[ask] count items in the SET(value1,value2,value3)

[Morning Star]

Hi guys,
i created a table, one of column named categories contain SET as its
data type. let's say there are N-value in that column.
i inserted a row to that column which contain only 5 values.
INSERT INTO table SET categories ='value1, value2, value3, value4, value5' ;
the question is: how can i count that items ( value1 till value5) ?

Greetings,

Marco