Set Operators

Set operators combine the results of two component queries into a single result. Queries containing set operators are called compound queries. Table 3-9 lists SQL set operators.

Table 3-9 Set Operators

Operator	Returns
UNION	All rows selected by either query.
UNION ALL	All rows selected by either query, including all duplicates.
INTERSECT	All distinct rows selected by both queries.
MINUS	All distinct rows selected by the first query but not the second.

All set operators have equal precedence. If a SQL statement contains multiple set operators, Oracle evaluates them from the left to right if no parentheses explicitly specify another order.

The corresponding expressions in the select lists of the component queries of a compound query must match in number and datatype. If component queries select character data, the datatype of the return values are determined as follows:

• If both queries select values of datatype CHAR, the returned values have datatype CHAR.

• If either or both of the queries select values of datatype VARCHAR2, the returned values have datatype VARCHAR2.

Examples

Consider these two queries and their results:

SELECT part
    FROM orders_list1;

PART 
---------- 
SPARKPLUG 
FUEL PUMP 
FUEL PUMP 
TAILPIPE 

SELECT part 
    FROM orders_list2;

PART 
---------- 
CRANKSHAFT 
TAILPIPE 
TAILPIPE 

The following examples combine the two query results with each of the set operators.

UNION Example

The following statement combines the results with the UNION operator, which eliminates duplicate selected rows. This statement shows how datatype must match when columns do not exist in one or the other table:

SELECT part, partnum, to_date(null) date_in
    FROM orders_list1
UNION
SELECT part, to_date(null), date_in
    FROM orders_list2;

PART       PARTNUM DATE_IN
---------- ------- -------- 
SPARKPLUG  3323165 
SPARKPLUG          10/24/98
FUEL PUMP  3323162
FUEL PUMP          12/24/99
TAILPIPE   1332999
TAILPIPE           01/01/01
CRANKSHAFT 9394991
CRANKSHAFT         09/12/02

SELECT part 
    FROM orders_list1 
UNION 
SELECT part 
    FROM orders_list2;

PART 
---------- 
SPARKPLUG 
FUEL PUMP 
TAILPIPE 
CRANKSHAFT 

UNION ALL Example

The following statement combines the results with the UNION ALL operator, which does not eliminate duplicate selected rows:

SELECT part 
    FROM orders_list1 
UNION ALL 
SELECT part 
    FROM orders_list2;

PART 
---------- 
SPARKPLUG 
FUEL PUMP 
FUEL PUMP 
TAILPIPE 
CRANKSHAFT 
TAILPIPE 
TAILPIPE 

Note that the UNION operator returns only distinct rows that appear in either result, while the UNION ALL operator returns all rows. A PART value that appears multiple times in either or both queries (such as 'FUEL PUMP') is returned only once by the UNION operator, but multiple times by the UNION ALL operator.

INTERSECT Example

The following statement combines the results with the INTERSECT operator, which returns only those rows returned by both queries:

SELECT part 
    FROM orders_list1 
INTERSECT 
SELECT part 
    FROM orders_list2;

PART 
---------- 
TAILPIPE 

MINUS Example

The following statement combines results with the MINUS operator, which returns only rows returned by the first query but not by the second:

SELECT part 
    FROM orders_list1 
MINUS 
SELECT part 
    FROM orders_list2;

PART 
---------- 
SPARKPLUG 
FUEL PUMP