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What is the difference between the EXISTS and IN clause in SQL?
When should we use EXISTS, and when should we use IN?
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The Exist operators are used to check sub- query condition if it satisfies all condition then exist operator provide true result , however In operator is used for adding multiple or queries. “Exists” lets you compare more values between the tables than just seeing if a key matches. “In” is faster to write and gives you a simpler-looking query.
IN works faster than the EXISTS Operator when If the sub-query result is small. If the sub-query result is larger, then EXISTS works faster than the IN Operator. 3. In the IN-condition SQL Engine compares all the values in the IN Clause. Once true is evaluated in the EXISTS condition then the SQL Engine will stop the process of further matching. 4.
In the IN-condition SQL Engine compares all the values in the IN Clause. Once true is evaluated in the EXISTS condition then the SQL Engine will stop the process of further matching.
The EXISTS operator doesn't check for values, but instead checks for the existence of rows. Typically, a subquery is used in conjunction with EXISTS.
The 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 count.
The 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.
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