Have to run a Cross Join in SQL where a value is NULL?

Question

I have to compare results using two different SQL commands. One with a join statement and one without. I got the command without the join statement to work:

SELECT ord.ORDER#, cust.LASTNAME, cust.FIRSTNAME
FROM ORDERS ord, CUSTOMERS cust
WHERE ord.SHIPDATE IS NULL
AND ord.CUSTOMER# = cust.CUSTOMER#
ORDER BY ord.ORDERDATE;

but can't get the command WITH a join statement to work. Help, please?

Answer 1

I agree with Thread7's answer. You won't need LEFT JOIN though, just JOIN.



LEFT JOIN is a left outer join, and by default JOIN is a cross (or inner) join.



Thread7, if you see this, I refer to this diagram all the time: http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html



Remember that by default, MySQL JOIN is an inner (or cross) join, LEFT JOIN is also called LEFT OUTER JOIN (and same for RIGHT JOINs).

Answer 2

I'm not a SQL expert but this is how I would write it:

SELECT ord.ORDER#, cust.LASTNAME, cust.FIRSTNAME

FROM ORDERS ord LEFT JOIN CUSTOMERS cust ON ord.CUSTOMER# = cust.CUSTOMER#

WHERE ord.SHIPDATE IS NULL

AND ord.CUSTOMER# = cust.CUSTOMER#

ORDER BY ord.ORDERDATE;



Maybe it shouldn't be a LEFT join, but INNER JOIN or RIGHT JOIN. I'm not 100% sure in your case.

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