tristaZero commented on a change in pull request #8116:
URL: https://github.com/apache/shardingsphere/pull/8116#discussion_r521016162



##########
File path: 
shardingsphere-sql-parser/shardingsphere-sql-parser-dialect/shardingsphere-sql-parser-mysql/src/test/java/org/apache/shardingsphere/sql/parser/mysql/MySQLFormartTest.java
##########
@@ -0,0 +1,91 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.shardingsphere.sql.parser.mysql;
+
+import lombok.Getter;
+import org.antlr.v4.runtime.CodePointBuffer;
+import org.antlr.v4.runtime.CodePointCharStream;
+import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.apache.shardingsphere.sql.parser.core.parser.ParseASTNode;
+import org.apache.shardingsphere.sql.parser.mysql.parser.MySQLLexer;
+import org.apache.shardingsphere.sql.parser.mysql.parser.MySQLParser;
+import 
org.apache.shardingsphere.sql.parser.mysql.visitor.format.impl.MySQLDMLFormatSQLVisitor;
+import 
org.apache.shardingsphere.sql.parser.mysql.visitor.format.impl.MySQLFormatSQLVisitor;
+import org.junit.Test;
+
+import java.nio.CharBuffer;
+import java.util.LinkedList;
+import java.util.List;
+
+import static org.junit.Assert.assertTrue;
+
+public class MySQLFormartTest {
+
+    @Getter
+    private static List<String[]> testUnits = new LinkedList();

Review comment:
       final member?

##########
File path: 
shardingsphere-sql-parser/shardingsphere-sql-parser-dialect/shardingsphere-sql-parser-mysql/src/test/java/org/apache/shardingsphere/sql/parser/mysql/MySQLFormartTest.java
##########
@@ -0,0 +1,91 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.shardingsphere.sql.parser.mysql;
+
+import lombok.Getter;
+import org.antlr.v4.runtime.CodePointBuffer;
+import org.antlr.v4.runtime.CodePointCharStream;
+import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.apache.shardingsphere.sql.parser.core.parser.ParseASTNode;
+import org.apache.shardingsphere.sql.parser.mysql.parser.MySQLLexer;
+import org.apache.shardingsphere.sql.parser.mysql.parser.MySQLParser;
+import 
org.apache.shardingsphere.sql.parser.mysql.visitor.format.impl.MySQLDMLFormatSQLVisitor;
+import 
org.apache.shardingsphere.sql.parser.mysql.visitor.format.impl.MySQLFormatSQLVisitor;
+import org.junit.Test;
+
+import java.nio.CharBuffer;
+import java.util.LinkedList;
+import java.util.List;
+
+import static org.junit.Assert.assertTrue;
+
+public class MySQLFormartTest {
+
+    @Getter
+    private static List<String[]> testUnits = new LinkedList();
+
+    {
+        testUnits.add(new String[]{"test", "select a+1 as b, name n from 
table1 join table2 where id=1 and name='lu';", "SELECT a + ? AS b, name n\n"
+                + "FROM table1 JOIN table2\n"
+                + "WHERE \n"
+                + "\tid = ?\n"
+                + "\tandname = ?;"});
+        testUnits.add(new String[]{"", "select id, name, age, sex, ss, yy from 
table1 where id=1", "SELECT id , name , age , \n"
+                + "\tsex , ss , yy \n"
+                + "FROM table1\n"
+                + "WHERE \n"
+                + "\tid = ?;"});
+        testUnits.add(new String[]{"", "select id, name, age, count(*) as n, 
(select id, name, age, sex from table2 where id=2) as sid, yyyy from table1 
where id=1", "SELECT id , name , age , \n"
+                + "\tCOUNT ( * ) AS n, \n"
+                + "\t(\n"
+                + "\t\tSELECT id , name , age , \n"
+                + "\t\t\tsex \n"
+                + "\t\tFROM table2\n"
+                + "\t\tWHERE \n"
+                + "\t\t\tid = ?\n"
+                + "\t) AS sid, yyyy \n"
+                + "FROM table1\n"
+                + "WHERE \n"
+                + "\tid = ?;"});
+        testUnits.add(new String[]{"", "select id, name, age, sex, ss, yy from 
table1 where id=1 and name=1 and a=1 and b=2 and c=4 and d=3", "SELECT id , 
name , age , \n"
+                + "\tsex , ss , yy \n"
+                + "FROM table1\n"
+                + "WHERE \n"
+                + "\tid = ?\n"
+                + "\tandname = ?\n"
+                + "\tanda = ?\n"
+                + "\tandb = ?\n"
+                + "\tandc = ?\n"
+                + "\tandd = ?;"});
+        testUnits.add(new String[]{"", "ALTER TABLE t_log ADD name 
varchar(10)", "ALTER TABLE t_log ADD name VARCHAR ( 10 )"});
+    }
+
+    @Test
+    public final void assertTest() {
+        for (String[] each : testUnits) {
+            CodePointBuffer buffer = 
CodePointBuffer.withChars(CharBuffer.wrap(each[1].toCharArray()));
+            MySQLLexer lexer = new 
MySQLLexer(CodePointCharStream.fromBuffer(buffer));
+            MySQLParser parser = new MySQLParser(new CommonTokenStream(lexer));
+            ParseTree tree = ((ParseASTNode) parser.parse()).getRootNode();
+            MySQLFormatSQLVisitor visitor = new MySQLDMLFormatSQLVisitor();
+            String result = visitor.visit(tree);
+            assertTrue("SQL format error", each[2].equals(result));

Review comment:
       So this test...just intends to get an error assertion result? How about 
getting a standard and correct assertion?

##########
File path: 
shardingsphere-sql-parser/shardingsphere-sql-parser-dialect/shardingsphere-sql-parser-mysql/src/main/java/org/apache/shardingsphere/sql/parser/mysql/visitor/format/impl/MySQLFormatSQLVisitor.java
##########
@@ -19,11 +19,423 @@
 
 import lombok.AccessLevel;
 import lombok.Getter;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.antlr.v4.runtime.tree.RuleNode;
+import org.antlr.v4.runtime.tree.TerminalNode;
 import org.apache.shardingsphere.sql.parser.autogen.MySQLStatementBaseVisitor;
+import org.apache.shardingsphere.sql.parser.autogen.MySQLStatementParser;
 
 /**
  * MySQL Format SQL visitor for MySQL.
  */
 @Getter(AccessLevel.PROTECTED)
 public abstract class MySQLFormatSQLVisitor extends 
MySQLStatementBaseVisitor<String> {
+    private StringBuilder result = new StringBuilder();

Review comment:
       A blank line is needed above. Besides, why do we not use the result 
returned by each `visitXXX()` immediately (Currently, those returned results 
seem unused)?  That way, we could keep the same way as `StatementVisitors`.  

##########
File path: 
shardingsphere-sql-parser/shardingsphere-sql-parser-dialect/shardingsphere-sql-parser-mysql/src/test/java/org/apache/shardingsphere/sql/parser/mysql/MySQLFormartTest.java
##########
@@ -0,0 +1,91 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.shardingsphere.sql.parser.mysql;
+
+import lombok.Getter;
+import org.antlr.v4.runtime.CodePointBuffer;
+import org.antlr.v4.runtime.CodePointCharStream;
+import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.apache.shardingsphere.sql.parser.core.parser.ParseASTNode;
+import org.apache.shardingsphere.sql.parser.mysql.parser.MySQLLexer;
+import org.apache.shardingsphere.sql.parser.mysql.parser.MySQLParser;
+import 
org.apache.shardingsphere.sql.parser.mysql.visitor.format.impl.MySQLDMLFormatSQLVisitor;
+import 
org.apache.shardingsphere.sql.parser.mysql.visitor.format.impl.MySQLFormatSQLVisitor;
+import org.junit.Test;
+
+import java.nio.CharBuffer;
+import java.util.LinkedList;
+import java.util.List;
+
+import static org.junit.Assert.assertTrue;
+
+public class MySQLFormartTest {
+
+    @Getter
+    private static List<String[]> testUnits = new LinkedList();
+
+    {
+        testUnits.add(new String[]{"test", "select a+1 as b, name n from 
table1 join table2 where id=1 and name='lu';", "SELECT a + ? AS b, name n\n"
+                + "FROM table1 JOIN table2\n"
+                + "WHERE \n"
+                + "\tid = ?\n"
+                + "\tandname = ?;"});
+        testUnits.add(new String[]{"", "select id, name, age, sex, ss, yy from 
table1 where id=1", "SELECT id , name , age , \n"
+                + "\tsex , ss , yy \n"
+                + "FROM table1\n"
+                + "WHERE \n"
+                + "\tid = ?;"});
+        testUnits.add(new String[]{"", "select id, name, age, count(*) as n, 
(select id, name, age, sex from table2 where id=2) as sid, yyyy from table1 
where id=1", "SELECT id , name , age , \n"
+                + "\tCOUNT ( * ) AS n, \n"
+                + "\t(\n"
+                + "\t\tSELECT id , name , age , \n"
+                + "\t\t\tsex \n"
+                + "\t\tFROM table2\n"
+                + "\t\tWHERE \n"
+                + "\t\t\tid = ?\n"
+                + "\t) AS sid, yyyy \n"
+                + "FROM table1\n"
+                + "WHERE \n"
+                + "\tid = ?;"});
+        testUnits.add(new String[]{"", "select id, name, age, sex, ss, yy from 
table1 where id=1 and name=1 and a=1 and b=2 and c=4 and d=3", "SELECT id , 
name , age , \n"
+                + "\tsex , ss , yy \n"
+                + "FROM table1\n"
+                + "WHERE \n"
+                + "\tid = ?\n"
+                + "\tandname = ?\n"
+                + "\tanda = ?\n"
+                + "\tandb = ?\n"
+                + "\tandc = ?\n"
+                + "\tandd = ?;"});
+        testUnits.add(new String[]{"", "ALTER TABLE t_log ADD name 
varchar(10)", "ALTER TABLE t_log ADD name VARCHAR ( 10 )"});
+    }
+
+    @Test
+    public final void assertTest() {

Review comment:
       This name seems to be vague for this test assertion

##########
File path: 
shardingsphere-sql-parser/shardingsphere-sql-parser-dialect/shardingsphere-sql-parser-mysql/src/test/java/org/apache/shardingsphere/sql/parser/mysql/MySQLFormartTest.java
##########
@@ -0,0 +1,91 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.shardingsphere.sql.parser.mysql;
+
+import lombok.Getter;
+import org.antlr.v4.runtime.CodePointBuffer;
+import org.antlr.v4.runtime.CodePointCharStream;
+import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.apache.shardingsphere.sql.parser.core.parser.ParseASTNode;
+import org.apache.shardingsphere.sql.parser.mysql.parser.MySQLLexer;
+import org.apache.shardingsphere.sql.parser.mysql.parser.MySQLParser;
+import 
org.apache.shardingsphere.sql.parser.mysql.visitor.format.impl.MySQLDMLFormatSQLVisitor;
+import 
org.apache.shardingsphere.sql.parser.mysql.visitor.format.impl.MySQLFormatSQLVisitor;
+import org.junit.Test;
+
+import java.nio.CharBuffer;
+import java.util.LinkedList;
+import java.util.List;
+
+import static org.junit.Assert.assertTrue;
+
+public class MySQLFormartTest {

Review comment:
       Please make it  ` final` unless it has any child classes.

##########
File path: 
shardingsphere-sql-parser/shardingsphere-sql-parser-dialect/shardingsphere-sql-parser-mysql/src/main/java/org/apache/shardingsphere/sql/parser/mysql/visitor/format/impl/MySQLFormatSQLVisitor.java
##########
@@ -19,11 +19,423 @@
 
 import lombok.AccessLevel;
 import lombok.Getter;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.antlr.v4.runtime.tree.RuleNode;
+import org.antlr.v4.runtime.tree.TerminalNode;
 import org.apache.shardingsphere.sql.parser.autogen.MySQLStatementBaseVisitor;
+import org.apache.shardingsphere.sql.parser.autogen.MySQLStatementParser;
 
 /**
  * MySQL Format SQL visitor for MySQL.
  */
 @Getter(AccessLevel.PROTECTED)
 public abstract class MySQLFormatSQLVisitor extends 
MySQLStatementBaseVisitor<String> {
+    private StringBuilder result = new StringBuilder();
+
+    private final boolean uperCase = true;
+
+    private int indentCount;
+
+    private int lines;
+
+    private int projectionsCountOfLine = 3;
+
+    @Override
+    public String visitSelect(final MySQLStatementParser.SelectContext ctx) {
+        if (null != ctx.queryExpression()) {
+            visit(ctx.queryExpression());
+            if (null != ctx.lockClauseList()) {
+                result.append(" ");
+                visit(ctx.lockClauseList());
+            }
+        } else if (null != ctx.queryExpressionParens()) {
+            visit(ctx.queryExpressionParens());
+        } else {
+            visit(ctx.selectWithInto());
+        }
+        print(";");
+        return result.toString();
+    }
+
+    @Override
+    public String visitQueryExpression(final 
MySQLStatementParser.QueryExpressionContext ctx) {
+        if (null != ctx.withClause()) {
+            visit(ctx.withClause());
+            print(" ");
+        }
+        if (null != ctx.queryExpressionBody()) {
+            visit(ctx.queryExpressionBody());
+        } else {
+            visit(ctx.queryExpressionParens());
+        }
+        if (null != ctx.orderByClause()) {
+            print(" ");
+            visit(ctx.orderByClause());
+        }
+        if (null != ctx.limitClause()) {
+            print(" ");
+            visit(ctx.limitClause());
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitQueryExpressionParens(final 
MySQLStatementParser.QueryExpressionParensContext ctx) {
+        println();
+        this.indentCount++;
+        print("(");
+        println();
+        if (null != ctx.queryExpressionParens()) {
+            visit(ctx.queryExpressionParens());
+        } else {
+            visit(ctx.queryExpression());
+            if (null != ctx.lockClauseList()) {
+                result.append(" ");
+                visit(ctx.lockClauseList());
+            }
+        }
+        this.indentCount--;
+        println();
+        print(")");
+        return result.toString();
+    }
+
+    @Override
+    public String visitQueryExpressionBody(final 
MySQLStatementParser.QueryExpressionBodyContext ctx) {
+        if (1 == ctx.getChildCount()) {
+            visit(ctx.queryPrimary());
+        } else {
+            visit(ctx.queryExpressionParens(0));
+            result.append("\nUNION\n");
+            if (null != ctx.unionOption()) {
+                visit(ctx.unionOption());
+                result.append(" ");
+            }
+            if (null != ctx.queryPrimary()) {
+                visit(ctx.queryPrimary());
+            } else {
+                visit(ctx.queryExpressionParens(1));
+            }
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitQuerySpecification(final 
MySQLStatementParser.QuerySpecificationContext ctx) {
+        print("SELECT ");
+        int selectSpecCount = ctx.selectSpecification().size();
+        for (int i = 0; i < selectSpecCount; i++) {
+            visit(ctx.selectSpecification(i));
+            print(" ");
+        }
+        visit(ctx.projections());
+        if (null != ctx.fromClause()) {
+            println();
+            visit(ctx.fromClause());
+        }
+        if (null != ctx.whereClause()) {
+            println();
+            visit(ctx.whereClause());
+        }
+        if (null != ctx.groupByClause()) {
+            println();
+            visit(ctx.groupByClause());
+        }
+        if (null != ctx.havingClause()) {
+            println();
+            visit(ctx.havingClause());
+        }
+        if (null != ctx.windowClause()) {
+            println();
+            visit(ctx.windowClause());
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitExplicitTable(final 
MySQLStatementParser.ExplicitTableContext ctx) {
+        print("TABLE ");
+        visit(ctx.tableName());
+        return result.toString();
+    }
+
+    @Override
+    public String visitTableName(final MySQLStatementParser.TableNameContext 
ctx) {
+        if (null != ctx.owner()) {
+            print(ctx.owner().getText());
+            print(".");
+        }
+        print(ctx.name().getText());
+        return result.toString();
+    }
+
+    @Override
+    public String visitTableValueConstructor(final 
MySQLStatementParser.TableValueConstructorContext ctx) {
+        print("VALUES ");
+        visit(ctx.rowConstructorList());
+        return result.toString();
+    }
+
+    @Override
+    public String visitRowConstructorList(final 
MySQLStatementParser.RowConstructorListContext ctx) {
+        int rowCount = ctx.assignmentValues().size();
+        for (int i = 0; i < rowCount; i++) {
+            if (i != 0 && i != rowCount) {
+                print(", ROW");
+                visit(ctx.assignmentValues(i));
+
+            } else {
+                print("ROW");
+                visit(ctx.assignmentValues(i));
+            }
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitAssignmentValues(final 
MySQLStatementParser.AssignmentValuesContext ctx) {
+        print("(");
+        int assignCount = ctx.assignmentValue().size();
+        for (int i = 0; i < assignCount; i++) {
+            if (i != 0) {
+                print(", ");
+                visit(ctx.assignmentValue(i));
+            } else {
+                visit(ctx.assignmentValue(i));
+            }
+        }
+        print(")");
+        return result.toString();
+    }
+
+    @Override
+    public String visitWhereClause(final 
MySQLStatementParser.WhereClauseContext ctx) {
+        visit(ctx.WHERE());
+        print(" ");
+        this.indentCount++;
+        println();
+        visit(ctx.expr());
+        this.indentCount--;
+        return result.toString();
+    }
+
+    @Override
+    public String visitExpr(final MySQLStatementParser.ExprContext ctx) {
+        if (null != ctx.logicalOperator()) {
+            MySQLStatementParser.ExprContext left = ctx.expr(0);
+            visit(left);
+            println();
+            MySQLStatementParser.ExprContext right = ctx.expr(1);
+            print(ctx.logicalOperator().getText());
+            visit(right);
+        } else if (null != ctx.notOperator()) {
+            print(ctx.notOperator().getText());
+            visit(ctx.expr(0));
+        } else {
+            visitChildren(ctx);
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitAlias(final MySQLStatementParser.AliasContext ctx) {
+        print(ctx.getText());
+        return result.toString();
+    }
+
+    @Override
+    public String visitProjections(final 
MySQLStatementParser.ProjectionsContext ctx) {
+        this.indentCount++;
+        if (null != ctx.unqualifiedShorthand()) {
+            visit(ctx.unqualifiedShorthand());
+            result.append(" ");
+        }
+        int projectionCount = ctx.projection().size();
+        int lineItemCount = 0;
+        for (int i = 0; i < projectionCount; i++) {
+            if (0 != i) {
+                result.append(", ");
+                if (lineItemCount >= projectionsCountOfLine) {
+                    lineItemCount = 0;
+                    println();
+                }
+            }
+            visit(ctx.projection(i));
+            lineItemCount++;
+        }
+        this.indentCount--;
+        return result.toString();
+    }
+
+    @Override
+    public String visitProjection(final MySQLStatementParser.ProjectionContext 
ctx) {
+        if (null != ctx.expr()) {
+            visit(ctx.expr());
+            print(" ");
+        }
+        if (null != ctx.AS()) {
+            print("AS ");
+        }
+        if (null != ctx.alias()) {
+            visit(ctx.alias());
+        }
+        if (null != ctx.qualifiedShorthand()) {
+            visit(ctx.qualifiedShorthand());
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitTerminal(final TerminalNode node) {
+        if (isUperCase()) {
+            print(node.getText().toUpperCase());
+        } else {
+            print(node.getText().toLowerCase());
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitIdentifier(final MySQLStatementParser.IdentifierContext 
ctx) {
+        print(ctx.getText());
+        return result.toString();
+    }
+
+    @Override
+    public String visitLiterals(final MySQLStatementParser.LiteralsContext 
ctx) {
+        print("?");
+        return result.toString();
+    }
+
+    @Override
+    public String visitStringLiterals(final 
MySQLStatementParser.StringLiteralsContext ctx) {
+        print("?");
+        return result.toString();
+    }
+
+    @Override
+    public String visitNumberLiterals(final 
MySQLStatementParser.NumberLiteralsContext ctx) {
+        print("?");
+        return result.toString();
+    }
+
+    @Override
+    public String visitWithClause(final MySQLStatementParser.WithClauseContext 
ctx) {
+        print("WITH ");
+        if (null != ctx.RECURSIVE()) {
+            visit(ctx.RECURSIVE());
+            result.append(" ");
+        }
+        for (int i = 0; i < ctx.cteClause().size(); i++) {
+            if (i != 0 && i < ctx.cteClause().size() - 1) {
+                result.append(", ");
+            }
+            visit(ctx.cteClause(i));
+        }
+        if (null != ctx.parent) {
+            result.append("\n");
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitCteClause(final MySQLStatementParser.CteClauseContext 
ctx) {
+        visit(ctx.ignoredIdentifier());
+        result.append(" ");
+        if (null != ctx.columnNames()) {
+            visit(ctx.columnNames());
+            result.append(" ");
+        }
+        result.append("AS ");
+        visit(ctx.subquery());
+        return result.toString();
+    }
+
+    @Override
+    public String visitIgnoredIdentifier(final 
MySQLStatementParser.IgnoredIdentifierContext ctx) {
+        visit(ctx.identifier(0));
+        if (null != ctx.DOT_()) {
+            visit(ctx.DOT_());
+            visit(ctx.identifier(1));
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitColumnNames(final 
MySQLStatementParser.ColumnNamesContext ctx) {
+        if (null != ctx.LP_()) {
+            visit(ctx.LP_());
+        }
+        int columnCount = ctx.columnName().size();
+        for (int i = 0; i < columnCount; i++) {
+            if (i != 0 && i < columnCount - 1) {
+                result.append(", ");
+            } else {
+                visit(ctx.columnName(i));
+            }
+        }
+        if (null != ctx.RP_()) {
+            visit(ctx.RP_());
+        }
+        return result.toString();
+    }
+
+    @Override
+    public String visitColumnName(final MySQLStatementParser.ColumnNameContext 
ctx) {
+        if (null != ctx.owner()) {
+            visit(ctx.owner());
+            visit(ctx.DOT_(0));
+        }
+        visit(ctx.name());
+        return result.toString();
+    }
+
+    @Override
+    public String visitChildren(final RuleNode node) {
+        String result = defaultResult();
+
+        int n = node.getChildCount();
+        for (int i = 0; i < n; i++) {
+            if (i != 0) {
+                print(" ");
+            }
+            if (!shouldVisitNextChild(node, result)) {
+                break;
+            }
+
+            ParseTree c = node.getChild(i);
+            String childResult = c.accept(this);
+            result = aggregateResult(result, childResult);
+        }
+        return result;
+    }
+
+    private void print(final char value) {
+        if (this.result == null) {

Review comment:
       Given the code standard instruction in doc , `null  == this.result ` is 
preferable, right?




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