Welcome to OStack Knowledge Sharing Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
340 views
in Technique[技术] by (71.8m points)

sql - Does INNER JOIN performance depends on order of tables?

A question suddenly came to my mind while I was tuning one stored procedure. Let me ask it -

I have two tables, table1 and table2. table1 contains huge data and table2 contains less data. Is there performance-wise any difference between these two queries(I am changing order of the tables)?

Query1:

SELECT t1.col1, t2.col2
FROM table1 t1
INNER JOIN table2 t2
ON t1.col1=t2.col2

Query2:

SELECT t1.col1, t2.col2
FROM table2 t2
INNER JOIN table1 t1
ON t1.col1=t2.col2

We are using Microsoft SQL server 2005.

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Answer

0 votes
by (71.8m points)

Aliases, and the order of the tables in the join (assuming it's INNER JOIN) doesn't affect the final outcome and thus doesn't affect performance since the order is replace (if needed) when the query is executed.

You can read some more basic concepts about relational algebra here: http://en.wikipedia.org/wiki/Relational_algebra#Joins_and_join-like_operators


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome to OStack Knowledge Sharing Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...