UNION CLAUSE

The union operator in sql is used to combined two different queries into a singel table. For eg:-we have one table which have information about employee, also have another table that have information about their department, and their is no relationship between them. Suppose that both employee and department table have one similar fields that have information about employee_id, and we want to get all information about employee_id from both the tables at the same time. We can do this by using union clause.

The important thing which have to be in mind while using union clause is that.

- All SELECT statement that we use to combine in union query must have same number of columns to be fetched

Syntax of union clause

SELECT column(s)
FROM table
WHERE [condition]
UNION
SELECT column(s)
FROM table
WHERE [condition];

eg;-

Below is a selection from the "Customers" table:

CustomerID       CustomerName             Address              City           PostalCode     
1                     suresh             tilak road            rishikesh      240098 
2                     amit               survey road           bahadurgarh    293400
3                     saurav            neshvilla road         dehardun       248001

And a selection from the "Suppliers" table:

SupplierID        SupplierName       Address           City        PostalCode   
1                 ram                kalidas road     lucknow       289100
2                 shyam              dobhalwala       delhi         200001
3                 radha               cant            agra          230001

The following SQL statement give all the different cities from the "Customers" and the "Suppliers" tables:-

SELECT City FROM Customers
UNION
SELECT City FROM Suppliers
ORDER BY City;

OUTPUT

city
rishikesh
bahadurgarh
dehradun
lucknow
delhi
agra