Handle back-references in REGEXP_REPLACE() differently in Oracle mode

h2/src/main/org/h2/engine/Mode.java

@@ -119,6 +119,11 @@ public class Mode {
      */
     public boolean logIsLogBase10;
 
+    /**
+     * The function REGEXP_REPLACE() uses \ for back-references.
+     */
+    public boolean regexpReplaceBackslashReferences;
+
     /**
      * SERIAL and BIGSERIAL columns are not automatically primary keys.
      */
@@ -255,6 +260,7 @@ public class Mode {
         mode.convertOnlyToSmallerScale = true;
         mode.uniqueIndexSingleNullExceptAllColumnsAreNull = true;
         mode.treatEmptyStringsAsNull = true;
+        mode.regexpReplaceBackslashReferences = true;
         mode.supportPoundSymbolForColumnNames = true;
         // Oracle accepts keys of the form <namespace>.*. See
         // https://docs.oracle.com/database/121/JJDBC/jdbcvers.htm#JJDBC29006

h2/src/main/org/h2/expression/Function.java

@@ -1414,6 +1414,29 @@ public class Function extends Expression implements FunctionCall {
         case REGEXP_REPLACE: {
             String regexp = v1.getString();
             String replacement = v2.getString();
+            if (database.getMode().regexpReplaceBackslashReferences) {
+                if ((replacement.indexOf('\\') >= 0) || (replacement.indexOf('$') >= 0)) {
+                    StringBuilder sb = new StringBuilder();
+                    for (int i = 0; i < replacement.length(); i++) {
+                        char c = replacement.charAt(i);
+                        switch (c) {
+                        case '$':
+                            sb.append('\\');
+                            break;
+                        case '\\':
+                            if (i + 1 < replacement.length()) {
+                                c = replacement.charAt(i + 1);
+                                if (c >= '0' && c <= '9') {
+                                    sb.append('$');
+                                    continue;
+                                }
+                            }
+                        }
+                        sb.append(c);
+                    }
+                    replacement = sb.toString();
+                }
+            }
             String regexpMode = v3 == null || v3.getString() == null ? "" :
                     v3.getString();
             int flags = makeRegexpFlags(regexpMode);

h2/src/test/org/h2/test/scripts/functions/string/regex-replace.sql

@@ -17,3 +17,31 @@ select regexp_replace('Sylvain', 'S..', 'TOTO', 'mni') as X;
 > --------
 > TOTOvain
 > rows: 1
+
+set mode oracle;
+
+select regexp_replace('first last', '(\w+) (\w+)', '\2 \1') as X from dual;
+> X
+> ----------
+> last first
+> rows: 1
+
+select regexp_replace('first last', '(\w+) (\w+)', '$2 $1') as X from dual;
+> X
+> -----
+> $2 $1
+> rows: 1
+
+set mode regular;
+
+select regexp_replace('first last', '(\w+) (\w+)', '\2 \1') as X from dual;
+> X
+> ---
+> 2 1
+> rows: 1
+
+select regexp_replace('first last', '(\w+) (\w+)', '$2 $1') as X from dual;
+> X
+> ----------
+> last first
+> rows: 1