优化SQL语句，加快其执行速度

Question

优化SQL

由于数据量较大，执行下面这条语句需要2s多的时间，请问该如何优化这条语句呢

SELECT COUNT(1)
    num1 
FROM 
    jk_instrument_sports_data d 
WHERE 
    d.equipment_code IN 
    (SELECT e.equipment_code FROM yps_equipment e);

Answer 1

等值查询也是可以的，不过count需要指定值且去重，刚count(1)会出现统计数据不对的情况

SELECT COUNT(DISTINCT d.equipment_code) num1 
FROM jk_instrument_sports_data d, yps_equipment e
WHERE d.equipment_code = e.equipment_code