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On 01-01-16 22:08, Paul Steyn wrote:
Hi Don,

Your SELECT statement is indeed incorrect; it seems as though you don't
fully understand joins (I could be mistaken, but your syntax is off
by enough to suggest this).

Firstly, choose a format for your SELECT statement to make it easier to
read. I've reformatted it below using one such formatting standard that
I've used in the past, but you can of course choose your own. The
important thing is that it isn't simply one large blob of text.

Secondly, use table aliases. After the table name in the FROM clause,
you can include a table alias, which you can use elsewhere (including in
the SELECT clause) to refer to the table. These are often much shorter
than the table names, making the whole statement easier to read. Also,
if you are including a table more than once (for different join
conditions), I think you are required to have aliases to distinguish
between the two table uses. You are actually doing this in your
statement, and it gives rise to an ambiguity.

Thirdly, JOINs are complicated, as there are many options: INNER

The most common (in my experience) are INNER and LEFT OUTER JOINs.
Don't worry about the rest for now.

Think of it this way:

For inner joins, with the condition in the FROM clause

(i.e. FROM tableA a INNER JOIN tableB b on =

You are adding all rows from tableA to a result set, then, for each row
in tableB that matches the condition, you are adding all the fields
from tableB to that row of the result set (if more than one row matches
a row in the result set, the existing row is duplicated). If a row in
the result set doesn't match any rows in tableB, it is removed from the
result set.

For OUTER JOINS, of the form:

FROM tableA a LEFT OUTER JOIN tableB b on =

You are doing the same thing, except that should a row in the result
set not match any rows in tableB, it is not discarded from the result
set, and instead NULL values are used for all fields that would
otherwise have come from tableB.

You are absolutely right, but the *syntax* is different in LO ....
see link i posted earlier

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