Convert an iteration to recursion - scala

Question

I have an iteration logic that returns a query like this :
val baseQuery = s"select agg_id from quality.QUALITY_AGGREGATOR where job_id = 123 and level ="
val reprocessDate ="2018-10-24"
for( i <- 0 to level){
var currLevelSubQuery=""
if (i==0 ){
currLevelSubQuery= baseQuery + s"$i and agg_value >= '${reprocessDate}'"
}
else{
currLevelSubQuery= baseQuery + s"$i and parent_agg_id in ( $prevLevelSubQuery )"
}
prevLevelSubQuery= currLevelSubQuery
finalQuery = finalQuery + currLevelSubQuery + (if (i<level) " union " else "")
}
It returns a query of this nature for level = 2.
SELECT agg_id
FROM quality.quality_aggregator
WHERE job_id = 123
AND level = 0
AND agg_value >= '2018-10-24'
UNION
SELECT agg_id
FROM quality.quality_aggregator
WHERE job_id = 123
AND level = 1
AND parent_agg_id IN (SELECT agg_id
FROM quality.quality_aggregator
WHERE job_id = 123
AND level = 0
AND agg_value >= '2018-10-24')
UNION
SELECT agg_id
FROM quality.quality_aggregator
WHERE job_id = 123
AND level = 2
AND parent_agg_id IN (SELECT agg_id
FROM quality.quality_aggregator
WHERE job_id = 123
AND level = 1
AND parent_agg_id IN
(SELECT agg_id
FROM quality.quality_aggregator
WHERE job_id = 123
AND level = 0
AND agg_value >=
'2018-10-24'))
I am trying to convert it into a recursive logic like this
val baseQuery = s"select agg_id from quality.QUALITY_AGGREGATOR where job_id = 123 and level ="
val finalQuery = getAggIdSQLGenerator(2,"2018-10-24")
def getAggIdSQLGenerator(level : Int, reprocessDate:String):String={
if (level == 0)
( baseQuery + s"$level and agg_value >= '${reprocessDate}'")
else
{
val subQuery=getAggIdSQLGenerator(level-1 ,reprocessDate)
baseQuery + s"$level and parent_agg_id in (" +subQuery +") union "+ subQuery
}
}
But this is not yielding correct results. What am I missing?

Answer 1

This isn't recursive but I think it's a smaller, cleaner, implementation of what you're after.
val baseQuery = ".... level="
val levelRE = "level=(\\d+)".r.unanchored
val reprocessDate ="2018-10-24"
val av = s" and agg_value >= '${reprocessDate}'"
val pai = " and parent_agg_id in "
val itrs = 3
val query = List.iterate(s"${baseQuery}0$av", itrs) { prevStr =>
val level = prevStr match {
case levelRE(n) => n.toInt + 1
case _ => 0
}
s"$baseQuery$level$pai($prevStr)"
}.mkString(" union ")

Answer 2

The issue is you have added union on every query and you have concatenated subquery 2 times.
This gives your expected output.
val baseQuery = s"select agg_id from quality.QUALITY_AGGREGATOR where job_id = 123 and level ="
val finalQuery = getAggIdSQLGenerator(2, "2018-10-24")
def getAggIdSQLGenerator(level: Int, reprocessDate: String): String = {
if (level == 0) {
baseQuery + s" $level and agg_value >= '${reprocessDate}'"
} else {
val subQuery = getAggIdSQLGenerator(level - 1, reprocessDate)
baseQuery + s" $level and parent_agg_id in (" + subQuery + ")"
}
}
println("UNION " + finalQuery)