Merging a array of queries into a single query

Question

I want to merge an array of queries into one query

I have tried this

<cfquery name="MergedData" dbtype="query">
    <cfloop from="1" to="#arrayLen(arData)#" index="k"> 
        SELECT *
        FROM    arData[k]
        <cfif k LT ArrayLen(arData)>UNION</cfif>
    </cfloop>
    ORDER BY EID
</cfquery>

I get an error that looks like

<br><b>Query Of Queries syntax error.</b><br> Encountered "[k]. 

Answer 1

This is what end up working

<cfquery name="local.qryMergedData" dbtype="query">
    <cfloop array="#arguments.Data#" index="k">
        <cfset local.currentIndex++>
        <cfset setvariable("Data_#local.currentIndex#", k)>

        SELECT *
        FROM   Data_#local.currentIndex#
        <cfif local.currentIndex LT local.MaxIndex>UNION</cfif>
    </cfloop>
    ORDER BY EID
</cfquery>  

I really don't like that I am setting a variable inside of a <cfquery>, but at least it is only one query

Answer 2

Try an alternative way of looping over your array. You need to create your own counter though to figure out the logic of if you need to keep appending 'UNION' to your SQL statement.

<cfset i = 1>
<cfquery name="MergedData" dbtype="query">
    <cfloop index="k" array="#arData#"> 
        SELECT *
        FROM    k
        <cfif i LT ArrayLen(arData)>UNION</cfif>
        <cfset i++>
    </cfloop>
    ORDER BY EID
</cfquery>

NB: you wouldn't need to calculate a counter yourself if you're using Railo instead of Adobe CF, as you can then do both index and item like so, as Peter mentioned in the comments above:

<cfloop index="i" item="k" array="#arData#"> 

Answer 3

If you'd like to accomplish this with functional programming, you could use the Underscore.cfc library (requires CF 10+ or Railo 4+):

// instantiate Underscore library
_ = new Underscore();

// convert the array of queries to a single array of structs
mergedArray = _.reduce(arrayOfQueries, function (memo, query) {
  // convert current query to an array of structs
  //   and concatenate it to the rest of the result
  return _.concat(memo, _.toArray(query));
}, []);

// convert the array of structs back to a query
mergedQuery = _.toQuery(mergedArray);

This solution utilizes reduce() to combine the array of queries into a single array of structs. The anonymous function passed to reduce() converts each query in the array of queries to an array of structs using toArray(), then concatenates that array with the rest of the array of structs (the memo value).

Once the array of queries has been converted to a single array of structs, it is a simple matter to convert it back to a query using toQuery() (assuming that is necessary).

Note: I wrote the Underscore library

Answer 4

Try like this:

    <cfsavecontent variable="testing">
    <cfset j = 1>
    <cfloop array="#test#" index="i">
        SELECT id FROM #i# LIMIT 10
        <cfif j LT ArrayLen(test)> UNION </cfif>
        <cfset j++>
    </cfloop>
</cfsavecontent>

<cfquery name="qTest" datasource="#application.dsn#">
    #testing#
</cfquery>