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Oracle® Database SQL Language Reference
11g Release 1 (11.1)

B28286-07
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The UNION [ALL], INTERSECT, MINUS Operators

You can combine multiple queries using the set operators UNION, UNION ALL, INTERSECT, and MINUS. All set operators have equal precedence. If a SQL statement contains multiple set operators, then Oracle Database evaluates them from the left to right unless 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 must be in the same datatype group (such as numeric or character).

If component queries select character data, then the datatype of the return values are determined as follows:

If component queries select numeric data, then the datatype of the return values is determined by numeric precedence:

In queries using set operators, Oracle does not perform implicit conversion across datatype groups. Therefore, if the corresponding expressions of component queries resolve to both character data and numeric data, Oracle returns an error.

See Also:

Table 2-10, "Implicit Type Conversion Matrix" for more information on implicit conversion and "Numeric Precedence" for information on numeric precedence

Examples The following query is valid:

SELECT 3 FROM DUAL
   INTERSECT
SELECT 3f FROM DUAL;

This is implicitly converted to the following compound query:

SELECT TO_BINARY_FLOAT(3) FROM DUAL
   INTERSECT
SELECT 3f FROM DUAL;

The following query returns an error:

SELECT '3' FROM DUAL
   INTERSECT
SELECT 3f FROM DUAL;

Restrictions on the Set Operators The set operators are subject to the following restrictions:

Note:

To comply with emerging SQL standards, a future release of Oracle will give the INTERSECT operator greater precedence than the other set operators. Therefore, you should use parentheses to specify order of evaluation in queries that use the INTERSECT operator with other set operators.

UNION Example The following statement combines the results of two queries with the UNION operator, which eliminates duplicate selected rows. This statement shows that you must match datatype (using the TO_CHAR function) when columns do not exist in one or the other table:

SELECT location_id, department_name "Department", 
   TO_CHAR(NULL) "Warehouse"  FROM departments
   UNION
   SELECT location_id, TO_CHAR(NULL) "Department", warehouse_name 
   FROM warehouses;

LOCATION_ID Department                     Warehouse
----------- ------------------------------ ---------------------------
       1400 IT
       1400                                Southlake, Texas
       1500 Shipping
       1500                                San Francisco
       1600                                New Jersey
       1700 Accounting
       1700 Administration
       1700 Benefits
       1700 Construction
       1700 Contracting
       1700 Control And Credit
...

UNION ALL Example The UNION operator returns only distinct rows that appear in either result, while the UNION ALL operator returns all rows. The UNION ALL operator does not eliminate duplicate selected rows:

SELECT product_id FROM order_items
UNION
SELECT product_id FROM inventories
ORDER BY product_id;

SELECT location_id  FROM locations 
UNION ALL 
SELECT location_id  FROM departments
ORDER BY location_id;

A location_id value that appears multiple times in either or both queries (such as '1700') 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 unique rows returned by both queries:

SELECT product_id FROM inventories
INTERSECT
SELECT product_id FROM order_items
ORDER BY product_id;

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

SELECT product_id FROM inventories
MINUS
SELECT product_id FROM order_items
ORDER BY product_id;