mysql行转列

SELECT id,

SUM(CASE `years` WHEN '2019' THEN `mount` ELSE null END) as '2019',
SUM(CASE `years` WHEN '2020' THEN `mount`ELSE null END) as '2020',
SUM(CASE `years` WHEN '2021' THEN `mount` ELSE null END) as '2021'
FROM testdate
GROUP BY id