Statement Set Operators¶

UNION, DIFFERENCE, INTERSECTION¶

Statement set operators are used to get union, difference or intersection on the result of more than one query statement specified as an operand. Note that the data types of the data to be retrieved from the target tables of the two query statements must be identical or implicitly castable.

query_term statement_set_operator [qualifier] <query_term>
[{statement_set_operator [qualifier] <query_term>}];

    <query_term> ::=
        query_specification
        subquery

qualifier
- DISTINCT, DISTINCTROW or UNIQUE(A returned instance is a distinct value.)
- ALL (All instances are returned. Duplicates are allowed.)
statement_set_operator
- UNION (union)
- DIFFERENCE (difference)
- INTERSECT | INTERSECTION (intersection)

The following table shows statement set operators supported by CUBRID.

Statement Set Operators

Statement Set Operator	Description	Note
UNION	Union Duplicates are not allowed.	Outputs all instance results containing duplicates with UNION ALL
DIFFERENCE	Difference Duplicates are not allowed.	Same as the EXCEPT operator. Outputs all instance results containing duplicates with DIFFERENCE ALL.
INTERSECTION	Intersection Duplicates are not allowed.	Same as the INTERSECTION operator. Outputs all instance results containing duplicates with INTERSECTION ALL.

The following are the examples which execute queries with statement set operators.

CREATE TABLE nojoin_tbl_1 (ID INT, Name VARCHAR(32));

INSERT INTO nojoin_tbl_1 VALUES (1,'Kim');
INSERT INTO nojoin_tbl_1 VALUES (2,'Moy');
INSERT INTO nojoin_tbl_1 VALUES (3,'Jonas');
INSERT INTO nojoin_tbl_1 VALUES (4,'Smith');
INSERT INTO nojoin_tbl_1 VALUES (5,'Kim');
INSERT INTO nojoin_tbl_1 VALUES (6,'Smith');
INSERT INTO nojoin_tbl_1 VALUES (7,'Brown');

CREATE TABLE nojoin_tbl_2 (id INT, Name VARCHAR(32));

INSERT INTO nojoin_tbl_2 VALUES (5,'Kim');
INSERT INTO nojoin_tbl_2 VALUES (6,'Smith');
INSERT INTO nojoin_tbl_2 VALUES (7,'Brown');
INSERT INTO nojoin_tbl_2 VALUES (8,'Lin');
INSERT INTO nojoin_tbl_2 VALUES (9,'Edwin');
INSERT INTO nojoin_tbl_2 VALUES (10,'Edwin');

--Using UNION to get only distinct rows
SELECT id, name FROM nojoin_tbl_1
UNION
SELECT id, name FROM nojoin_tbl_2;

           id  name
===================================
            1  'Kim'
            2  'Moy'
            3  'Jonas'
            4  'Smith'
            5  'Kim'
            6  'Smith'
            7  'Brown'
            8  'Lin'
            9  'Edwin'
           10  'Edwin'

--Using UNION ALL not eliminating duplicate selected rows
SELECT id, name FROM nojoin_tbl_1
UNION ALL
SELECT id, name FROM nojoin_tbl_2;

           id  name
===================================
            1  'Kim'
            2  'Moy'
            3  'Jonas'
            4  'Smith'
            5  'Kim'
            6  'Smith'
            7  'Brown'
            5  'Kim'
            6  'Smith'
            7  'Brown'
            8  'Lin'
            9  'Edwin'
           10  'Edwin'

--Using DEFFERENCE to get only rows returned by the first query but not by the second
SELECT id, name FROM nojoin_tbl_1
DIFFERENCE
SELECT id, name FROM nojoin_tbl_2;

           id  name
===================================
            1  'Kim'
            2  'Moy'
            3  'Jonas'
            4  'Smith'

--Using INTERSECTION to get only those rows returned by both queries
SELECT id, name FROM nojoin_tbl_1
INTERSECT
SELECT id, name FROM nojoin_tbl_2;

           id  name
===================================
            5  'Kim'
            6  'Smith'
            7  'Brown'