![]() The following query returns the products that do not appear in any sales order: SELECT It is possible to use the WHERE clause to limit the result set. ![]() Order_id Code language: SQL (Structured Query Language) ( sql )Īs you see clearly from the result set, a list of NULL in the order_id column indicates that the corresponding products have not been sold to any customer yet. LEFT JOIN sales.order_items o ON o.product_id = p.product_id The following statement uses the LEFT JOIN clause to query data from the products and order_items tables: SELECT The link between the order_items and the products tables is the product_id column. See the following products and order_items tables:Įach sales order item includes one product. Rows 2 and 3 from the T1 table match rows A and B from the T2 table, respectively. In this illustration, no row from the T2 table matches row 1 from the T1 table therefore, NULL is used. The LEFT JOIN will match rows from the T1 table with the rows from the T2 table using patterns: The following illustrates the LEFT JOIN of two tables T1(1, 2, 3) and T2(A, B, C). In short, the LEFT JOIN clause returns all rows from the left table (T1) and matching rows or NULL values from the right table (T2). If a row from the left table (T1) does not have any matching row from the T2 table, the query combines column values of the row from the left table with NULL for each column value from the right table. If a pair of rows causes the join predicate to evaluate to TRUE, the column values from these rows will be combined to form a new row which is then included in the result set. In this syntax, T1 and T2 are the left and right tables, respectively.įor each row from the T1 table, the query compares it with all the rows from the T2 table. ![]() The following illustrates how to join two tables T1 and T2 using the LEFT JOIN clause: SELECTĬode language: SQL (Structured Query Language) ( sql ) If no matching rows are found in the right table, NULL are used. The LEFT JOIN returns all rows from the left table and the matching rows from the right table. The LEFT JOIN clause allows you to query data from multiple tables. The LEFT JOIN is a clause of the SELECT statement. Introduction to SQL Server LEFT JOIN clause Summary: in this tutorial, you will learn about the SQL Server LEFT JOIN clause and how to query data from multiple tables.
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