Mysql two ways to update some of the data in a field _mysql

MySQL update some of the data in the field in the first case:

Copy Code code as follows:

Update tab SET A = concat (substring (a,1,3), ' BBB ');

Starting with the 1 characters of a, 3 characters, plus ' BBB ', and writing to a, if a original value is ' 123aaa ', then ' 123BBB ' after the update.

What if we were to replace 1 of the included in the value of a field a with 2?
For example: a=2211, now to replace 2222, is to replace 1 to 2
The SQL statement writes this:

Copy Code code as follows:

Update table Set A=replace (A, ' 1 ', ' 2 ');