enhance sql parser & add test

src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlLexer.java

@@ -112,6 +112,7 @@ public class MySqlLexer extends Lexer {
         map.put("KILL", Token.KILL);
         map.put("IDENTIFIED", Token.IDENTIFIED);
         map.put("PASSWORD", Token.PASSWORD);
+        map.put("DUAL", Token.DUAL);
 
         DEFAULT_MYSQL_KEYWORDS = new Keywords(map);
     }

src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlStatementParser.java

@@ -768,7 +768,7 @@ public class MySqlStatementParser extends SQLStatementParser {
 
         if (identifierEquals("ROWS")) {
             lexer.nextToken();
-            acceptIdentifier("IDENTIFIED");
+            accept(Token.IDENTIFIED);
             accept(Token.BY);
             SQLExpr rowsIdentifiedBy = exprParser.expr();
             stmt.setRowsIdentifiedBy(rowsIdentifiedBy);

src/main/java/com/alibaba/druid/sql/dialect/mysql/visitor/MySqlSchemaStatVisitor.java

@@ -5,6 +5,7 @@ import java.util.Map;
 
 import com.alibaba.druid.sql.ast.SQLName;
 import com.alibaba.druid.sql.ast.expr.SQLIdentifierExpr;
+import com.alibaba.druid.sql.ast.statement.SQLSelectStatement;
 import com.alibaba.druid.sql.dialect.mysql.ast.MySqlKey;
 import com.alibaba.druid.sql.dialect.mysql.ast.MySqlPrimaryKey;
 import com.alibaba.druid.sql.dialect.mysql.ast.expr.MySqlBinaryExpr;
@@ -43,6 +44,13 @@ import com.alibaba.druid.stat.TableStat.Mode;
 
 public class MySqlSchemaStatVisitor extends SchemaStatVisitor implements MySqlASTVisitor {
 
+    public boolean visit(SQLSelectStatement x) {
+        aliasLocal.set(new HashMap<String, String>());
+        aliasLocal.get().put("DUAL", null);
+        
+        return true;
+    }
+    //DUAL
     public boolean visit(MySqlDeleteStatement x) {
         aliasLocal.set(new HashMap<String, String>());
 

src/main/java/com/alibaba/druid/sql/dialect/postgresql/ast/stmt/PGSelectStatement.java

@@ -1,5 +1,6 @@
 package com.alibaba.druid.sql.dialect.postgresql.ast.stmt;
 
+import com.alibaba.druid.sql.ast.statement.SQLSelect;
 import com.alibaba.druid.sql.ast.statement.SQLSelectStatement;
 import com.alibaba.druid.sql.dialect.postgresql.ast.PGWithClause;
 import com.alibaba.druid.sql.dialect.postgresql.visitor.PGASTVisitor;
@@ -10,6 +11,13 @@ public class PGSelectStatement extends SQLSelectStatement implements PGSQLStatem
     private static final long serialVersionUID = 1L;
     private PGWithClause      with;
 
+    public PGSelectStatement(){
+    }
+
+    public PGSelectStatement(SQLSelect select){
+        super(select);
+    }
+
     public PGWithClause getWith() {
         return with;
     }
@@ -17,7 +25,7 @@ public class PGSelectStatement extends SQLSelectStatement implements PGSQLStatem
     public void setWith(PGWithClause with) {
         this.with = with;
     }
-    
+
     protected void accept0(SQLASTVisitor visitor) {
         accept0((PGASTVisitor) visitor);
     }

src/main/java/com/alibaba/druid/sql/dialect/postgresql/parser/PGSQLStatementParser.java

@@ -15,6 +15,7 @@ import com.alibaba.druid.sql.dialect.postgresql.ast.PGWithClause;
 import com.alibaba.druid.sql.dialect.postgresql.ast.PGWithQuery;
 import com.alibaba.druid.sql.dialect.postgresql.ast.stmt.PGDeleteStatement;
 import com.alibaba.druid.sql.dialect.postgresql.ast.stmt.PGInsertStatement;
+import com.alibaba.druid.sql.dialect.postgresql.ast.stmt.PGSelectStatement;
 import com.alibaba.druid.sql.dialect.postgresql.ast.stmt.PGTruncateStatement;
 import com.alibaba.druid.sql.dialect.postgresql.ast.stmt.PGUpdateStatement;
 import com.alibaba.druid.sql.parser.Lexer;
@@ -311,6 +312,10 @@ public class PGSQLStatementParser extends SQLStatementParser {
         return withQuery;
     }
     
+    public PGSelectStatement parseSelect() throws ParserException {
+        return new PGSelectStatement(createSQLSelectParser().select());
+    }
+    
     public SQLStatement parseWith() {
         PGWithClause with = this.parseWithClause();
         if (lexer.token() == Token.INSERT) {
@@ -318,7 +323,12 @@ public class PGSQLStatementParser extends SQLStatementParser {
             stmt.setWith(with);
             return stmt;
         }
-        
+
+        if (lexer.token() == Token.SELECT) {
+            PGSelectStatement stmt = this.parseSelect();
+            stmt.setWith(with);
+            return stmt;
+        }
         throw new ParserException("TODO");
     }
 }

src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java

@@ -198,6 +198,12 @@ public class SQLExprParser extends SQLParser {
                 sqlExpr = new SQLDefaultExpr();
                 lexer.nextToken();
                 break;
+            case USER:
+            case PASSWORD:
+            case DUAL:
+                sqlExpr = new SQLIdentifierExpr(lexer.stringVal());
+                lexer.nextToken();
+                break;
             case CASE:
                 SQLCaseExpr caseExpr = new SQLCaseExpr();
                 lexer.nextToken();

src/main/java/com/alibaba/druid/sql/parser/Token.java

@@ -102,6 +102,7 @@ public enum Token {
     KILL("KILL"),
     IDENTIFIED("IDENTIFIED"),
     PASSWORD("PASSWORD"),
+    DUAL("DUAL"),
     
     //postgresql
     WINDOW("WINDOW"),