Question about JOINs and table order

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Question about JOINs and table order

Author

Topic

Xercister
Starting Member

6 Posts

Posted - 2013-03-19 : 22:08:58

So I've been reading up on JOINS and for the most part I get it. However I do have a few questions that I am not finding answers to.

1. If you have 3 tables in your database.

Table 1, Table 2, Table 3

Table 1 relates to Table 2
Table 1 relates to Table 3
Table 2 does not relate to Table 3

If you wanted to use these tables together can you do something like this?

SELECT *
FROM Table 1 AS T1
JOIN Table 2 AS T2 ON T1.xx = T2.xx
JOIN TABLE 3 AS T3 ON T1.xx = T2.xx

If not, why not?

2. Order of the ON clause in the JOIN syntax.

If you're joining Table 1 and Table 2 I would assume you would use this.

FROM Table 1 AS T1
JOIN Table 2 AS T2 ON T2.xx = T1.xx.

Does it matter what order the fields are that you're joining them on?

Is that the same as this?

FROM Table 1 AS T1
JOIN Table 2 AS T2 ON T1.xx = T2.xx

Thanks for the help in advance!

chadmat
The Chadinator

1974 Posts

Posted - 2013-03-20 : 00:29:31

1. Yes
2. Yes you can, order doesn't matter.

-Chad

UnemployedInOz
Yak Posting Veteran

54 Posts

Posted - 2013-03-21 : 01:59:59

This doesnt look right
SELECT *
FROM Table 1 AS T1
JOIN Table 2 AS T2 ON T1.xx = T2.xx
JOIN TABLE 3 AS T3 ON T1.xx = T2.xx

It should be

SELECT *
FROM Table 1 AS T1
JOIN Table 2 AS T2 ON T1.xx = T2.xx
JOIN TABLE 3 AS T3 ON T1.xx = T3.xx -- Should be T3.xx not T2.xx

chadmat
The Chadinator

1974 Posts

Posted - 2013-03-21 : 02:10:55

quote:
Originally posted by UnemployedInOz

This doesnt look right
SELECT *
FROM Table 1 AS T1
JOIN Table 2 AS T2 ON T1.xx = T2.xx
JOIN TABLE 3 AS T3 ON T1.xx = T2.xx

It should be

SELECT *
FROM Table 1 AS T1
JOIN Table 2 AS T2 ON T1.xx = T2.xx
JOIN TABLE 3 AS T3 ON T1.xx = T3.xx -- Should be T3.xx not T2.xx

Yes, you are correct, I missed that.

-Chad

Xercister
Starting Member

6 Posts

Posted - 2013-03-21 : 07:37:56

quote:
Originally posted by UnemployedInOz

This doesnt look right
SELECT *
FROM Table 1 AS T1
JOIN Table 2 AS T2 ON T1.xx = T2.xx
JOIN TABLE 3 AS T3 ON T1.xx = T2.xx

It should be

SELECT *
FROM Table 1 AS T1
JOIN Table 2 AS T2 ON T1.xx = T2.xx
JOIN TABLE 3 AS T3 ON T1.xx = T3.xx -- Should be T3.xx not T2.xx

Ah yea, gotta love those typos.. Thanks for catching that.

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