What is the average salary of the worst performing managers?
the worst performing refers to performance = 'Poor'; manager is a positiontitle; average salary refers to AVG(salary)
SELECT AVG(CAST(REPLACE(SUBSTR(T1.salary, 4), ',', '') AS REAL)) FROM employee AS T1 INNER JOIN position AS T2  ON T1.positionID = T2.positionID WHERE T1.performance = 'Poor' AND T2.positiontitle = 'Manager'
database name:db_id human_resources
location table location Cols: location id dtype integer, location city dtype text, address dtype text, state dtype text, zip code dtype integer, office phone dtype text, 
position table position Cols: position id dtype integer, position title dtype text, education required dtype text, minimum salary dtype text, maximum salary dtype text, 
employee table employee Cols: social security number dtype text, last name dtype text, first name dtype text, hire date dtype text, salary dtype text, gender dtype text, performance dtype text, position id dtype integer, location id dtype integer, 
