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SQL Anywhere 11.0.1 (Français) » SQL Anywhere Server - SQL Reference » Using SQL » SQL statements » SQL statements (P-Z)

 

UNION clause

Use this statement to combine the results of two or more select statements.

Syntax
[ WITH temporary-views ] query-block
  UNION [ ALL | DISTINCT ] query-block
[ ORDER BY [ integer | select-list-expression-name ] [ ASC | DESC ], ... ]
[ FOR XML xml-mode ]
[ OPTION( query-hint, ... ) ]

query-block : see Common elements in SQL syntax

query-hint :
MATERIALIZED VIEW OPTIMIZATION option-value
| FORCE OPTIMIZATION
| option-name = option-value
option-name : identifier
option-value : hostvar (indicator allowed), string, identifier, or number
Parameters
  • OPTION clause   Use this clause to specify hints for executing the statement. The following hints are supported:

    • MATERIALIZED VIEW OPTIMIZATION option-value
    • FORCE OPTIMIZATION
    • option-name = option-value

    For a description of these options, see the OPTIONS clause of the SELECT statement.

Remarks

The results of several query blocks can be combined into a larger result using UNION. Each query-block must have the same number of items in the select list.

The results of UNION ALL are the combined results of the query blocks. 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. UNION DISTINCT is identical to UNION.

If corresponding items in two select lists have different data types, SQL Anywhere chooses a data type for the corresponding column in the result and automatically convert the columns in each query-block appropriately.

The first query block of the UNION is used to determine the names to be matched with the ORDER BY clause.

The column names displayed are the same column names that are displayed for the first query-block. An alternative way of customizing result set column names is to use the WITH clause on the query-block.

Permissions

Must have SELECT permission for each query-block.

Side effects

None.

See also
Standards and compatibility
  • SQL/2003   Core feature.

Example

List all distinct surnames of employees and customers.

SELECT Surname
FROM Employees
UNION
SELECT Surname
FROM Customers;