Name
UNION
Synopsis
SELECT . . . UNION [ALL|DISTINCT] [SELECT . . . ]
The UNION
keyword
unites the results of multiple SELECT
statements
into one results set. The SELECT
statements can
retrieve data from the same table or from different tables. If
different tables are used, the results set generated by each SQL
statement should match in column count and in the order of column
types. The column names do not need to be the same, but the data sent
to the respective fields in the results set needs to match. Here is
an example of a UNION
used to merge the results of
two SELECT
statements:
SELECT CONCAT(name_first, SPACE(1), name_last) AS Name, telephone_work AS Telephone FROM employees UNION SELECT location, telephone FROM branches ORDER BY Name;
This statement will present a list
of employees and branch office locations in one column, with the
telephone number for each in the second. The column headings used for
the results set will be the ones used for the first
SELECT
statement. Because of the ORDER
BY
clause, the results will be sorted by the values for the
alias Name. Otherwise, the names of employees
would be listed before the names of offices.
The example shown merges the results of only two
SELECT
statements. You can merge several
SELECT
statements, entering the
UNION
keyword between each one.
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