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Message
From
19/11/2007 14:06:31
 
 
To
16/11/2007 17:38:25
General information
Forum:
Visual FoxPro
Category:
Databases,Tables, Views, Indexing and SQL syntax
Environment versions
Visual FoxPro:
VFP 9
OS:
Windows XP
Network:
Windows XP
Database:
Visual FoxPro
Miscellaneous
Thread ID:
01268865
Message ID:
01269970
Views:
11
>>>>>>Is that correct? I thought that SQL aliases have nothing to do with A-J aliases for work areas.
>>>>>>
>>>>>>>It's a bad idea to use one leter meaningless table aliases in a query. It makes the query totally unreadable. It also could be dangerous because letters A-J are reserved for workareas 1-10.
>>>>>
>>>>>From my testing, you are correct: Message#1154483
>>>>
>>>>It's no longer a problem, but at one time, you could get unexpected results with something along these lines:
>>>>
>>>>
>>>>SELECT 1
>>>>USE MyTable && now in workarea A
>>>>
>>>>SELECT ... ;
>>>>  FROM AnotherTable A ;
>>>>  ...
>>>>
>>>>
>>>>VFP would get confused over what A meant.
>>>
>>>Well, my understanding is that the *idea* behind the SQL engine has been complete isolation, for a very long time. For example, the warnings about using UDFs in SQL commands (in VFP9 help, "Considerations for SQL Select Statements") have been there for a long time (i.e. in a lot of earlier versions).
>>>
>>>During development and testing I've occasionally seen weird errors using single-letter aliases, but for me it's always been caused by a violation of the rules set forth in the Help section referenced above.
>>>
>>>I suppose there could be a *bug* in one or more VFP version(s) that might make it act up as you describe. I have some heavily-used VFP apps that do some serious data munging in VFP5, using single-letter aliases and I've never had a reported problem. I'd be interested in knowing if anyone else has run into any problems, or has some repro code that shows any such problem in VFP5 or later.
>>
>>I used to know how to reproduce this one, but it's been several versions since they fixed it. There definitely was such a bug at one time in the VFP era.
>
>I happen to own HackFox 3, and on page 652 you & Ted give the same warning. Maybe Ted remembers, or maybe it was specific to VFP3? (which I don't consider a "real" version of VFP, anyways :))

Yep, I'm not surprised it's there. I doubt Ted will remember, since I wrote that section. I see the same warning in Hack 7, but I'm sure I didn't retest it there. My vague memory is that it was fixed somewhere in the VFP 5/6 era.

Tamar
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