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What is Oracle UNION ?

• The Oracle UNION operator is used to combine the result sets of 2 or more Oracle SELECT statements.
• It removes duplicate rows between the various SELECT statements.

Syntax:

SELECT expression1, expression2, ... expression_n
FROM tables
[WHERE conditions]
UNION
SELECT expression1, expression2, ... expression_n
FROM tables
[WHERE conditions];

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• Note : Each SELECT statement within the UNION operator must have the same number of fields in the result sets with similar data types.

Oracle Union Query

Sample Database:

• We have a table called wikitechy_employee with four fields (id, name, position, and city). It contains the following data:

• We have another table called orders with three fields (id, customer_name, and orderid).

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Example:

SELECT City FROM wikitechy_employee
UNION
SELECT City FROM orders
ORDER BY City;

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Note:

• There must be same number of expressions in both SELECT statements.

Union:

1. Select statement is used to select city column from the wikitechy_employee table and similarly city column from orders table.
2. Union Keyword is used to combines distinct values in city column from both tables.
3. If several employee and customers share same city, each city will only be selected.

• Note: Use Union All keyword instead of union to select all the duplicate values.

Union UnionAll Except Intersect

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