improve SQL Eval support

src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java

@@ -56,16 +56,25 @@ import com.alibaba.druid.sql.dialect.oracle.visitor.OracleEvalVisitor;
 import com.alibaba.druid.sql.dialect.postgresql.visitor.PGEvalVisitor;
 import com.alibaba.druid.sql.dialect.sqlserver.visitor.SQLServerEvalVisitor;
 import com.alibaba.druid.sql.visitor.functions.Ascii;
+import com.alibaba.druid.sql.visitor.functions.Bin;
+import com.alibaba.druid.sql.visitor.functions.BitLength;
+import com.alibaba.druid.sql.visitor.functions.Char;
 import com.alibaba.druid.sql.visitor.functions.Concat;
+import com.alibaba.druid.sql.visitor.functions.Elt;
 import com.alibaba.druid.sql.visitor.functions.Function;
 import com.alibaba.druid.sql.visitor.functions.Hex;
+import com.alibaba.druid.sql.visitor.functions.Insert;
 import com.alibaba.druid.sql.visitor.functions.Instr;
 import com.alibaba.druid.sql.visitor.functions.Lcase;
 import com.alibaba.druid.sql.visitor.functions.Left;
 import com.alibaba.druid.sql.visitor.functions.Length;
+import com.alibaba.druid.sql.visitor.functions.Locate;
+import com.alibaba.druid.sql.visitor.functions.Lpad;
+import com.alibaba.druid.sql.visitor.functions.Ltrim;
 import com.alibaba.druid.sql.visitor.functions.Now;
 import com.alibaba.druid.sql.visitor.functions.Reverse;
 import com.alibaba.druid.sql.visitor.functions.Right;
+import com.alibaba.druid.sql.visitor.functions.Substring;
 import com.alibaba.druid.sql.visitor.functions.Trim;
 import com.alibaba.druid.sql.visitor.functions.Ucase;
 import com.alibaba.druid.sql.visitor.functions.Unhex;
@@ -149,13 +158,26 @@ public class SQLEvalVisitorUtils {
     static void registerBaseFunctions() {
         functions.put("now", Now.instance);
         functions.put("concat", Concat.instance);
+        functions.put("concat_ws", Concat.instance);
         functions.put("ascii", Ascii.instance);
+        functions.put("bin", Bin.instance);
+        functions.put("bit_length", BitLength.instance);
+        functions.put("insert", Insert.instance);
         functions.put("instr", Instr.instance);
+        functions.put("char", Char.instance);
+        functions.put("elt", Elt.instance);
         functions.put("left", Left.instance);
+        functions.put("locate", Locate.instance);
+        functions.put("lpad", Lpad.instance);
+        functions.put("ltrim", Ltrim.instance);
+        functions.put("mid", Substring.instance);
+        functions.put("substring", Substring.instance);
         functions.put("right", Right.instance);
         functions.put("reverse", Reverse.instance);
         functions.put("len", Length.instance);
         functions.put("length", Length.instance);
+        functions.put("char_length", Length.instance);
+        functions.put("character_length", Length.instance);
         functions.put("trim", Trim.instance);
         functions.put("ucase", Ucase.instance);
         functions.put("upper", Ucase.instance);
@@ -172,6 +194,7 @@ public class SQLEvalVisitorUtils {
 
         if (function != null) {
             Object result = function.eval(visitor, x);
+            
             if (result != SQLEvalVisitor.EVAL_ERROR) {
                 x.getAttributes().put(EVAL_VALUE, result);
             }
@@ -721,7 +744,7 @@ public class SQLEvalVisitorUtils {
             SQLExpr leftEvalExpr = (SQLExpr) left.getAttribute(EVAL_EXPR);
             SQLExpr rightEvalExpr = (SQLExpr) right.getAttribute(EVAL_EXPR);
 
-            if (leftEvalExpr.equals(rightEvalExpr)) {
+            if (leftEvalExpr != null && leftEvalExpr.equals(rightEvalExpr)) {
                 switch (x.getOperator()) {
                     case Like:
                     case Equality:

src/main/java/com/alibaba/druid/sql/visitor/SchemaStatVisitor.java

@@ -562,6 +562,10 @@ public class SchemaStatVisitor extends SQLASTVisitorAdapter {
     }
 
     public boolean visit(SQLSelectQueryBlock x) {
+        if (x.getFrom() == null) {
+            return false;
+        }
+        
         setMode(x, Mode.Select);
 
         if (x.getFrom() instanceof SQLSubqueryTableSource) {

src/main/java/com/alibaba/druid/sql/visitor/functions/Bin.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.visitor.functions;
+
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+
+public class Bin implements Function {
+
+    public final static Bin instance = new Bin();
+
+    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
+        if (x.getParameters().size() != 1) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        SQLExpr param0 = x.getParameters().get(0);
+        param0.accept(visitor);
+
+        Object param0Value = param0.getAttributes().get(EVAL_VALUE);
+        if (param0Value == null) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        if (param0Value instanceof Number) {
+            long longValue = ((Number) param0Value).longValue();
+            String result = Long.toString(longValue, 2);
+            return result;
+        }
+        return SQLEvalVisitor.EVAL_ERROR;
+    }
+}

src/main/java/com/alibaba/druid/sql/visitor/functions/BitLength.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.visitor.functions;
+
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+
+public class BitLength implements Function {
+
+    public final static BitLength instance = new BitLength();
+
+    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
+        if (x.getParameters().size() != 1) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        SQLExpr param0 = x.getParameters().get(0);
+        param0.accept(visitor);
+
+        Object param0Value = param0.getAttributes().get(EVAL_VALUE);
+        if (param0Value == null) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        if (param0Value instanceof String) {
+            return ((String) param0Value).getBytes().length * 8;
+        }
+        return SQLEvalVisitor.EVAL_ERROR;
+    }
+}

src/main/java/com/alibaba/druid/sql/visitor/functions/Char.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.visitor.functions;
+
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
+
+import java.math.BigDecimal;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+
+public class Char implements Function {
+
+    public final static Char instance = new Char();
+
+    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
+        if (x.getParameters().size() == 0) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        StringBuffer buf = new StringBuffer(x.getParameters().size());
+        for (SQLExpr param : x.getParameters()) {
+            param.accept(visitor);
+
+            Object paramValue = param.getAttributes().get(EVAL_VALUE);
+
+            if (paramValue instanceof Number) {
+                int charCode = ((Number) paramValue).intValue();
+                buf.append((char) charCode);
+            } else if (paramValue instanceof String) {
+                int charCode = new BigDecimal((String)paramValue).intValue();
+                buf.append((char) charCode);
+            } else {
+                return SQLEvalVisitor.EVAL_ERROR;
+            }
+        }
+
+        return buf.toString();
+    }
+}

src/main/java/com/alibaba/druid/sql/visitor/functions/Elt.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.visitor.functions;
+
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+
+public class Elt implements Function {
+
+    public final static Elt instance = new Elt();
+
+    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
+        if (x.getParameters().size() <= 1) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        SQLExpr param0 = x.getParameters().get(0);
+        param0.accept(visitor);
+
+        Object param0Value = param0.getAttributes().get(EVAL_VALUE);
+        int param0IntValue;
+        if (!(param0Value instanceof Number)) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+        param0IntValue = ((Number) param0Value).intValue();
+
+        if (param0IntValue >= x.getParameters().size()) {
+            return null;
+        }
+
+        SQLExpr item = x.getParameters().get(param0IntValue);
+        item.accept(visitor);
+
+        Object itemValue = item.getAttributes().get(EVAL_VALUE);
+        return itemValue;
+    }
+}

src/main/java/com/alibaba/druid/sql/visitor/functions/Hex.java

@@ -17,12 +17,11 @@ package com.alibaba.druid.sql.visitor.functions;
 
 import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
 
-import org.apache.xerces.impl.dv.util.HexBin;
-
 import com.alibaba.druid.sql.ast.SQLExpr;
 import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
 import com.alibaba.druid.sql.parser.ParserException;
 import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+import com.alibaba.druid.util.HexBin;
 
 public class Hex implements Function {
 

src/main/java/com/alibaba/druid/sql/visitor/functions/Insert.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.visitor.functions;
+
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+
+public class Insert implements Function {
+
+    public final static Insert instance = new Insert();
+
+    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
+        if (x.getParameters().size() != 4) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        SQLExpr param0 = x.getParameters().get(0);
+        SQLExpr param1 = x.getParameters().get(1);
+        SQLExpr param2 = x.getParameters().get(2);
+        SQLExpr param3 = x.getParameters().get(3);
+        param0.accept(visitor);
+        param1.accept(visitor);
+        param2.accept(visitor);
+        param3.accept(visitor);
+
+        Object param0Value = param0.getAttributes().get(EVAL_VALUE);
+        Object param1Value = param1.getAttributes().get(EVAL_VALUE);
+        Object param2Value = param2.getAttributes().get(EVAL_VALUE);
+        Object param3Value = param3.getAttributes().get(EVAL_VALUE);
+
+        if (!(param0Value instanceof String)) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+        if (!(param1Value instanceof Number)) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+        if (!(param2Value instanceof Number)) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+        if (!(param3Value instanceof String)) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        String str = (String) param0Value;
+        int pos = ((Number) param1Value).intValue();
+        int len = ((Number) param2Value).intValue();
+        String newstr = (String) param3Value;
+        
+        if (pos <= 0) {
+            return str;
+        }
+        
+        if (pos == 1) {
+            if (len > str.length()) {
+                return newstr;
+            }
+            return newstr + str.substring(len);
+        }
+        
+        String first = str.substring(0, pos - 1);
+        if (pos + len - 1 > str.length()) {
+            return first + newstr;
+        }
+        
+        return first + newstr + str.substring(pos + len - 1);
+    }
+}

src/main/java/com/alibaba/druid/sql/visitor/functions/Locate.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.visitor.functions;
+
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
+
+import java.util.List;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+
+public class Locate implements Function {
+
+    public final static Locate instance = new Locate();
+
+    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
+        List<SQLExpr> params = x.getParameters();
+        int paramSize = params.size();
+        if (paramSize != 2 && paramSize != 3) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        SQLExpr param0 = params.get(0);
+        SQLExpr param1 = params.get(1);
+        SQLExpr param2 = null;
+
+        param0.accept(visitor);
+        param1.accept(visitor);
+        if (paramSize == 3) {
+            param2 = params.get(2);
+            param2.accept(visitor);
+        }
+
+        Object param0Value = param0.getAttributes().get(EVAL_VALUE);
+        Object param1Value = param1.getAttributes().get(EVAL_VALUE);
+        if (param0Value == null || param1Value == null) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        String strValue0 = param0Value.toString();
+        String strValue1 = param1Value.toString();
+
+        if (paramSize == 2) {
+            int result = strValue1.indexOf(strValue0) + 1;
+            return result;
+        }
+        
+        Object param2Value = param2.getAttributes().get(EVAL_VALUE);
+        int start = ((Number) param2Value).intValue();
+        
+        int result = strValue1.indexOf(strValue0, start + 1) + 1;
+        return result;
+    }
+}

src/main/java/com/alibaba/druid/sql/visitor/functions/Lpad.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.visitor.functions;
+
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
+
+import java.util.List;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+
+public class Lpad implements Function {
+
+    public final static Lpad instance = new Lpad();
+
+    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
+        List<SQLExpr> params = x.getParameters();
+        int paramSize = params.size();
+        if (paramSize != 3) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        SQLExpr param0 = params.get(0);
+        SQLExpr param1 = params.get(1);
+        SQLExpr param2 = params.get(2);
+
+        param0.accept(visitor);
+        param1.accept(visitor);
+        param2.accept(visitor);
+
+        Object param0Value = param0.getAttributes().get(EVAL_VALUE);
+        Object param1Value = param1.getAttributes().get(EVAL_VALUE);
+        Object param2Value = param2.getAttributes().get(EVAL_VALUE);
+        if (param0Value == null || param1Value == null || param2Value == null) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        String strValue0 = param0Value.toString();
+        int len = ((Number) param1Value).intValue();
+        String strValue1 = param2Value.toString();
+        
+        String result = strValue0;
+        if (result.length() > len) {
+            return result.substring(0, len);
+        }
+        
+        while (result.length() < len) {
+            result = strValue1 + result;
+        }
+
+        return result;
+    }
+}

src/main/java/com/alibaba/druid/sql/visitor/functions/Ltrim.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.visitor.functions;
+
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+
+public class Ltrim implements Function {
+
+    public final static Ltrim instance = new Ltrim();
+
+    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
+        if (x.getParameters().size() != 1) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        SQLExpr param0 = x.getParameters().get(0);
+        param0.accept(visitor);
+
+        Object param0Value = param0.getAttributes().get(EVAL_VALUE);
+        if (param0Value == null) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        String strValue = param0Value.toString();
+        
+        int index = -1;
+        for (int i = 0; i < strValue.length(); ++i) {
+            if (!Character.isWhitespace(strValue.charAt(i))) {
+                index = i;
+                break;
+            }
+        }
+        
+        if (index <= 0) {
+            return strValue;
+        } else {
+            return strValue.substring(index);
+        }
+    }
+}

src/main/java/com/alibaba/druid/sql/visitor/functions/Substring.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.visitor.functions;
+
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
+
+import java.util.List;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+
+public class Substring implements Function {
+
+    public final static Substring instance = new Substring();
+
+    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
+        List<SQLExpr> params = x.getParameters();
+        int paramSize = params.size();
+        if (paramSize != 2 && paramSize != 3) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        SQLExpr param0 = params.get(0);
+        SQLExpr param1 = params.get(1);
+        param0.accept(visitor);
+        param1.accept(visitor);
+
+        Object param0Value = param0.getAttributes().get(EVAL_VALUE);
+        Object param1Value = param1.getAttributes().get(EVAL_VALUE);
+        if (param0Value == null || param1Value == null) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        String str = param0Value.toString();
+        int index = ((Number) param1Value).intValue();
+
+        if (paramSize == 2) {
+
+            if (index < 0) {
+                int lastIndex = str.length() + index ;
+                return str.substring(lastIndex);
+            }
+
+            return str.substring(index - 1);
+        }
+
+        SQLExpr param2 = params.get(2);
+        param2.accept(visitor);
+        Object param2Value = param2.getAttributes().get(EVAL_VALUE);
+        if (param2Value == null) {
+            return SQLEvalVisitor.EVAL_ERROR;
+        }
+
+        int len = ((Number) param2Value).intValue();
+        
+        String result;
+        if (index < 0) {
+            int lastIndex = str.length() + index ;
+            result = str.substring(lastIndex);
+        } else {
+            result = str.substring(index - 1);
+        }
+        
+        return result.substring(0, len);
+    }
+}

src/main/java/com/alibaba/druid/sql/visitor/functions/Unhex.java

@@ -15,17 +15,15 @@
  */
 package com.alibaba.druid.sql.visitor.functions;
 
-import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
 import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_EXPR;
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
 
 import java.io.UnsupportedEncodingException;
 
-import org.apache.xerces.impl.dv.util.HexBin;
-
 import com.alibaba.druid.sql.ast.SQLExpr;
 import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
-import com.alibaba.druid.sql.parser.ParserException;
 import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
+import com.alibaba.druid.util.HexBin;
 
 public class Unhex implements Function {
 
@@ -33,7 +31,7 @@ public class Unhex implements Function {
 
     public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
         if (x.getParameters().size() != 1) {
-            throw new ParserException("argument's != 1, " + x.getParameters().size());
+            return SQLEvalVisitor.EVAL_ERROR;
         }
 
         SQLExpr param0 = x.getParameters().get(0);