Add documentation and usability for prepared parameters #7785
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alamb
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Oct 10, 2023
datafusion/core/src/dataframe.rs
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| /// .sql("SELECT a FROM example WHERE b = $1") | ||
| /// .await? | ||
| /// // replace $1 with value 2 | ||
| /// .with_param_values(vec![ScalarValue::from(2i64)])? |
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this tests the DataFrame API and fails without the changes to LogicalPlan::with_param_values
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| impl LogicalPlan { | ||
| /// applies collect to any subqueries in the plan | ||
| /// applies `op` to any subqueries in the plan |
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| /// Find all [`Expr::Placeholder`] in anthis, and try | ||
| /// to infer their [`DataType`] from the context of their use. | ||
| pub fn infer_placeholder_types(self, schema: &DFSchema) -> Result<Expr> { |
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This was moved from the datafusion-sql module as it is not SQL specific, but generic to expressions
| "".into(), | ||
| Some(DataType::Int32), | ||
| )))) | ||
| .filter(col("id").eq(placeholder(""))) |
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here is an example of the new placeholder function being much nicer to use
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cc @NGA-TRAN |
NGA-TRAN
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Oct 13, 2023
| /// ); | ||
| /// # Ok(()) | ||
| /// # } | ||
| /// ``` |
| #[test] | ||
| fn test_non_prepare_statement_should_infer_types() { | ||
| // Non prepared statements (like SELECT) should also have their parameter types inferred | ||
| let sql = "SELECT 1 + $1"; |
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@avantgardnerio might you have time to review (and approve) this PR? I can't merge it without an approval from another committer. |
avantgardnerio
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Oct 15, 2023
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Seems minor and innocuous, and adds a test 👍
jackwener
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Oct 16, 2023
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Oct 16, 2023
jackwener
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Oct 16, 2023
Co-authored-by: jakevin <jakevingoo@gmail.com>
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Thanks @jackwener and @avantgardnerio and @NGA-TRAN |
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Which issue does this PR close?
Closes #7776
related to #7776 and #4539
Rationale for this change
While reviewing #7776, I noticed that the parameter values were not well documented. So I started trying to write documentation examples and in so doing found several usability papercuts
that I I also fixed.
What changes are included in this PR?
LogicalPlan::with_param_valuesand YYY with examplesplaceholdertoexpr_fnfunction to more easily construct placeholdersinfer_placeholder_valuesto Expr, and make it public (so it can be used outside of the context of a SQL statement)LogicalPlan::with_param_valuesto also substitute parameter values for nonPREPAREstatements as wellAre these changes tested?
Yes, new tests / doc comments
Are there any user-facing changes?
Better docs
Note it is still not possible to use PREPARE / EXCUTE from SQL but I think this PR completes the backend code to make it work