Woody,
thanks for the examples! Every time that I think a command in VFP is
'useless' someone shows me a cool use for it. Allways learning!
Anthony
> -----Original Message-----
> From: Juergen Wondzinski [mailto:woody /at/ prolib .DO.T de]
> Sent: Friday, April 30, 2004 6:38 AM
> To: profoxtech@leafe.com
> Subject: AW: Where did 'Unique' index type go to?
>
>
> Hi,
>
> A UNIQUE index is/was the dBase way of doing a SELECT DISTINCT.
> Unfortunately, the name "unique" implies something like the
> Primary Index to
> most uneducated users, therefor MS decided to remove that
> index from the
> Dropdown.
>
> Examples for the usage? Easy:
>
> USE Customers
> Index on country unique to temp.idx
> Browse fields country
>
> Shows each country one time. Similar to :
> SELECT DISTINCT Country FROM Customers ORDER BY Country.
>
> ------
> A more sophisticated usage for deduping data. Imagine you get
> a whole bunch
> of addresses from various sources and just append them all
> into one big dbf.
> You now ave to get this data to keep only one record for any address.
>
> SET DELE OFF
> USE TheBigTable
> DELETE ALL
> INDEX ON Name + city + street UNIQUE to Temp.idx
> RECALL ALL
> BROWSE
>
> The trick is, that the Unique index processes only the very
> first occurence
> of the duplicate records, which then gets recalled. All other
> duplicates
> stay deleted and can get packed etc.
>
>
> There are several other usages for UNIQUE, some of them provide a much
> higher performance than the usual SQL variants. But I agree: UNIQUE is
> nothing you wouldadd permanently to a table. It's for
> one-time-usage only.
>
>
>
> Servus
>
> wOOdy
>
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>
>
>
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©2004 Anthony Testi |
