Efficient selection of "all" rows

Efficient selection of "all" rows

The front-end system has "ALL" as a dropdown option. I do not want to blow out the "ALL" into individual elements because it will potentially increase my database 100-fold. My other options are to write the SQL to look for both the actual value (eg. US) and then look for "ALL", but that would be too slow for our system. Is there any way solve this problem elegantly? eg. Country dropdown - All, US, FR, etc

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A front-end system with a dropdown implies a backend script that generates the SQL based on the value passed over in the form's dropdown field. The best way to handle the situation is to put a conditional statement into the script that tests for the ALL value and avoids generating the WHERE clause. Here's how it might look in ColdFusion --

<CFQUERY NAME="queryname" DATASOURCE="#ds#">
  select *
    from yourTable
 <CFIF form.country IS "ALL">
 <CFELSE>
   where country = '#form.country#'
 </CFIF>
</CFQUERY>

Note that when the form's country field value is ALL, the WHERE clause is not generated, so the query will return all rows.

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This was first published in March 2002

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