Fix \$ handling in REGEXP_REPLACE() in Oracle mode and optimize implementation

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

@@ -1419,22 +1419,11 @@ public class Function extends Expression implements FunctionCall {
                     StringBuilder sb = new StringBuilder();
                     for (int i = 0; i < replacement.length(); i++) {
                         char c = replacement.charAt(i);
-                        switch (c) {
-                        case '$':
+                        if (c == '$') {
                             sb.append('\\');
-                            break;
-                        case '\\':
-                            if (i + 1 < replacement.length()) {
-                                c = replacement.charAt(i + 1);
-                                if (c >= '0' && c <= '9') {
-                                    sb.append('$');
-                                    continue;
-                                }
-                                if (c == '\\') {
-                                    sb.append('\\');
-                                    i++;
-                                }
-                            }
+                        } else if (c == '\\' && ++i < replacement.length()) {
+                            c = replacement.charAt(i);
+                            sb.append(c >= '0' && c <= '9' ? '$' : '\\');
                         }
                         sb.append(c);
                     }

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

@@ -32,6 +32,12 @@ select regexp_replace('first last', '(\w+) (\w+)', '\\2 \1') as X from dual;
 > \2 first
 > rows: 1
 
+select regexp_replace('first last', '(\w+) (\w+)', '\$2 \1') as X from dual;
+> X
+> --------
+> $2 first
+> rows: 1
+
 select regexp_replace('first last', '(\w+) (\w+)', '$2 $1') as X from dual;
 > X
 > -----