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How to optimize this SQL?

2022-07-22 15:14:00 【CSDN Q & A】

SELECT
s.id AS schoolId,
#{param.billNumber} as bill_number,
sum( CASE WHEN t.category = 1 THEN 1 ELSE 0 END ) AS a
sum( CASE WHEN t.category = 2 THEN 1 ELSE 0 END ) AS b,
sum( CASE WHEN t.category = 3 THEN 1 ELSE 0 END ) AS c,
s.short_name AS schoolName,
s.city
FROM
school s
LEFT JOIN classhour_student t ON t.school_id = s.id
AND t.delete_flag = 0
AND t.created_time >= "2022-06-01 00:00:00"
AND t.created_time <= "2022-06-30 23:59:59"
WHERE
s.type = 1
What can be optimized ？