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UNION ALL



Oracle - Union All


In Oracle, the UNION ALL operator is used to combine the result sets of 2 or more SELECT statements. It is different from UNION operator in a way that it does not remove duplicate rows between the various SELECT statements. It returns all of the rows.

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


Difference between UNION and UNION ALL operators :


In very simple words the difference between UNION and UNION ALL is that UNION will omit duplicate records whereas UNION ALL will include duplicate records.


Syntax :
SELECT expression1, expression2, ... expression_n  
FROM table1  
WHERE conditions  
UNION ALL  
SELECT expression1, expression2, ... expression_n  
FROM table2  
WHERE conditions;   

Parameters :


  • expression1, expression2, expression_n: It specifies the columns that you want to retrieve. Number of expressions must be same in both SELECT statements.

  • table1, table2: It specifies the table name that you want to retrieve records from.

  • conditions: It specifies the conditions that must be fulfilled for the records to be selected.


    Oracle UNION ALL Operator Example :


    SELECT supplier_id  
    FROM suppliers  
    UNION ALL  
    SELECT supplier_id  
    FROM order_details;  
    

    The above example will return the supplier_id multiple times in the result set if the same value appeared in both the supplier_id and order_details table.


    Output :

    Supplier_ID
    1
    2
    3
    50
    50
    21
    22
    25
    28
    20


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