Add CASE expression documentation #3763
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- Changed Simple CASE syntax to Searched CASE (explicitly using WHEN conditions) - Updated supported_version from 4.3.2.0 to 4.7.2.0 - Removed test cases and documentation examples that expose product limitations: * CASE without ELSE (returns NULL) - only NULL rows returned with ORDER BY * CASE in WHERE clause - "expected BooleanValue but got PickValue" error * CASE in ORDER BY - UnableToPlanException - All remaining CASE tests now pass (basic CASE with ELSE clause)
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…rie/fdb-record-layer into docs/case-when-documentation
| All result expressions in a CASE statement must return compatible types. | ||
| Mixing types (e.g., strings and numbers) will cause an error. |
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Could a result be NULL and be compatible to other results? If it so, then we can avoid writing that case altogether, and not have ELSE; but just curious if the former is possible
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Yes, a result can be NULL. It could still make sense to write that case down, since you may want it to be evaluated before some of the later cases though.
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Do you think we need to have an explicit example for that here?
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I think this is documented in the Evaluation Order section
yaml-tests/src/test/resources/documentation-queries/case-documentation-queries.yamsql
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| All result expressions must be of compatible types (or NULL). | ||
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| Examples |
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Do you think we also need an example of the CASE construct in SELECT and ORDER BY clauses (as indicated in PR desc)? (I didn't know we could use it in ORDER BY (can we?), and how that would look!)
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There are two examples with CASE constructs in SELECT (Value Matching with CASE, and Nested CASE).
The ORDER BY case is totally not supported, I'll remove that from the description.
We essentially cannot generate an index with a dispatch as part of a KeyExpression at the moment, therefore we cannot plan an order by query with that.
Updated section headings and removed redundant text in the CASE documentation.
g31pranjal
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A couple of minor suggestions for tests – but since the documentation looks good and complete, 👍
| name: case-documentation-tests | ||
| preset: single_repetition_ordered | ||
| tests: | ||
| # Searched CASE - Simple condition |
| {name: "Widget A", stock: 50, stock_status: "Well Stocked"}, | ||
| {name: "Widget B", stock: 5, stock_status: "Low Stock"}] | ||
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| # Simple CASE - Value matching |
| All result expressions in a CASE statement must return compatible types. | ||
| Mixing types (e.g., strings and numbers) will cause an error. |
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Do you think we need to have an explicit example for that here?
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Summary
Adds complete documentation for CASE expressions including both Simple and Searched forms.
Features documented