Provide documentation of expose APIs to enable handling of type coercion at UNION plan construction. #12142
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…ly pub interfaces
…nvolved in type coercion
…ess type coercion
github-actions
bot
added
logical-expr
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Note to @alamb -- exposing the rewriter api (as suggested here), enables the union type-coercion with less of the schema shenangians and overhead (vs the full analyzer). Gives the user options. |
comphead
reviewed
Aug 24, 2024
comphead
reviewed
Aug 24, 2024
| /// or alternatively, merge the union input schema using [`coerce_union_schema`] and | ||
| /// apply the expression rewrite with [`coerce_plan_expr_for_schema`]. | ||
| /// | ||
| /// [`TypeCoercionRewriter::coerce_union`]: https://docs.rs/datafusion-optimizer/latest/datafusion_optimizer/analyzer/type_coercion/struct.TypeCoercionRewriter.html#method.coerce_union |
@comphead -- I'm not sure which error message you are referring to? 😅 🙏🏼 |
Ignore it, for downstream projects not using the optimizer it would be difficult to understand why UNION crashed, but I believe the documentation is enough |
alamb
reviewed
Aug 26, 2024
| @@ -56,6 +56,8 @@ use datafusion_expr::{ | |||
| Projection, ScalarUDF, Union, WindowFrame, WindowFrameBound, WindowFrameUnits, | |||
| }; | |||
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| /// Performs type coercion by determining the schema | |||
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Which issue does this PR close?
Closes #12105
Rationale for this change
We construct our own logical plans for a SQL-derivative languages (e.g. InfluxQL). The construction of logic plans using UNION requires that upon construction of the union plan node, we type-coerce the expressions prior to building the rest of the plan. If we don't perform this expression rewrite, then our consuming LIMIT, GROUP BY, ORDER BY, and aggregates will not be built properly.
We do not think our use case is unique, and therefore we are (a) exposing the APIs need to perform this coercion and (b) providing docs.
What changes are included in this PR?
coerce_union_schemaTypeCoercionTypeCoercionRewritercoerce_union_schema.union()API, which does the logical plan construction , as to the how/when/why to use type coercion.Are these changes tested?
No code changes.
Are there any user-facing changes?
No. Only more exposed interfaces to use.