Support ExistsSubquery in PPL

[LantaoJin]

Description

ExistsSubquery usage

Assumptions: a, b are fields of table outer, c, d are fields of table inner, e, f are fields of table inner2

• source = outer | where exists [ source = inner | where a = c ]
• source = outer | where not exists [ source = inner | where a = c ]
• source = outer | where exists [ source = inner | where a = c and b = d ]
• source = outer | where not exists [ source = inner | where a = c and b = d ]
• source = outer | where exists [ source = inner1 | where a = c and exists [ source = inner2 | where c = e ] ] (nested)
• source = outer | where exists [ source = inner1 | where a = c | where exists [ source = inner2 | where c = e ] ] (nested)
• source = outer | where exists [ source = inner | where c > 10 ] (uncorrelated exists)
• source = outer | where not exists [ source = inner | where c > 10 ] (uncorrelated exists)
• source = outer | where exists [ source = inner ] | eval l = "nonEmpty" | fields l (special uncorrelated exists)

SQL Migration examples with Exists-Subquery PPL:

tpch q4 (exists subquery with aggregation)

select
  o_orderpriority,
  count(*) as order_count
from
  orders
where
  o_orderdate >= date '1993-07-01'
  and o_orderdate < date '1993-07-01' + interval '3' month
  and exists (
    select
      l_orderkey
    from
      lineitem
    where l_orderkey = o_orderkey
      and l_commitdate < l_receiptdate
  )
group by
  o_orderpriority
order by
  o_orderpriority

Rewritten by PPL ExistsSubquery query:

source = orders
| where o_orderdate >= "1993-07-01" and o_orderdate < "1993-10-01"
    and exists [
      source = lineitem
      | where l_orderkey = o_orderkey and l_commitdate < l_receiptdate
    ]
| stats count(1) as order_count by o_orderpriority
| sort o_orderpriority
| fields o_orderpriority, order_count

Issues Resolved

Resolve #711 as a sub-task of #661

Check List

• Updated documentation (ppl-spark-integration/README.md)
• Implemented unit tests
• Implemented tests for combination with other commands
• Commits are signed per the DCO using --signoff

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[YANG-DB]

@LantaoJin plz resolve minor conflict
thanks