Understanding SQL LEFT JOIN with Examples

SQL LEFT JOIN

The LEFT JOIN (also known as LEFT OUTER JOIN) returns all records from the left table and the matching records from the right table. When no match exists, NULL appears in the right table columns.

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Syntax

SELECT Table1.Column1, Table2.Column2
FROM Table1
LEFT JOIN Table2
  ON Table1.CommonColumn = Table2.CommonColumn;

Example 1: Staff & Unit

SELECT s.StaffID, s.Staff_Name, s.Salary, u.UnitID, u.Unit_Name
FROM staff s
LEFT JOIN unit u ON s.StaffID = u.Staff_ID;

Returns every staff member; unmatched staff get NULL for unit columns.

Example 2: Credit & Client

SELECT c.LoanID, c.Branch, c.Amount, cl.ClientID, cl.Client_Name
FROM credit c
LEFT JOIN client cl ON c.LoanID = cl.LoanID;

All loans appear; loans without a client show NULL for client columns.

Example 3: Buyers & Purchases

SELECT b.BuyerID, b.Buyer_Name, p.PurchaseID, p.Amount
FROM buyers b
LEFT JOIN purchases p ON b.BuyerID = p.BuyerID;

LEFT JOIN vs RIGHT JOIN vs INNER JOIN

• INNER JOIN: Only matching rows from both tables.
• LEFT JOIN: All from left + matches from right (NULL where missing).
• RIGHT JOIN: All from right + matches from left.

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Conclusion

LEFT JOIN ensures you keep every row from the left table, even when there is no match on the right. It is perfect for reporting on optional relationships. For more SQL tutorials, keep exploring .

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