PostgreSQL Left Join

All the matched and unmatched records are retrieved from the table present on the left hand side of the join operator.Left Join is used to return all data or records from the Table 1 plus match records to tables 2. If there is no match, the result from the right will be NULL. This is also known as LEFT (OUTER) JOIN.

Left Joins Syntax :

The syntax of the Left Joins statement is −

SELECT col_name,...
FROM table_name1 t1  [LEFT] JOIN table_name2 t2
ON t1.col_name = t2.col_name



PostgreSQL Left Join Example :

Consider the Customer table with the following records -

ID Name Age Address Salary
1 Aarav 36 Udaipur 35000
2 Vivaan 33 Mumbai 30000
3 Reyansh 28 Chennai 40000
4 Muhammad 29 Udaipur 50000
5 Sai 27 Mumbai 27000


Consider the Order table with the following records -

OID Date CustomerID Amount
102 2019-10-08 00:00:00 3 3000
100 2019-10-08 00:00:00 3 1500
101 2019-11-20 00:00:00 2 1800
103 2018-05-20 00:00:00 4 2500


TEST CASE 1 :-Let us join these two tables using the Left JOIN as follows

SELECT  ID, Name, Amount, Date
FROM Customer
LEFT JOIN Order
ON Customer.ID = Order.CustomerID;


The result for the respective PostgreSQL query is as follows −

ID Name Amount Date
1 Aarav NULL NULL
2 Vivaan 1800 2019-11-20 00:00:00
3 Reyansh 3000 2019-10-08 00:00:00
3 Reyansh 1500 2019-10-08 00:00:00
4 Muhammad 2500 2018-05-20 00:00:00
5 Sai NULL NULL




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