instruction: How many courses each teacher taught? Show me a stacked bar chart. The x-axis is the teacher's first name and group by course description.
response: SELECT EMP_FNAME, COUNT(EMP_FNAME) FROM CLASS AS T1 JOIN EMPLOYEE AS T2 ON T1.PROF_NUM = T2.EMP_NUM JOIN COURSE AS T3 ON T1.CRS_CODE = T3.CRS_CODE GROUP BY CRS_DESCRIPTION, EMP_FNAME