[CALCITE-7428] Support regexp function change regexp operator for Hive library

core/src/main/java/org/apache/calcite/sql/dialect/HiveSqlDialect.java

@@ -129,6 +129,9 @@ public HiveSqlDialect(Context context) {
     case TRIM:
       RelToSqlConverterUtil.unparseHiveTrim(writer, call, leftPrec, rightPrec);
       break;
+    case RLIKE:
+      RelToSqlConverterUtil.unparseRegexp(writer, call, leftPrec, rightPrec);
+      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }

core/src/main/java/org/apache/calcite/sql/fun/SqlLibraryOperators.java

@@ -705,11 +705,10 @@ static RelDataType deriveTypeSplit(SqlOperatorBinding operatorBinding,
   public static final SqlFunction REGEXP_SUBSTR = REGEXP_EXTRACT.withName("REGEXP_SUBSTR");
 
   /** The "REGEXP(value, regexp)" function, equivalent to {@link #RLIKE}. */
-  @LibraryOperator(libraries = {SPARK})
+  @LibraryOperator(libraries = {SPARK, HIVE})
   public static final SqlFunction REGEXP =
-      SqlBasicFunction.create("REGEXP", ReturnTypes.BOOLEAN_NULLABLE,
-          OperandTypes.STRING_STRING,
-          SqlFunctionCategory.STRING);
+      SqlBasicFunction.create("REGEXP", SqlKind.RLIKE, ReturnTypes.BOOLEAN_NULLABLE,
+          OperandTypes.STRING_STRING);
 
   /** The "REGEXP_LIKE(value, regexp)" function, equivalent to {@link #RLIKE}. */
   @LibraryOperator(libraries = {SPARK, MYSQL, POSTGRESQL, ORACLE})

core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java

@@ -445,4 +445,19 @@ public ClickHouseSqlArrayTypeNameSpec(SqlTypeNameSpec elementTypeName,
       writer.endList(frame);
     }
   }
+
+  /**
+   * Unparses REGEXP function calls by converting from function call format
+   * (e.g., REGEXP(column, pattern)) to infix operator format (e.g., column REGEXP pattern).
+   */
+  public static void unparseRegexp(SqlWriter writer, SqlCall call, int leftPrec, int rightPrec) {
+    if ("REGEXP".equals(call.getOperator().getName())) {
+      final SqlWriter.Frame frame = writer.startList(SqlWriter.FrameTypeEnum.SIMPLE, "(", ")");
+      call.operand(0).unparse(writer, leftPrec, rightPrec);
+      writer.sep("REGEXP", true);
+      call.operand(1).unparse(writer, leftPrec, rightPrec);
+      writer.endList(frame);
+    }
+  }
+
 }

core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java

@@ -11761,4 +11761,36 @@ public Sql schema(CalciteAssert.SchemaSpec schemaSpec) {
         .ok(expected);
   }
 
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-7428">[CALCITE-7428]
+   * Support regexp function change regexp operator for Hive library</a>. */
+  @Test void testRegexpWithHive() {
+    final String query = "select \"brand_name\"\n"
+        + "from \"product\" where REGEXP(\"brand_name\",'[a-zA-Z]') ";
+    final String expectedHive = "SELECT `brand_name`\nFROM "
+        + "`foodmart`.`product`\nWHERE (`brand_name` REGEXP '[a-zA-Z]')";
+    sql(query).withLibrary(SqlLibrary.HIVE).withHive().ok(expectedHive);
+  }
+
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-7428">[CALCITE-7428]
+   * Support regexp function change regexp operator for Hive library</a>. */
+  @Test void testRegexpWithHiveIsNotNull() {
+    final String query = "select \"brand_name\"\n"
+        + "from \"product\" where REGEXP(\"brand_name\",'[a-zA-Z]') is not null ";
+    final String expectedHive = "SELECT `brand_name`\nFROM "
+        + "`foodmart`.`product`\nWHERE (`brand_name` REGEXP '[a-zA-Z]') IS NOT NULL";
+    sql(query).withLibrary(SqlLibrary.HIVE).withHive().ok(expectedHive);
+  }
+
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-7428">[CALCITE-7428]
+   * Support regexp function change regexp operator for Hive library</a>. */
+  @Test void testSelectRegexpWithHiveIsNotNull() {
+    final String query = "select REGEXP(\"brand_name\",'[a-zA-Z]') is not null \n"
+        + "from \"product\"";
+    final String expectedHive = "SELECT (`brand_name` REGEXP '[a-zA-Z]') IS NOT NULL\n"
+        + "FROM `foodmart`.`product`";
+    sql(query).withLibrary(SqlLibrary.HIVE).withHive().ok(expectedHive);
+  }
 }

site/_docs/reference.md

@@ -3004,7 +3004,7 @@ In the following:
 | b s | POW(numeric1, numeric2)                      | Returns *numeric1* raised to the power *numeric2*
 | b c h q m o f s p r | POWER(numeric1, numeric2) | Returns *numeric1* raised to the power of *numeric2*
 | p r | RANDOM()                                     | Generates a random double between 0 and 1 inclusive
-| s | REGEXP(string, regexp)                         | Equivalent to `string1 RLIKE string2`
+| s h | REGEXP(string, regexp)                         | Equivalent to `string1 RLIKE string2`
 | b | REGEXP_CONTAINS(string, regexp)                | Returns whether *string* is a partial match for the *regexp*
 | b | REGEXP_EXTRACT(string, regexp [, position [, occurrence]]) | Returns the substring in *string* that matches the *regexp*, starting search at *position* (default 1), and until locating the nth *occurrence* (default 1). Returns NULL if there is no match
 | b | REGEXP_EXTRACT_ALL(string, regexp)             | Returns an array of all substrings in *string* that matches the *regexp*. Returns an empty array if there is no match

testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java

@@ -4232,6 +4232,7 @@ void checkIsNull(SqlOperatorFixture f, SqlOperator operator) {
     checkRlikeFunc(f, SqlLibrary.HIVE, SqlLibraryOperators.RLIKE);
     checkRlikeFunc(f, SqlLibrary.SPARK, SqlLibraryOperators.RLIKE);
     checkRlikeFunc(f, SqlLibrary.SPARK, SqlLibraryOperators.REGEXP);
+    checkRlikeFunc(f, SqlLibrary.HIVE, SqlLibraryOperators.REGEXP);
     checkRlikeFunc(f, SqlLibrary.MYSQL, SqlLibraryOperators.RLIKE);
     checkNotRlikeFunc(f.withLibrary(SqlLibrary.HIVE));
     checkNotRlikeFunc(f.withLibrary(SqlLibrary.SPARK));