Gbase8sunion all operator

If you use UNION ALL Operator , Then all qualified rows are returned from the two queries , Without excluding any repetition

That's ok .（ If you use UNION Operator without ALL Keyword to combine two queries , From the combination of qualified rows

Remove any duplicate rows from the set of . in other words , If there are many lines , Each column contains exactly the same value , So just keep

a line .）

The next example uses UNION ALL To combine two SELECT Result of statement , Without removing duplicate lines . The query returns in 2007

In the first quarter of 2008 List of all calls received during the first quarter of the year .

SELECT customer_num, call_code FROM cust_calls

WHERE call_dtime BETWEEN

DATETIME (2007-1-1) YEAR TO DAY

AND DATETIME (2007-3-31) YEAR TO DAY

UNION ALL

SELECT customer_num, call_code FROM cust_calls

WHERE call_dtime BETWEEN

DATETIME (2008-1-1)YEAR TO DAY

AND DATETIME (2008-3-31) YEAR TO DAY;

If you want to remove duplicate rows from the result set , Please use without keywords ALL Of UNION As a set operator between queries .

In the previous example , If two SELECT Statements all return combinations 101 B, be UNION Operator will cause the combination

List only once .（ If you want to remove each SELECT Repeated lines in the statement , Then please follow Projection Clause

Select Use before the list DISTINCT or UNIQUE keyword , Like Allow repetition As described in .）

For designation, only UNION Set operation of operator ,ALL Keywords are valid . If ALL Keep up with the

INTERSECT、MINUS or EXCEPT After the set operator , These set operators exclude duplicate parts , Then database

The server sent an error .

To get information about how the database server has NLCASE INSENSITIVE Duplicate identification in the database of attribute NCHAR

or NVARCHAR Value information , See topic In case sensitive databases NCHAR and NVARCHAR surface

Da da .