Implement Spark-compatible `regexp_count`

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Valutazione

Difficoltà
4/5
Tempo stimato
3-5 giorni
Idoneità per principianti
25/100
Tipo di issue
Funzionalità
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
rust, sql
Ambito
databases

Direzione di ricerca

Start by reading the existing string functions under crates/spark/src/function/string/, especially the regexp_extract_all implementation, since regexp_count must share its matching core rather than wrap DataFusion's regexpcount.rs. The issue is explicit that the Java-regex compatibility helper proposed for rlike does not exist yet, so confirm with a maintainer whether this work is blocked on it before writing anything. Done means a new regexp_count function with #[user_doc], plus crates/sqllogictest/test_files/string/regexp_count.slt covering the listed edge cases (NULLs, empty pattern, non-overlapping matches, invalid pattern, collation).

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

enhancement

Part of #174 and apache/datafusion-comet#7300.

What the function does

regexp_count(str, regexp) returns the number of times the Java regular expression regexp matches in str. It is RuntimeReplaceable: the analyzer rewrites it to size(regexp_extract_all(str, regexp, 0), legacySizeOfNull = false), so it counts the matches found by repeated Matcher.find(). Available since 3.4.0.

Both arguments are implicitly cast to STRING. Result is INT. NULL if either argument is NULL. There are no start or flags arguments.

Examples
SELECT regexp_count('Steven Jones and Stephen Smith are the best players', 'Ste(v|ph)en');
-- 2
SELECT regexp_count('abcdefghijklmnopqrstuvwxyz', '[a-z]{3}');
-- 8
SELECT regexp_count('1a 2b 14m', '\\d+');
-- 3
SELECT regexp_count('the fox', 'FOX');
-- 0
SELECT regexp_count('the fox', '(?i)FOX');
-- 1
SELECT regexp_count('passwd7 plain A1234 a1234', '(?=[^ ]*[a-z])(?=[^ ]*[0-9])[^ ]+');
-- 2
SELECT regexp_count(null, 'abc');
-- NULL
Edge cases to test
  • NULL str or NULL regexp, literal and column: NULL.
  • Matches are non-overlapping: '[a-z]{3}' over 26 letters is 8.
  • Empty pattern: regexp_count('abc', '') is 4 (one empty match at each of the 4 positions). regexp_count('', '') is 1.
  • Empty matches after a non-empty match: Java counts them, the regex crate does not (its testdata/empty.toml gives 3 matches for b| on abc; Java finds 4). regexp_count('1a 2b 14m', '(\\d+)?') is 9 in Spark (the same matches as the regexp_extract_all golden result ["1","","","2","","","14","",""]).
  • Invalid pattern: INVALID_PARAMETER_VALUE.PATTERN. Because of the rewrite, the functionName in the error is `regexp_extract_all`, not regexp_count.
  • Column patterns (different per row).
  • spark.sql.parser.escapedStringLiterals (default false) only changes how the SQL literal reaches the function. In .slt, DataFusion keeps backslashes literal.
  • Java vs Rust divergences to decline or test: lookaround (the passwd7 example above needs it), backreferences, atomic groups, possessive quantifiers; ASCII \d \w \s in Java vs Unicode in Rust (regexp_count('1\u0663', '\\d'), U+0663 ARABIC-INDIC DIGIT THREE, is 1 in Spark); . excludes \r, \u0085, \u2028, \u2029 in Java; $ matches before a final line terminator in Java (regexp_count('a\n', 'a$') is 1); (?i) ASCII-only in Java (U+212A KELVIN SIGN does not match (?i)k); inline flag letters U, u, d; Java-only \Q..\E, \h, \R, \Z; Rust-only (?P<n>), \<, [[:alpha:]].
  • UTF8_LCASE collation (4.0+) counts case-insensitively.
Differences across Spark versions
  • 4.0: collation-aware input types. Otherwise none found (3.4.0 through 4.2.0).
Implementation notes
  • Spark: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala, RegExpCount (replacement uses RegExpExtractAll and Size).
  • Because of the rewrite, Spark plans (and Comet) never contain RegExpCount; engines that translate Spark plans will see size(regexp_extract_all(...)). A direct regexp_count UDF is still useful for SQL users of datafusion-spark and should share the matching core with regexp_extract_all.
  • DataFusion core regexp_count(str, regexp[, start[, flags]]) (datafusion/functions/src/regex/regexpcount.rs) returns BIGINT, accepts start and flags, and uses Rust regex syntax and Rust empty-match iteration. Do not wrap it unchanged.
  • Use the shared Java-regex compatibility helper proposed for rlike (verified subset, decline otherwise, decided at planning time for literal patterns).
  • Belongs in crates/spark/src/function/string/. Add crates/sqllogictest/test_files/string/regexp_count.slt and document with #[user_doc].

This issue was generated by an LLM (Claude) from the Apache Spark source code and tests. Examples come from Spark's ExpressionDescription examples, test suites and .sql.out golden files, but please verify them against Spark before relying on them.

Lingua principale
Rust
Stelle
7
Fork
15
Merge medio
16h 43m
PR unite (30g)
26

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