb is that if the subquery contains a large volume of data, the EXISTS operator provides a better performance.
However, the query that uses the IN operator will perform faster if the result set returned from the subquery is very small.
~ Answered on 2016-04-07 09:04:10
Which one is faster depends on the number of queries fetched by the inner query:
EXIST evaluate on true or false but IN compare multiple value. When you don't know the record is exist or not, your should choose EXIST
~ Answered on 2013-07-04 07:08:17
As per my knowledge when a subquery returns a
NULL value then the whole statement becomes
NULL. In that cases we are using the
EXITS keyword. If we want to compare particular values in subqueries then we are using the
~ Answered on 2012-03-21 02:01:15
My understand is both should be the same as long as we are not dealing with NULL values.
The same reason why the query does not return the value for = NULL vs is NULL. http://sqlinthewild.co.za/index.php/2010/02/18/not-exists-vs-not-in/
As for as boolean vs comparator argument goes, to generate a boolean both values needs to be compared and that is how any if condition works.So i fail to understand how IN and EXISTS behave differently .
~ Answered on 2016-09-12 22:02:00
In certain circumstances, it is better to use IN rather than EXISTS. In general, if the selective predicate is in the subquery, then use IN. If the selective predicate is in the parent query, then use EXISTS.
~ Answered on 2017-08-17 14:10:53
~ Answered on 2020-06-23 14:59:04
I found that using EXISTS keyword is often really slow (that is very true in Microsoft Access). I instead use the join operator in this manner : should-i-use-the-keyword-exists-in-sql
~ Answered on 2017-06-27 14:54:58
I believe this has a straightforward answer. Why don't you check it from the people who developed that function in their systems?
If you are a MS SQL developer, here is the answer directly from Microsoft.
Determines whether a specified value matches any value in a subquery or a list.
Specifies a subquery to test for the existence of rows.
~ Answered on 2017-03-24 05:01:10
If a subquery returns more than one value, you might need to execute the outer query- if the values within the column specified in the condition match any value in the result set of the subquery. To perform this task, you need to use the
You can use a subquery to check if a set of records exists. For this, you need to use the
exists clause with a subquery. The
exists keyword always return true or false value.
~ Answered on 2012-12-04 11:24:04
EXISTS Is Faster in Performance than IN. If Most of the filter criteria is in subquery then better to use IN and If most of the filter criteria is in main query then better to use EXISTS.
~ Answered on 2013-04-09 19:03:43
If you are using the IN operator, the SQL engine will scan all records fetched from the inner query. On the other hand if we are using EXISTS, the SQL engine will stop the scanning process as soon as it found a match.
~ Answered on 2012-06-04 01:43:38