node.js连接mysql报错Error: Cannot enqueue Handshake after invoking quit.

第一次访问时一切正常不会发生错误，刷新之后就会发生如下错误

Error: Cannot enqueue Handshake after invoking quit.

at Protocol._validateEnqueue (D:\CodeWorkspace\expressmysql\node_modules\mysql\lib\protocol\Protocol.js:215:16)

at Protocol._enqueue (D:\CodeWorkspace\expressmysql\node_modules\mysql\lib\protocol\Protocol.js:138:13)

at Protocol.handshake (D:\CodeWorkspace\expressmysql\node_modules\mysql\lib\protocol\Protocol.js:51:23)

at Connection.connect (D:\CodeWorkspace\expressmysql\node_modules\mysql\lib\Connection.js:119:18)

at D:\CodeWorkspace\expressmysql\src\com\ftg\controller\dept.js:6:8

at Layer.handle [as handle_request] (D:\CodeWorkspace\expressmysql\node_modules\express\lib\router\layer.js:95:5)

at next (D:\CodeWorkspace\expressmysql\node_modules\express\lib\router\route.js:137:13)

at Route.dispatch (D:\CodeWorkspace\expressmysql\node_modules\express\lib\router\route.js:112:3)

at Layer.handle [as handle_request] (D:\CodeWorkspace\expressmysql\node_modules\express\lib\router\layer.js:95:5)

at D:\CodeWorkspace\expressmysql\node_modules\express\lib\router\index.js:281:22

Emitted 'error' event at:

at Connection._handleProtocolError (D:\CodeWorkspace\expressmysql\node_modules\mysql\lib\Connection.js:426:8)

at Protocol.emit (events.js:189:13)

at Protocol._delegateError (D:\CodeWorkspace\expressmysql\node_modules\mysql\lib\protocol\Protocol.js:398:10)

at Handshake.<anonymous> (D:\CodeWorkspace\expressmysql\node_modules\mysql\lib\protocol\Protocol.js:232:10)

at Handshake.emit (events.js:189:13)

at Handshake.Sequence.end (D:\CodeWorkspace\expressmysql\node_modules\mysql\lib\protocol\sequences\Sequence.js:78:12)

at D:\CodeWorkspace\expressmysql\node_modules\mysql\lib\protocol\Protocol.js:236:14

at process._tickCallback (internal/process/next_tick.js:61:11)

连接mysql 然后不断开，一直连着数据库，这样就不会错了，

route_dept.get('/show',function(req,res){

db.connect(); (把这行移动到方法外)

db.query("select * from dept",function (error,results, fields){

if(error) throw error;

var json = {

code:0

,msg:'成功'

,data:results

};

res.send(json); // send end({aa:123})....

db.end(); (删除这行)

});

});