lpad,substring and etc

[Anon]

I am going to update a table and update the the data.

for example:

table1:
memberid char(8)
name char(20)

memberid
MT100001
MT100002
MT100003
...
MT100200

I would like to update table1 where memberid with "MT" to "JK", so how to write the query in Mysql, eg. substr(1,2)='JK', so how about in mysql, what are the command ?

thank you.