This blog post is inspired from my earlier blog post of UPDATE From SELECT Statement – Using JOIN in UPDATE Statement – Multiple Tables in Update Statement. In the blog post I discussed about how we can use JOIN and multiple tables in the UPDATE statement. There were plenty of the emails after this blog post discussing about using JOIN in the DELETE statement as well using multiple tables in the DELETE statement.
It is totally possible to use JOIN and multiple tables in the DELETE statement. Let us use the same table structure which we had used previously.
Let us see the following example. We have two tables Table 1 and Table 2.
-- Create table1
CREATE TABLE Table1 (Col1 INT, Col2 INT, Col3 VARCHAR(100))
INSERT INTO Table1 (Col1, Col2, Col3)
SELECT 1, 11, 'First'
SELECT 11, 12, 'Second'
SELECT 21, 13, 'Third'
SELECT 31, 14, 'Fourth'
-- Create table2
CREATE TABLE Table2 (Col1 INT, Col2 INT, Col3 VARCHAR(100))
INSERT INTO Table2 (Col1, Col2, Col3)
SELECT 1, 21, 'Two-One'
SELECT 11, 22, 'Two-Two'
SELECT 21, 23, 'Two-Three'
SELECT 31, 24, 'Two-Four'
Now let us check the content in the table.
Now pay attention to following diagram. Here we have two tables Table1 and Table 2. Our requirement is that we want to delete those two records from Table1 where Table2 Col3 values are “Two-Three” and “Two-Four” and Col1 in both the tables are the same.
I have explained the above statement very easily in following diagram.
When you look at this it looks very simple but when we try to think the solution, I have seen developers coming up with many different solutions for example sometime they write cursor, table variables, local variables etc. However, the easiest and the most clean way is to use JOIN clause in the DELETE statement and use multiple tables in the DELETE statement and do the task.
-- Delete data from Table1
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.Col1 = t2.Col1
WHERE t2.Col3 IN ('Two-Three','Two-Four')
Now let us select the data from these tables.
-- Check the content of the table
As you can see that using JOIN clause in DELETE statement it makes it very easy to update data in one table from another table. You can additionally use MERGE statement to do the same as well, however I personally prefer this method. Let us clean up the clause by dropping the tables which we have created.
DROP TABLE Table1
DROP TABLE Table2
Do let me know if you use any other trick in similar situations. If you do, I would like to learn more about it.
Reference: Pinal Dave (http://blog.sqlauthority.com)