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VFP 9: Major SQL SELECT Enhancements

Visual FoxPro 9 includes several SQL improvements especially on the SELECT side of things. It's got neat features that already were available in SQL Server like CAST and VarChar data types but some of the fun are on the limitations that have been removed.
In VFP 8 and earlier, you could only do 9 joins in a SELECT statement and only with a maximum of 30 tables. With VFP 9, you're unlimited.
You can reference more than 30 tables or aliases in a single SELECT statement and join them as much as you want.
Smaller applications may not need this but as you come across more and more normalized databases, removing this limitation is huge.
But what's more is the other limitations that have been removed from the SQL - SELECT statement.
- unlimited UNION statements
- you can specify more than 24 items in an IN statement. SELECT * FROM customers where state in ("NC","AL",etc, etc). In previous versions, you had a maximum of 24. Even though this approach would call out for a better criteria, if you are allowing your users to build complex queries, this removes a lot of "why can't I? " type questions.
Perhaps even cooler is how VFP 9 really supports subqueries. Consider the following statement:
SELECT ordid from (select * from ordhist) as x

In previous versions, you might have to do :

SELECT * from ORDHIST where <condition> into cursor x

SELECT ordid from x

Now you can put it all into a single line.

You can also use subqueries as a line item:

SELECT custname,custno, (SELECT sum(totchgs) From frmast) as ntotal,sum(totchgs),sum(totchgs)/(SELECT sum(totchgs) From frmast)*100 as nperc From frmast GROUP BY 1,2

This query shows the customer name, the total of all invoices (in the file), the total invoices for that customer and then the percentage of total invoices that the customer held all in one query.

In earlier versions, this would be done with multiple lines but now you can do it all in one.

All of these changes are going to be a great reason to refactor your older code. One of the joys I always get is trying to reduce the size of my application. With the new SQL enhancements in Europa, it's going to be lots of fun!


Frank Camp said…
The next limitation (at least in the VFP9 Public Beta) that comes to the surface (because we can create more complex SQL statements right now) is the maximum length of one VFP command.

The maximum length is still 8192 characters. When you have to reference many fields (or statements with the IN clause) you can get over this limit.
(Yes, I do have SQL statements that work in SQL 2000 but cannot work in VFP because of this)

So I hope that the Foxteam stretches (or removes) this limitation before the RTM is reached.

Just my 2 cents.
Garrett said…
One very good reason for removing the limit on the IN clause is that GIS software may do queries using this syntax, which used to make it difficult to use Fox with them. I was very happy to see this change....

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