UNION AND UNION ALL[EXAMPLE]

 Create two tables(CUSTOMERTABLE and CUSTOMERTABLE1)

CUSTOMERTABLE :

CUSTOMERTABLE1 :

UNION:

SELECT CUSTOMERID,name FROM CUSTOMERTABLE

UNION

 

SELECT CUSTOMERID,CUSTOMERNAME from CUSTOMERTABLE1;

 

UNION ALL :

SELECT CUSTOMERID,name FROM CUSTOMERTABLE

UNION all

SELECT CUSTOMERID,CUSTOMERNAME from CUSTOMERTABLE1;

General Error

SELECT CUSTOMERID,name FROM CUSTOMERTABLE

UNION all

SELECT CUSTOMERID,CUSTOMERNAME,NICKNAME from CUSTOMERTABLE1;

output:

ORA-01789: query block has incorrect number of result columns

General Error

SELECT name FROM CUSTOMERTABLE

UNION all

SELECT CUSTOMERID from CUSTOMERTABLE1;

output:

ORA-01790: expression must have same datatype as corresponding expression