What are subqueries in SQL?
A Subquery or Inner query or a Nested query is a query within another SQL query and embedded within the WHERE clause. 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. A subquery cannot be immediately enclosed in a set function.
How subquery works in SQL?
In SQL a Subquery can be simply defined as a query within another query. A subquery is a query within another query. The outer query is called as main query and inner query is called as subquery. The subquery generally executes first, and its output is used to complete the query condition for the main or outer query.
What is trigger in SQL?
A SQL trigger is a database object which fires when an event occurs in a database. We can execute a SQL query that will “do something” in a database when a change occurs on a database table such as a record is inserted or updated or deleted. For example, a trigger can be set on a record insert in a database table.
Why do we use subquery?
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 subquery and its types?
Types of Subqueries Single Row Sub Query: Sub query which returns single row output. Multiple row sub query: Sub query returning multiple row output. They make use of multiple row comparison operators like IN, ANY, ALL. There can be sub queries returning multiple columns also.
What does colon mean in SQL?
The colon (:) is used to select “slices” from arrays. (See Section 5.12.) In certain SQL dialects (such as Embedded SQL), the colon is used to prefix variable names. The asterisk (*) has a special meaning when used in the SELECT command or with the COUNT aggregate function.
Why do we use subqueries in SQL?
SQL Subquery: A Guide An SQL subquery is a query within another query. They are used to run a query that depends on the results of another query. Subqueries let you do this without having to write two separate queries and copy-paste the results.