loftiest opened a new pull request, #56498:
URL: https://github.com/apache/spark/pull/56498
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### What changes were proposed in this pull request?
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This PR extends the `instr` function to accept optional `start` and
`occurrence` parameters, supporting forward and backward search with full
collation awareness. The changes include:
- A new expression `StringInstr4` that handles 3‑ and 4‑argument
invocations, while the existing two‑argument `instr` continues to use
`StringInstr`.
- A new `StringInstrExpressionBuilder` that routes calls based on the number
of arguments: 2 arguments → `StringInstr`, 3 or 4 arguments → `StringInstr4`.
- Extended `UTF8String.indexOf(pattern, start, occurrence)` with both
forward (positive `start`) and backward (negative `start`) search, using
efficient single‑pass UTF‑8 byte scanning.
- Extended `CollationAwareUTF8String.lowercaseIndexOf` and ICU `indexOf` to
support multi‑occurrence search for `UTF8_BINARY_LCASE` and ICU collations.
- Updated `FunctionRegistry` to use the new `StringInstrExpressionBuilder`.
- New overloads in `functions.scala` and corresponding Python APIs
(`pyspark.sql.functions.builtin`) with proper default‑parameter handling.
- New error class `OCCURRENCE` for invalid (≤ 0) occurrence values.
- Comprehensive unit tests covering binary, lowercase, and ICU collations,
forward/backward/overlapping searches, multi‑byte characters, and boundary
conditions.
The behavior when `substr` is empty remains unchanged (returns `start`
position), preserving backward compatibility with the existing two‑argument
`instr`.
### Why are the changes needed?
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Currently, Spark's `instr` only supports two arguments, forcing users to
write complex workarounds when they need to start searching from a specific
position or find a particular occurrence. Oracle, Impala, and Db2 all provide a
four‑argument `INSTR` with these capabilities. This PR aligns Spark SQL with
those databases, simplifies user queries, and reduces migration friction.
### Does this PR introduce _any_ user-facing change?
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Yes, but only additive.
- New SQL syntax: `instr(str, substr [, start [, occurrence]])` where
`start` and `occurrence` are optional integers (default 1). Negative `start`
performs backward search.
- New Scala/Python API overloads with corresponding optional parameters.
- Error raised when `occurrence <= 0`.
- All existing two‑argument usage remains completely unaffected.
Documentation for the new parameters is included in the expression
description and will be surfaced in SQL function docs.
### How was this patch tested?
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- Added extensive unit tests to `StringFunctionsSuite`,
`CollationAwareUTF8StringSuite`, and `UTF8StringSuite` covering:
- Forward and backward search with multiple occurrences
- Overlapping matches (e.g., `'aa'` in `'aaa'`)
- Multi‑byte and supplementary characters
- Collation scenarios: `UTF8_BINARY`, `UTF8_BINARY_LCASE`, `UNICODE_CI`
(including sigma variants, German `ß`, and Turkish `İ` expansion)
- Boundary conditions (`start = 0`, `occurrence <= 0`, `start` out of
range, empty substring)
- Verified error condition formatting in `SparkThrowableSuite`.
- Verified Python API behavior matches SQL execution through existing
PySpark doctests.
### Was this patch authored or co-authored using generative AI tooling?
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DeepSeek
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