create table test(name varchar(5));
insert into test values('bai'),('bai ');
mysql> select length(name) from test;
+--------------+
| length(name) |
+--------------+
|            3 |
|            4 |
+--------------+
2 rows in set (0.00 sec)

mysql> select concat("'",name,"'") from test;
+----------------------+
 

| concat("'",name,"'") |
+----------------------+
| 'bai'                |
| 'bai '               |
+----------------------+

mysql> create table test2(name char(5));
Query OK, 0 rows affected (0.02 sec)

mysql> insert into test2 values('bai'),('bai ');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select concat("'",name,"'") from test2;
+----------------------+
 

| concat("'",name,"'") |
+----------------------+
| 'bai'                |
| 'bai'                |
+----------------------+
2 rows in set (0.00 sec)

看到varchar會保留後面的空格，char會刪掉空格