What is subquery in SQL?


A subquery is a query that is nested inside a SELECT , INSERT , UPDATE , or DELETE statement, or inside another subquery.vor 4 Tagen

What is subquery in SQL with example?

In SQL, it’s possible to place a SQL query inside another query known as subquery. For example, SELECT * FROM Customers WHERE age = ( SELECT MIN(age) FROM Customers ); Run Code. In a subquery, the outer query’s result is dependent on the result-set of the inner subquery.

What is subquery in SQL and its types?

They help us target specific rows to perform various operations in SQL. They are used to SELECT, UPDATE, INSERT and DELETE records in SQL. There are different types of SQL subquery, like Single-row subquery, multiple row subquery, multiple column subquery, correlated subquery, and nested subquery.

Why subquery is used in SQL?

A subquery is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved. Subqueries can be used with the SELECT, INSERT, UPDATE, and DELETE statements along with the operators like =, <, >, >=, <=, IN, BETWEEN, etc.

What is subquery in SQL with example?

In SQL, it’s possible to place a SQL query inside another query known as subquery. For example, SELECT * FROM Customers WHERE age = ( SELECT MIN(age) FROM Customers ); Run Code. In a subquery, the outer query’s result is dependent on the result-set of the inner subquery.

What is the syntax for subquery?

A subquery can be placed in a number of SQL clauses like WHERE clause, FROM clause, HAVING clause. You can use Subquery with SELECT, UPDATE, INSERT, DELETE statements along with the operators like =, <, >, >=, <=, IN, BETWEEN, etc. A subquery is a query within another query.

What are the two types of subqueries?

Types of Subqueries Single Row Sub Query: Sub query which returns single row output. They mark the usage of single row comparison operators, when used in WHERE conditions. Multiple row sub query: Sub query returning multiple row output. They make use of multiple row comparison operators like IN, ANY, ALL.

How many types of subquery are in SQL?

There are three broad types of a subquery in SQL. This chapter from OCA Oracle Database 11g: SQL Fundamentals I Exam Guide explains differences between a single-row subquery, multiple-row subquery and correlated subquery .

What is subquery explain?

A subquery is a query that is nested inside a SELECT , INSERT , UPDATE , or DELETE statement, or inside another subquery.

What is meant by subquery?

A subquery is a query that appears inside another query statement. Subqueries are also referred to as sub- SELECT s or nested SELECT s. The full SELECT syntax is valid in subqueries.

WHERE do we use subquery?

Subqueries can be used with SELECT, UPDATE, INSERT, DELETE statements along with expression operator. It could be equality operator or comparison operator such as =, >, =, <= and Like operator. A subquery is a query within another query. The outer query is called as main query and inner query is called as subquery.

What is the meaning of subquery?

A subquery is a query that appears inside another query statement. Subqueries are also referred to as sub- SELECT s or nested SELECT s. The full SELECT syntax is valid in subqueries.

What is difference between subquery and nested query?

When a query is included inside another query, the Outer query is known as Main Query, and Inner query is known as Subquery. In Nested Query, Inner query runs first, and only once. Outer query is executed with result from Inner query. Hence, Inner query is used in execution of Outer query.

How many types of subquery are there?

There are three broad types of a subquery in SQL. This chapter from OCA Oracle Database 11g: SQL Fundamentals I Exam Guide explains differences between a single-row subquery, multiple-row subquery and correlated subquery .

What is subquery in SQL with example?

In SQL, it’s possible to place a SQL query inside another query known as subquery. For example, SELECT * FROM Customers WHERE age = ( SELECT MIN(age) FROM Customers ); Run Code. In a subquery, the outer query’s result is dependent on the result-set of the inner subquery.

Why subquery is used in SQL?

A subquery is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved. Subqueries can be used with the SELECT, INSERT, UPDATE, and DELETE statements along with the operators like =, <, >, >=, <=, IN, BETWEEN, etc.

Is subquery executed first?

Answer: D. The sub-query always executes before the execution of the main query. Subqueries are completed first. The result of the subquery is used as input for the outer query.

How subquery is executed?

Each subquery is executed once for every row of the outer query. A correlated subquery is evaluated once for each row processed by the parent statement. The parent statement can be a SELECT, UPDATE, or DELETE statement.

Which subquery is faster?

I won’t leave you in suspense, between Joins and Subqueries, joins tend to execute faster. In fact, query retrieval time using joins will almost always outperform one that employs a subquery. The reason is that joins mitigate the processing burden on the database by replacing multiple queries with one join query.

Can subquery return multiple rows?

Multiple-row subqueries are nested queries that can return more than one row of results to the parent query. Multiple-row subqueries are used most commonly in WHERE and HAVING clauses. Since it returns multiple rows, it must be handled by set comparison operators (IN, ALL, ANY).

What are the advantages of subquery?

Advantages Of Subquery: Subqueries divide the complex query into isolated parts so that a complex query can be broken down into a series of logical steps. It is easy to understand and code maintenance is also at ease. Subqueries allow you to use the results of another query in the outer query.

What is another term for a subquery?

A subquery is also called an inner query or inner select, while the statement containing a subquery is also called an outer query or outer select.

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