diff --git a/src/sqlParser.jison b/src/sqlParser.jison
index 40b0631..f322390 100644
--- a/src/sqlParser.jison
+++ b/src/sqlParser.jison
@@ -89,6 +89,7 @@ SHARE                                                             return 'SHARE'
 MODE                                                              return 'MODE'
 OJ                                                                return 'OJ'
 LIMIT                                                             return 'LIMIT'
+UNION                                                             return 'UNION'
 
 ","                                                               return ','
 "="                                                               return '='
@@ -159,8 +160,32 @@ LIMIT                                                             return 'LIMIT'
 %% /* language grammar */
 
 main
-  : selectClause EOF { return {nodeType: 'Main', value: $1}; }
-  | selectClause ';' EOF { return {nodeType: 'Main', value: $1, hasSemicolon: true}; }
+  : selectClause semicolonOpt EOF { return {nodeType: 'Main', value: $1, hasSemicolon: $2}; }
+  | unionClause semicolonOpt EOF { return {nodeType: 'Main', value: $1, hasSemicolon: $2}; }
+  ;
+
+semicolonOpt
+  : ';' { $$ = true }
+  | { $$ = false }
+  ;
+
+unionClause
+  : unionClauseNotParenthesized { $$ = $1 }
+  | unionClauseParenthesized order_by_opt limit_opt { $$ = $1, $$.orderBy = $2, $$.limit = $3; }
+  ;
+
+unionClauseParenthesized
+  : selectClauseParenthesized UNION distinctOpt selectClauseParenthesized { $$ = { type: 'Union', left: $1, distinctOpt: $3, right: $4 }; }
+  | selectClauseParenthesized UNION distinctOpt unionClauseParenthesized { $$ = { type: 'Union', left: $1, distinctOpt: $3, right: $4 }; }
+  ;
+
+selectClauseParenthesized
+  : '(' selectClause ')' { $$ = { type: 'SelectParenthesized', value: $2 }; }
+  ;
+
+unionClauseNotParenthesized
+  : selectClause UNION distinctOpt selectClause { $$ = { type: 'Union', left: $1, distinctOpt: $3, right: $4 } }
+  | selectClause UNION distinctOpt unionClauseNotParenthesized { $$ = { type: 'Union', left: $1, distinctOpt: $3, right: $4 } }
   ;
 
 selectClause
diff --git a/src/stringify.js b/src/stringify.js
index fd1d289..338479e 100644
--- a/src/stringify.js
+++ b/src/stringify.js
@@ -1,3 +1,5 @@
+import { timingSafeEqual } from "crypto";
+
 if (!sqlParser) {
   sqlParser = {};
 }
@@ -55,13 +57,13 @@ Sql.prototype.append = function(word, noPrefix, noSuffix) {
   }
 }
 Sql.prototype.travelMain = function(ast) {
-  this.travelSelect(ast.value);
+  this.travel(ast.value);
   if (ast.hasSemicolon) {
     this.append(';', true);
   }
 }
 Sql.prototype.travelSelect = function(ast) {
-  this.appendKeyword('select', true);
+  this.appendKeyword('select');
   if (ast.distinctOpt) {
     this.appendKeyword(ast.distinctOpt);
   }
@@ -537,3 +539,16 @@ Sql.prototype.travelTableFactor = function (ast) {
     this.travel(ast.indexHintOpt);
   }
 }
+Sql.prototype.travelUnion = function (ast) {
+  this.travel(ast.left);
+  this.appendKeyword('UNION');
+  if (ast.distinctOpt) {
+    this.appendKeyword(ast.distinctOpt)
+  }
+  this.travel(ast.right);
+}
+Sql.prototype.travelSelectParenthesized = function (ast) {
+  this.appendKeyword('(');
+  this.travel(ast.value);
+  this.appendKeyword(')');
+}
diff --git a/test/main.test.js b/test/main.test.js
index b4114ba..8908c22 100644
--- a/test/main.test.js
+++ b/test/main.test.js
@@ -5,9 +5,13 @@ const parser = require('../');
 
 const testParser = function (sql) {
   let firstAst = parser.parse(sql);
+  debug(JSON.stringify(firstAst, null, 2));
   let firstSql = parser.stringify(firstAst);
+  debug(firstSql);
   let secondAst = parser.parse(firstSql);
+  debug(parser.stringify(secondAst));
   let secondSql = parser.stringify(secondAst);
+  debug(JSON.stringify(secondAst, null, 2));
 
   if (firstSql !== secondSql) {
     console.log('firstSql', firstSql);
@@ -15,9 +19,6 @@ const testParser = function (sql) {
     throw 'err firstSql don\'t equals secondSql. ';
   }
 
-  debug(JSON.stringify(secondAst, null, 2));
-  debug(parser.stringify(secondAst));
-
   return secondAst;
 }
 
@@ -360,5 +361,21 @@ describe('select grammar support', function () {
     testParser('SELECT COUNT(*) AS total, a b, b as c, c/2 d, d & e an FROM b');
   });
 
+  it ('union support, https://dev.mysql.com/doc/refman/8.0/en/union.html', function () {
+    testParser('select a from dual union select a from foo;');
+  });
+
+  it ('union Parenthesized support, https://dev.mysql.com/doc/refman/8.0/en/union.html', function () {
+    testParser('(select a from dual) union (select a from foo) order by a desc limit 100, 100;');
+  });
+
+  it ('union all support, https://dev.mysql.com/doc/refman/8.0/en/union.html', function () {
+    testParser('(select a from dual) union all (select a from foo) order by a limit 100');
+  });
+
+  it ('union distinct support, https://dev.mysql.com/doc/refman/8.0/en/union.html', function () {
+    testParser('select a from dual order by a desc limit 1, 1 union distinct select a from foo order by a limit 1');
+  });
+
 });