Force the PATH in your script, cron may not provides the same path as the one you have in a terminal session.
EDIT:
In a terminal get your PATH:
env | grep "^PATH="
PATH=/sbin:/usr/sbin:/usr/local/sbin:... (you will have different value
Cut and paste that line in your script just bellow the #!/bin/bash
#!/bin/bash
PATH=/sbin:/usr/sbin:/usr/local/sbin: (put your path
export PATH
(thats just for instance)
There may be other variable to add in your script; look for variable which names contain the 'MYSQL' string with env | grep MYSQL and set | grep MYSQL