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Issue 20.3 ('XDC Anywhere')
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SQL Subqueries

Queries within queries

Issue: 20.3 (May/June 2022)
Author: Vince Du Beau
Author Bio: Vince is an experienced Filemaker developer. He is exploring XOJO as an alternative to Filemaker.
Article Description: No description available.
Article Length (in bytes): 5,504
Starting Page Number: 84
Article Number: 20310
Related Link(s): None

Excerpt of article text...

A subquery is a SELECT within another SQL statement. They are also know as an inner query or nested query. They can be used with SELECTs, INSERTs, UPDATEs, and DELETEs. Here I have only used it within another SELECT statement.

The following rules for subqueries are from https://www.tutorialspoint.com/sql/sql-sub-queries.htm: 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. The GROUP BY command can be used to perform the same function as the ORDER BY in a subquery.

  • Subqueries that return more than one row can only be used with multiple value operators such as the IN operator.

  • The SELECT list cannot include any references to values that evaluate to a BLOB, ARRAY, CLOB, or NCLOB.

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