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SQL Subqueries
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SQL Subqueries are the nested queries, there will be one main query inside that, we might have one or more subqueries.
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subqueries are called as inner queries.
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mainqueries are called as outer queries.
Subqueries - IN Clause
Syntax
SELECT
*
FROM
table_1 t1
WHERE
column_name in (inner_query or subquery)
Subqueries - EXISTS Clause
Syntax
SELECT
*
FROM
table_1 t1
WHERE
EXISTS (inner_query or subquery)
IN Clause
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It search among the list.
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It is faster for smaller data.
EXISTS Clause
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It checks for the existence.
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It is faster for larger amount of data.
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All the above queries which we can write using subqueries can be written using joins as well.
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Sometimes it is efficient to use join and sometimes it is good to use subqueries. with time we will understand when to use joins and when to use subqueries.
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