MYSQL: multiple functions in query String

Question

the following query is not working in MYSql (a Trigger)

set new.uniq = SUBSTR(md5(concat(new.lat, '-', new.lon)),0,5)

only if i delete the SUBSTR it will give me an correct output

set new.uniq = md5(concat(new.lat, '-', new.lon))

Answer 1

The problem is the zero:

set new.uniq = SUBSTR(md5(concat(new.lat, '-', new.lon)),0,5)
                                                         ^

For example:

SELECT SUBSTR('whatever', 0, 5) --> returns empty string
SELECT SUBSTR('whatever', 1, 5) --> returns 'whate'

Change the zero to a 1 and you should be fine:

set new.uniq = SUBSTR(md5(concat(new.lat, '-', new.lon)),1,5)