Support predicate pushdown on char and decimal type in mongodb

[krvikash]

Release notes

(X) Release notes are required, with the following suggested text:

# Mongo
* Support predicate pushdown on `char` and `decimal` type. ({issue}`18382`)

[Praveen2112]

Apart from this - can we update the tests in TestMongoTypeMapping ?

[krvikash]

As discussed offline, we wanted to fix below two cases. But Decimal128 supports 34 digits precision. and below tests still failing with the current change.

// TODO: Fix NumberFormatException: Conversion to Decimal128 would require inexact rounding
//                .addRoundTrip("decimal(38, 0)", "CAST('27182818284590452353602874713526624977' AS decimal(38, 0))", createDecimalType(38, 0), "CAST('27182818284590452353602874713526624977' AS decimal(38, 0))")
//                .addRoundTrip("decimal(38, 0)", "CAST('-27182818284590452353602874713526624977' AS decimal(38, 0))", createDecimalType(38, 0), "CAST('-27182818284590452353602874713526624977' AS decimal(38, 0))")

[krvikash]

As discussed offline. To ensure 38 precision on the filter should not error, I have added testHighPrecisionDecimalPredicate

[krvikash]

In this case, I was not able to apply pushdown condition.

This is the Explain of the "SELECT * FROM " + table.getName() + " WHERE col = " + predicateValue

Trino version: testversion
Fragment 0 [SINGLE]
    Output layout: [col]
    Output partitioning: SINGLE []
    Output[columnNames = [col]]
    │   Layout: [col:decimal(34,0)]
    │   Estimates: {rows: 0 (0B), cpu: 0, memory: 0B, network: 0B}
    └─ Values[]
           Layout: [col:decimal(34,0)]
           Estimates: {rows: 0 (0B), cpu: 0, memory: 0B, network: 0B}

[vlad-lyutenko]

I am little but missed here, why pushdown is not happening here?
I thought Trino rounds it or pass it as it is and mongo just not able to exact match value with higher pression.
But why pushdown is not happening?

[Praveen2112]

Why is the table scan is replaced with a values node ? Is it due to different precision on both side of expression ? Can we add a comment for it

[Praveen2112]

Can we add additional test case for 34 precision decimal value ?

[krvikash]

Why is the table scan is replaced with a values node ?

I am little but missed here, why pushdown is not happening here?

I am not sure about this. It seems that when the value is 38 precision then it is getting converted into null.

This query does not even reach MongoSession#execute

"SELECT * FROM " + table.getName() + " WHERE col = " + predicateValue

[Praveen2112]

Why is the table scan is replaced with a values node ? Is it due to different precision on both side of expression ? Can we add a comment for it

[Praveen2112]

Can we add additional test case for 34 precision decimal value ?

[vlad-lyutenko]

This PR LGTM, the only thing I missed why pushdown not happens with higher precision values #18382 (comment)

[krvikash]

Thanks @praveen2111, @ebyhr, @vlad-lyutenko for the review. Addressed comments

[krvikash]

This PR LGTM, the only thing I missed why pushdown not happens with higher precision values #18382 (comment)

@vlad-lyutenko, I have added a comment. isFullyPushdown works when there is TableScanNode. But due to precision mismatch in Column type and Predicate value, PushPredicateIntoTableScan#pushFilterIntoTableScan returns ValueNode which can not verify using isFullyPushdown.

            assertThat(query("SELECT * FROM " + table.getName() + " WHERE col %s %s ".formatted(operator, predicateValue)))
                    // With EQUAL operator when column type precision is less than the predicate value's precision,
                    // PushPredicateIntoTableScan#pushFilterIntoTableScan returns ValuesNode. So It not possible to verify isFullyPushedDown.
                    .returnsEmptyResult();

[krvikash]

Thanks, @ebyhr for the review. Addressed comments.

[krvikash]

@Praveen2112, AC

[Praveen2112]

Thanks for working on this.