UNION Operation
Creates a union query, which combines the results of two or more independent queries or tables.
Syntax
[TABLE] query1 UNION [ALL] [TABLE] query2 [UNION [ALL] [TABLE] queryn [ ... ]]
The UNION operation has these parts:
| Part | Description |
|---|---|
| query1-n | A SELECT statement, the name of a stored query, or the name of a stored table preceded by the TABLE keyword. |
Remarks
You can merge the results of two or more queries, tables, and SELECT statements, in any combination, in a single UNION operation. The following example merges an existing table named New Accounts and a SELECT statement:
TABLE [New Accounts] UNION ALL
SELECT *
FROM Customers
WHERE OrderAmount > 1000;
By default, no duplicate records are returned when you use a UNION operation; however, you can include the ALL predicate to ensure that all records are returned. This also makes the query run faster.
All queries in a UNION operation must request the same number of fields; however, the fields do not have to be of the same size or data type.
Use aliases only in the first SELECT statement because they are ignored in any others. In the ORDER BY clause, refer to fields by what they are called in the first SELECT statement.
Notes
- You can use a GROUP BY or HAVING clause in each query argument to group the returned data.
- You can use an ORDER BY clause at the end of the last query argument to display the returned data in a specified order.