Re: SQL(embedded or not) and OPNQRYF

[Carel Teijgeler <teygeler@xxxxxxx>]

Billy Rowe wrote:

> Does SQL and/or OpnQryF filter records before the joining of 2 files?
>
> For example,  If I wanted to join a Customer table to the Transaction table
> only for let's say customer number 222.
>
> Would the system join the file first and then filter the records OR
> would the system filter the records first and then join only the
> corresponding
> customer(222) to it's transactions for presentation to the screen or a
> Program?
>
> TIA,
> Billy

Billy,

To my knowledge, any query using the query engine will first join the file, then
check the selection criteria and lastly, return the selected fields.

So, if your query looks like this:

    SELECT fielda, fieldb FROM file WHERE fielda = 222

then the query engine will
1) do the FROM
2) do the WHERE
3) do the SELECT

This is my understanding of SQL (query) of 6 years ago. I do not think it has
changed since.

Regards,

Carel Teijgeler


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