Support CTEs in sub-query reducer #1504
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plypaul
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plypaul
changed the title
courtneyholcomb
approved these changes
Nov 6, 2024
| @@ -196,7 +199,7 @@ def _is_simple_source(node: SqlSelectStatementNode) -> bool: | |||
| if select_column.expr.lineage.contains_aggregate_exprs: | |||
| return False | |||
| return ( | |||
| len(node.parent_nodes) <= 1 | |||
| len(node.join_descs) == 0 | |||
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This looks like a behavior change - were there changes to the snapshots from this change alone?
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There were no snapshot changes. This is not a behavior change as without CTEs, the number of parent nodes is 1 + the number of joins.
| @@ -612,10 +615,11 @@ def visit_select_statement_node(self, node: SqlSelectStatementNode) -> SqlQueryP | |||
| # JOIN dim_listings c | |||
| # ON a.listing_id = b.listing_id | |||
|
|
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| assert len(node_with_reduced_parents.parent_nodes) == 1 | |||
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Was there a reason to remove this assertion?
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Yes - since CTEs are modeled as a parent node of a SELECT node, this assertion does not hold.
| @@ -579,6 +578,13 @@ def _rewrite_node_with_join(node: SqlSelectStatementNode) -> SqlSelectStatementN | |||
| select_columns=tuple(clauses_to_rewrite.select_columns), | |||
| from_source=from_source, | |||
| from_source_alias=from_source_alias, | |||
| cte_sources=tuple( | |||
| SqlCteNode.create( | |||
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Should this use cte_source.with_new_select?
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Good catch. with_new_select got added as a convenience method late in the stack.
Previously, "parent nodes" was used for either nodes in the FROM clause or the JOIN clause. With the addition of CTEs that are also considered parent nodes, this renames a few variables / updates some conditionals for clarity.
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This updates the sub-query reducer to support CTEs. The
SELECTstatement in each CTE is treated like aSELECT, and all CTEs are retained. i.e. a CTE is not reduced with another CTE. The CTEs are retained to make mapping to dataflow plan nodes easier in later PRs.