Chapter 9 SQL Statements
633
UNION operation
Use this statement to combine the results of two or more select statements.
select-without
-
order-by
… UNION [ALL]
select-without
-
order-by
… [ UNION [ALL]
select-without
-
order-by
] …
… [ ORDER BY
integer
[ ASC | DESC ], … ]
Must have SELECT permission for each of the component SELECT
statements.
None.
"SELECT statement" on page 601
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, Adaptive
Server 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 that are displayed
for the first SELECT statement.
♦
SQL/92 Entry level.
♦
Sybase Supported by Adaptive Server Enterprise, which also supports
a COMPUTE clause.
♦ List all distinct surnames of employees and customers.
SELECT emp_lname
FROM Employee
UNION
SELECT lname
FROM Customer
Function
Syntax
Permissions
Side effects
See also
Description
Standards and
compatibility
Examples
To Next Page
Loading...