Basic knowledge of vegetable chicken database

2020.7.12

In the database char and nchar The difference between

char Type is a byte char（8） Can only save 8 Letter nchar The type is double byte nchar（8） Able to survive 8 The Chinese characters

In the database char and varchar The difference between

char The length of the type is fixed ,varchar The length of is variable .

That means , Store string ’abc’, Use char(10), Indicates that the stored characters will account for 10 Bytes （ Include 7 Two empty characters ）

varchar2 Than char Save a space , But it is more efficient than char A little worse . To achieve efficiency, we must sacrifice a little space , This is the design " Space for time "

2020.7.21

SQL Server Point exclamation mark to execute SQL After success , Why doesn't the database content change according to the written code ？

Need to refresh manually , Right click on the database , Right click on the table to find the refresh , And that is , In the blank part of the table , Right click again , perform SQL, That's it , Baidu can't find out how to check this problem , It's so cute