What is a subquery in SQL?

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. Subquery must be enclosed in parentheses.

Subqueries are on the right side of the comparison operator. You can place the Subquery in a number of SQL clausesWHERE clauseHAVING clauseFROM clause.

Subqueries can be used with SELECTUPDATEINSERTDELETE statements along with expression operator. It could be equality operator or comparison operator such as =, >, =, <= and Like operator.

ORDER BY command cannot be used in a SubQueryGROUPBY command can be used to perform same function as ORDER BY command.

A Sample Syntax Example for SubQuery:

SELECT column_name

FROM table_name

WHERE column_name expression operator


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What do you mean by Table and Field in SQL?

Tables : In Relational database model, a table is a collection of data elements organised in terms of rows and columns. A table is also considered as a convenient representation of relations. Table is the most simplest form of data storage. Below is an example of an Employee table.

Tuple or Record or Row : A single entry in a table is called a Tuple or Record or Row. A tuple in a table represents a set of related data. For example, the above Employee table has 4 tuples/records/rows.

Following is an example of single record or tuple.

Fields : A field is part of a record and contains a single piece of data for the subject of the record. In the employee table, each record contains four fields. ID, Name, Age, Salary are fields in the table.

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VS Shell installation has failed with exit code 1638.

The following error has occurred:
VS Shell installation has failed with exit code 1638.

Error while installing SQL Server 2017.

Solution : Install Microsoft Visual C++ 2017 Redistributable  available at: https://go.microsoft.com/fwlink/?LinkId=746572

For any further errors please mail to contact@sqlschool.com

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