Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_204_11 ( id number, "year" number, "fbs opponent" text, "result" text, "opponent's conference" text, "opponent's head coach" text, "charleston southern's head coach" text )

### Question ###
who was the longest head coach ?

### Accurate SQL ###

SELECT "charleston southern's head coach" FROM table_204_11 GROUP BY "charleston southern's head coach" ORDER BY COUNT(*) DESC LIMIT 1