Rewrite sub-queries to semi-join.

Sure, I can help you with that!

To rewrite sub-queries to semi-join, you can use the EXISTS keyword in the WHERE clause of the outer query. The EXISTS keyword is used to test for the existence of any record in a subquery and returns a boolean value.

Here's an example of rewriting a sub-query to a semi-join:

Original sub-query:

SELECT *
FROM table1
WHERE column1 IN (SELECT column1 FROM table2);

Semi-join version:

SELECT *
FROM table1
WHERE EXISTS (SELECT 1 FROM table2 WHERE table1.column1 = table2.column1);

In the semi-join version, the sub-query is replaced with the EXISTS keyword and the necessary conditions are added to link the sub-query to the outer query. This can improve the performance of the query by reducing the number of records that need to be processed.

I hope this answers your question! Let me know if you have any more.