Re: my first use of lateral

On 14 Dec 2012 13:02, Steve Richter wrote:

someone posted about sql lateral recently, which I had never heard
of. Here is my first use of it.

There are 2 files. A header and a detail. Header contains the BOL
number. The detail contains the ship date of all the lines of that
BOL. ( go figure )

Here is the sql that shows the BOL and its ship date:

select a.w1BOL, b.w2sdte
from w1mast a
, lateral ( select c.w2sdte
from w2mast c
where a.w1wacd = c.w2wacd and a.w1sid = c.w2sid
and c.w2sdte<> 0
fetch first row only ) b
where a.w1wacd = 'LAE' and a.w1BOL<> ''

I figure without lateral I have to do a join with group by and
MIN(w2sdte) to eliminate the multiple detail rows. But with lateral I
can use "fetch first row only" which is clearer to read since it does
exactly what I want to be done.

I suspect the LATERAL specification is moot for the given SQL. I expect that the /same/ SQL, but without the LATERAL keyword, will function just fine; no errors, and the identical output\effect. It is the NTE which allows the FETCH FIRST 1 ROW ONLY, not the use of LATERAL.

The Nested Table Expression (NTE) [aka Derived Table] has often been shown in examples on this list. The LATERAL in the syntax diagram is optional [mostly]; i.e. nothing in the above example would seem to imply any requirement for its specification. If there is a reference to the correlation identifier A in the column\expression-list of the SELECT in the NTE, then in my understanding and experience, the LATERAL keyword would be required.