In SQL Server, a subquery is a query within a query. You can create subqueries within your SQL statements. These subqueries can reside in the WHERE clause, the FROM clause, or the SELECT clause.
Why we use subquery in SQL Server?
An SQL subquery is a query inside another query. It is used in the WHERE or HAVING clause of an SQL statement. Subqueries let you specify the results of one query as an argument in another query. When you’re writing an SQL query, you may want to specify a parameter based on the result of another query.
What is an example of a subquery?
A subquery can be used anywhere an expression can be used in the SELECT clause. The following example finds the salaries of all employees, their average salary, and the difference between the salary of each employee and the average salary.
What is subquery and its types in SQL?
Type of Subqueries
Single row subquery : Returns zero or one row. Multiple row subquery : Returns one or more rows. Multiple column subqueries : Returns one or more columns. Correlated subqueries : Reference one or more columns in the outer SQL statement.
What is the difference between query and subquery?
A query is an operation that retrieves data from one or more tables or views. In this reference, a top-level SELECT statement is called a query, and a query nested within another SQL statement is called a 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 the purpose of subquery Mcq?
A subquery is a complete query nested in the SELECT, FROM, HAVING, or WHERE clause of another query. The subquery must be enclosed in parentheses and have a SELECT and a FROM clause, at a minimum. A single-row subquery can return a maximum of one value.
How do I create a subquery in SQL Server?
Subqueries in SQL Server
- You must enclose a subquery in parenthesis.
- A subquery must include a SELECT clause and a FROM clause.
- A subquery can include optional WHERE, GROUP BY, and HAVING clauses.
- A subquery cannot include COMPUTE or FOR BROWSE clauses.
What is subquery in SQL Mcq?
Explanation: A subquery is a select-from-where expression that is nested within another query.
What is subquery SQL w3schools?
Subquery or Inner query or Nested query is a query in a query. SQL subquery is usually added in the WHERE Clause of the SQL statement. Most of the time, a subquery is used when you know how to search for a value using a SELECT statement, but do not know the exact value in the database.
How do you use subqueries?
Subqueries must be enclosed within parentheses. A subquery can have only one column in the SELECT clause, unless multiple columns are in the main query for the subquery to compare its selected columns. An ORDER BY command cannot be used in a subquery, although the main query can use an ORDER BY.
How many types of subqueries are there 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 and its properties?
A subquery is a query within another query, also known as a nested query. … Properties of Sub-Query A subquery must be enclosed in the parenthesis. A subquery must be put in the right hand of the comparison operator, and A subquery cannot contain a ORDER-BY clause. A query can contain more than one sub-queries.
Why use subqueries instead of joins?
If you need to combine related information from different rows within a table, then you can join the table with itself. Use subqueries when the result that you want requires more than one query and each subquery provides a subset of the table involved in the query.
Are subqueries efficient?
If efficient indexes are available on the tables in the subquery, then a correlated subquery is likely to be the most efficient kind of subquery. If no efficient indexes are available on the tables in the subquery, then a non-correlated subquery would be likely to perform better.
How do you replace a subquery?
However, in some cases a subquery can be replaced with a more efficient JOIN. If you can avoid a subquery and replace it with a JOIN clause, you should do so without hesitation. But of course, in some cases, using a subquery is the only way to solve a data question.