SQL UNION GROUP BY

SQL UNION Operator

UNION operator is used to combine the results of two or more SELECT statements

• Every SELECT statement within UNION must have the same number of columns

• The columns must also have similar data types

• The columns in every SELECT statement must also be in the same order

SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2

UNION ALL

The UNION operator selects only distinct values by default. To allow duplicate values, use UNION ALL:

SELECT column_name(s)FROMtable1
UNION ALL
SELECT column_name(s)FROMtable2;

UNION With WHERE

SELECT City, Country FROM Customers
WHERE Country='Germany'
UNION
SELECT City, Country FROM Suppliers
WHERE Country='Germany'
ORDER BY City;

UNION ALL With WHERE === Which gives duplicate values

SELECT City, Country FROM Customers
WHERE Country='Germany'
UNION ALL
SELECT City, Country FROM Suppliers
WHERE Country='Germany'
ORDER BY City;

SQL GROUP BY

The GROUP BY statement groups rows that have the same values into summary rows, like "find the number of customers in each country".

The GROUP BY statement is often used with aggregate functions (COUNT(), MAX(), MIN(), SUM(), AVG()) to group the result-set by one or more columns.

GROUP BY Syntax

SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
ORDER BY column_name(s);