Обсуждение: DESIGN OF A SELECT QUERY
I have designed a SELECT query by hand and by using a query designer and I see a difference. Such a query includes 11 tables and I would like your comments.
The designer result is somthing like:
SELECT fld1, fld2,...,fldn FROM tbl1
INNER JOIN .......
INNER JOIN .......
The query I wrote is as follows although I do not know if it works:
SELECT fld1, fld2,...,fldn FROM
tbl1
INNER JOIN...ON....
INNER JOIN...ON....,
tlb2
INNER JOIN...ON...
INNER JOIN...ON...,
tbl3
INNER JOIN...ON...
INNER JOIN...ON...
If you watch closely, the query generated by the designer includes only one table in the FROM and all of the INNER JOIN's follow after it.
My design includes several tables in the FROM each one with its own INNER JOIN's.
Is this valid?
Please advice.
Respectfully,
Jorge Maldonado
JORGE MALDONADO wrote: > I have designed a SELECT query by hand and by using a query designer and > I see a difference. Such a query includes 11 tables and I would like > your comments. > > The designer result is somthing like: > SELECT fld1, fld2,...,fldn FROM tbl1 > INNER JOIN ....... > INNER JOIN ....... > > The query I wrote is as follows although I do not know if it works: > SELECT fld1, fld2,...,fldn FROM > tbl1 > INNER JOIN...ON.... > INNER JOIN...ON...., > > tlb2 > INNER JOIN...ON... > INNER JOIN...ON..., > > tbl3 > INNER JOIN...ON... > INNER JOIN...ON... > > If you watch closely, the query generated by the designer includes only > one table in the FROM and all of the INNER JOIN's follow after it. > My design includes several tables in the FROM each one with its own > INNER JOIN's. > > Is this valid? > Please advice. It may be valid, but the semantics will differ between the two forms. The "designer result" will create one massive INNER JOIN between however many tables. The second form will create a cross join between the different INNER JOIN parts. -- Lew