Increase the parsing of subquery.
Add LogicalApply and LogicalCorrelatedJoin and LogicalEnforceSingleRow.
(These structures are temporarily in use, in preparation for the follow-up)
LogicalApply:
Apply Node for subquery.
Use this node to display the subquery in the relational algebra tree.
refer to "Orthogonal Optimization of Subqueries and Aggregation"
LogicalCorrelatedJoin:
A relational algebra node with join type converted from apply node to subquery.
LogicalEnforceSingleRow:
Guaranteed to return a result of 1 row.
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