SQL details comparison

Null, "" Comparison

Null indicates that no value is assigned, and no value is provided. The data type cannot be determined. It is usually null.

"" Indicates the character type, which is a string of zero length.

 

Char, varchar, and nvarchar comparison

Char occupies a fixed length and space, for example, char (10). If the value is "AB", it also occupies 10 memories, but the last eight positions are "",ProgramTrim () is used for the value, which is more efficient.

Varchar is a variable-length string. varchar (10) is assigned a value of "AB", which occupies two Memory Spaces. It is used for space efficiency, which saves space and sacrifices a little efficiency. Chinese characters occupy two Memory Spaces, byte access

Nvarchar is also variable length. The only difference between nvarchar and varchar is character-based access. Chinese characters occupy one memory space and can store more content than varchar.