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In some databases, such as Postgre SQL, when a FROM clause is present, what essentially happens is that the target table is joined to the tables mentioned in the fromlist, and each output row of the join represents an update operation for the target table.

-- the join clause is whatever suits you DECLARE @tbl1 TABLE (id INT, col1 VARCHAR(10), col2 VARCHAR(10)) DECLARE @tbl2 TABLE (id INT, col1 VARCHAR(10), col2 VARCHAR(10)) INSERT @tbl1 SELECT 1, 'a', 'b' UNION SELECT 2, 'b', 'c' INSERT @tbl2 SELECT 1, '1', '2' UNION SELECT 2, '3', '4' UPDATE t SET t.col1 = a.col1 ,t.col2 = a.col2 FROM ( SELECT id, col1, col2 FROM @tbl2) a INNER JOIN @tbl1 t ON = SELECT * FROM @tbl1 SELECT * FROM @tbl2 -- Sample data: --------------------------------------------------------------------------- CREATE TABLE #SOURCE ([ID] INT, [Desc] VARCHAR(10)); CREATE TABLE #DESTINATION ([ID] INT, [Desc] VARCHAR(10)) INSERT INTO #SOURCE VALUES(1,'Desc_1'), (2, 'Desc_2'), (3, 'Desc_3'); INSERT INTO #DESTINATION VALUES(1,'Desc_4'), (2, 'Desc_5'), (3, 'Desc_6'); --------------------------------------------------------------------------- UPDATE #DESTINATION SET #DESTINATION.[Desc] = #SOURCE.[Desc] FROM #SOURCE WHERE #DESTINATION.[ID] = #SOURCE.[ID] AND #Source.[Desc] = 'Desc_2' drop table uno drop table dos create table uno ( uid int, col1 char(1), col2 char(2) ) create table dos ( did int, col1 char(1), col2 char(2), [sql] char(4) ) insert into uno(uid) values (1) insert into uno(uid) values (2) insert into dos values (1,'a','b',null) insert into dos values (2,'c','d','cool') select * from uno select * from dos What I usually do is putting everything in a rollbacked transaction and using the "OUTPUT": in this way I see everything that is about to happen.

When I am happy with what I see, i change the ROLLBACK into COMMIT.

The two hyphens in front of a line indicate that the line is a comment and the text will be ignored by the compiler.

In this case, the comment describes a permissible variation of the syntax.

Specifies the temporary named result set or view, also known as common table expression (CTE), defined within the scope of the UPDATE statement.

The CTE result set is derived from a simple query and is referenced by UPDATE statement.

You will be given questions that you need to solve.

After each exercise, we provide the solution so you can check your answer.

UPDATE summary_data SET current_category = (SELECT category_id FROM products WHERE products.product_id = summary_data.product_id) WHERE EXISTS (SELECT category_id FROM products WHERE products.product_id = summary_data.product_id); If you want to test your skills using the SQL UPDATE statement, try some of our practice exercises.

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