User's Guide

Part VI. SQL Anywhere Reference

Chapter 43. Watcom-SQL Statements

Function

To combine the results of two or more select statements.

Syntax

     select-without-order-by
          ... UNION [ALL] select-without-order-by
          ... [ UNION [ALL] select-without-order-by ] ...
          ... [ ORDER BY integer [ ASC | DESC ], ... ]

Usage

Anywhere.

Permissions

Must have SELECT permission for each of the component SELECT statements.

Side effects

None.

See also

• SELECT statement

Description

The results of several SELECT statements can be combined into a larger result using UNION. The component SELECT statements must each have the same number of items in the select list, and cannot contain an ORDER BY clause.

The results of UNION ALL are the combined results of the component SELECT statements. The results of UNION are the same as UNION ALL except that duplicate rows are eliminated. Eliminating duplicates requires extra processing, so UNION ALL should be used instead of UNION where possible.

If corresponding items in two select lists have different data types, SQL Anywhere will choose a data type for the corresponding column in the result and automatically convert the columns in each component SELECT statement appropriately.

If ORDER BY is used, only integers are allowed in the order by list. These integers specify the position of the columns to be sorted.

The column names displayed are the same column names which would be displayed for the first SELECT statement.

Examples

List all distinct surnames of employees and customers.

     SELECT emp_lname
     FROM Employee
     UNION
     SELECT lname
     FROM Customer ;