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Speeding up APPEND
Message
From
14/02/2001 12:57:49
Jonathan Cochran
Alion Science and Technology
Maryland, United States
 
 
General information
Forum:
Visual FoxPro
Category:
Databases,Tables, Views, Indexing and SQL syntax
Miscellaneous
Thread ID:
00475722
Message ID:
00475873
Views:
35
You could loop through the indexes in the source table and build an INDEX ON command string for each index. We have similar code that looks something like this:
FOR ln_Loop = 1 TO TAGCOUNT()

   lc_IndexExpression = "INDEX ON " + SYS( 14, ln_Loop ) + " TAG " + ;
      TAG(ln_Loop)

   IF !EMPTY( SYS( 2021, ln_Loop ) )
      lc_IndexExpression = lc_IndexExpression + " FOR " + SYS( 2021, ln_Loop )
   ENDIF

   IF DESCENDING( ln_Loop )
      lc_IndexExpression = lc_IndexExpression + " DESCENDING"
   ENDIF

   IF UNIQUE( ln_Loop )
      lc_IndexExpression = lc_IndexExpression + " UNIQUE"
   ENDIF

   IF CANDIDATE( ln_Loop )
      lc_IndexExpression = lc_IndexExpression + " CANDIDATE"
   ENDIF

ENDFOR
Note that this doesn't work for Primary Key indexes that are created with ALTER TABLE <> ADD PRIMARY KEY ...

>I'm doing this:
>
>
>  SELECT a_sotran
>  COPY STRUCTURE TO (lcTempFile) WITH CDX
>  USE IN a_sotran
>  USE (lcTempFile) ALIAS a_sotran IN 0
>  SELECT a_sotran
>  APPEND FROM (gf_sotranf)
>  APPEND FROM (gf_soytrnf)
>
>
>Basically, I'm making a temp table with the name of the current table that holds the current and history files to fool SBT into accessing them both. The trouble is that the appends are too slow if the indexes are there. They're plenty fast if I drop the "WITH CDX", but I do need the indexes available.
>
>What I'm wondering is if there is some way to attach the indexes after the append, and if that would be faster? I know I can do INDEX ON, but I'd rather not hard code the indexes in case they change in a future version.
>
>Any other suggestions on speeding this up significantly? Those history tables can get really huge, so speed is important.
>
>Thanks,
>
>Michelle
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