Kind of a Join.. IN is to retrieve if the value of a specific column lies IN a list 1,2,3,4,5 E. Select customers who lie in the following zipcodes i. When to use one over the other If we want to compare particular values in subqueries then we are using the IN keyword. 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. In general, if the selective predicate is in the subquery, then use 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. 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 in keyword. 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. I believe this has a straightforward answer. Why don't you check it from the people who developed that function in their systems?
I instead use the join operator in this manner : should-i-use-the-keyword-exists-in-sql. If you can use where in instead of where exists , then where in is probably faster. Using where in or where exists will go through all results of your parent result.
The difference here is that the where exists will cause a lot of dependet sub-queries. If you can prevent dependet sub-queries, then where in will be the better choice. Assume we have 10, companies, each has 10 users thus our users table has , entries. Now assume you want to find a user by his name or his company name. This happens, because for each user a dependent sub query is executed:. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Ask Question. Asked 13 years, 2 months ago. Article Contributed By :. Easy Normal Medium Hard Expert. Writing code in comment? Please use ide. Load Comments. What's New. Most popular in SQL. The inner query is executed only once. FROM employees emp. WHERE emp. IN: It can compare the values between sub-query and parent queries.
Whereas, IN can be used as a multiple OR operator. You can master these queries and become proficient in SQL queries by enrolling in an industry-recognized SQL certification. Is there a performance difference? Again, both query plans are the same:. There is one gotcha though. If we change EmployeeKey to be nullable, we get the following execution plans:. Quite a difference this time! The same can be seen in the IO statistics:.
When to use which operator? Some guidelines:. The same logic can be implemented with joins as well. The reason they are not included in this tip — even though they might return the exact same result set and execution plan — is because the intent is different.
With joins you merge the result sets, which means you have access to all columns of the other table. Checking for existence is more of a "side-effect".
Joins on the other hand can have multiple purposes. If you want to check for existence and if a value exist you need a column from the other table, joins are preferred. Related Articles. Delete duplicate rows with no primary key on a SQL Server table. Rolling up multiple rows into a single row and column for SQL Server data.
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