What are the steps followed by sql engine to execute the query..??

sql inner-join internal
henry picture henry · May 8, 2009 · Viewed 7.7k times · Source

My question is not how to use inner join in sql. I know about how it matches between table a and table b.

I'd like to ask how is the internal working of inner working. What algorithm it involves? What happens internally when joining multiple tables?

Answer

Lucero picture Lucero · May 8, 2009

There are different algorithms, depending on the DB server, indexes and data order (clustered PK), whether calculated values are joined or not etc.

Have a look at a query plan, which most SQL systems can create for a query, it should give you an idea what it does.

Related questions

What is the difference between "INNER JOIN" and "OUTER JOIN"?

Also how do LEFT JOIN, RIGHT JOIN and FULL JOIN fit in?

Read More
What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN?

What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN in MySQL?

Read More
How to Delete using INNER JOIN with SQL Server?

I want to delete using INNER JOIN in SQL Server 2008. But I get this error: Msg 156, Level 15, State 1, Line 15 Incorrect syntax near the keyword 'INNER'. My code: DELETE FROM WorkRecord2 INNER JOIN Employee ON EmployeeRun=EmployeeNo WHERE Company = '1' …

Read More