In. Net strange SQL query statements

When I write an SQL query statement in a program recently

I found a strange problem:

Select * Form tablename where name = '"+ textbox1.text + "'"

Sometimes, there is no problem in running.

However, sometimes problems occur.

For example, the content of textbox1.text is AAA

By program, all records meeting name = aaa should be queried.

(Here I want to declare that the database absolutely has a name = aaa record)

However, unexpectedly, after the program runs

No result is displayed (meaning no result is found)

At that time, I was dizzy.

Later, I rummaged over some materials. I had to do this:

Select * Form tablename where name = N' "+ textbox1.text + "'"

The program can get the desired results no matter how it runs!

[In fact, although the requirements have been met, I still don't understand why "N" must be added.]

I wanted to send my post to my experience zone, but I thought about it later.

Maybe someone in the same industry has encountered a cainiao-level problem like me.

It is hard to understand theoretically

So let's use it on the homepage. Maybe someone else can give me some advice!

Dudu, sorry.