How to convert "" to null?

Question

For example, a="", how to convert it into a=null, which is used to transfer values ​​​​through the interface. "" cannot be used, only null can be used, but the value of the option object without value obtained by using select is "", please tell me How to solve?

Answer 1

var a='';
//传之前
a=a||null;

Answer 2

a===""&&(a=null)

Answer 3

var a="";
a=a===""?null:a;

Answer 4

a===""&&(a=null)

Answer 5

Use select(CASE WHEN(a = '') THEN null ELSE a END) AS a from...This way, you can refer to the article http://blog.csdn.net/qq_16990...