Not sure, but it seems like an empty string is stored. You can have a piece of data with a null value, and then check the type of the null field value. If it is string, it is an empty string, if not, it is null. To put it simply, var testString = ""; //This declares a testString string, equal to "", which is already stored in memory. var testString = null; //This declares a testString variable, which is just a variable and does not actually allocate memory space. If you don’t understand, just think about it this way. If you use a writing word to represent this process, "" means a blank piece of paper with no writing on it. And null means you don't even have a blank piece of paper.
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Empty strings are OK, try not to use null. This is a keyword, which will be a pitfall in your future index optimization
Not sure, but it seems like an empty string is stored. You can have a piece of data with a null value, and then check the type of the null field value. If it is string, it is an empty string, if not, it is null.
To put it simply,
var testString = ""; //This declares a testString string, equal to "", which is already stored in memory.
var testString = null; //This declares a testString variable, which is just a variable and does not actually allocate memory space.
If you don’t understand, just think about it this way. If you use a writing word to represent this process, "" means a blank piece of paper with no writing on it. And null means you don't even have a blank piece of paper.
not null default ""