Rules that Sub Queries must follow

Rules that Sub Queries must follow

  • 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 cannot be used in a subquery, although the main query can use an ORDER BY. The GROUP BY 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.
  • A subquery cannot be immediately enclosed in a set function.
  • The BETWEEN operator cannot be used with a subquery; however, the BETWEEN operator can be used within the subquery.

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