About n before variables in SQL server and other usage analysis

Insert 、 Update data

When there is Chinese in the original data, insert it into SQL server Chinese garbled code will be generated in the database , The solution is ：
The first step is to set the fields that need to store Chinese as nvarchar type

 alter table Test_Info alter column name nvarchar(50)

The second step is to add... Before inserting data N：

insert into Test_Info(name) values(N' cat ')

Note that neither of the two is indispensable , Otherwise, it will lead to the appearance of Chinese garbled code ！
Add N After that, it means that the string is a nvarchar type , Precede string with N You can convert a string to unicode code , Each string is stored in double bytes , In this way, the primary choice of Chinese characters will not be garbled

Inquire about

After completing the previous step, there will be no Chinese garbled code stored , However, when retrieving data, there will still be the phenomenon that Chinese cannot be retrieved . The solution is to add... Before a constant N

-- If not N Will not return correctly name Data for cats select * from Test_Info where name = N' cat '

The variable contains Chinese

More often, we need to query through variables , The variable contains Chinese , So how to SQL stored procedure 、 Add... Before variables of custom functions or scripts N Well ？
The following example uses a stored procedure

create proc test_proc(@name nvarchar(250), @enddateperiod date)asselect * from  Test_Infowhere name=N''[email protected]+''and [date]<= @enddateperiodand [type]<>'Brand'

There are two main parts that are different from the general stored procedure , First, when defining variables, they should be defined as nvarchar type , Two is through N’’+ Variable +’’ Add before the variables of the stored procedure N
Note that neither of the two is indispensable , Otherwise, the query will not produce correct results ！
At the same time, you can ：

create proc test_proc(@name nvarchar(250), @enddateperiod date)asDECLARE @SQL NVARCHAR(100)SET @SQL='select * from  Test_Info where name=N'''[email protected]+''''EXEC (@SQL)

But this method has multiple variables + Writing in the case of character constants is very cumbersome .
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