我在JOIN語句中使用子查詢組合了一個相當簡單的查詢.它僅在我在子查詢select中包含*時才有效.為什么？

這很有效

$sql = 'SELECT locations.id, title, name, hours.lobby

FROM locations

LEFT JOIN states ON states.id = locations.state_id

LEFT JOIN (SELECT *, type_id IS NOT NULL AS lobby FROM location_hours) AS hours ON locations.id = hours.location_id

GROUP BY locations.id';

這沒有

$sql = 'SELECT locations.id, title, name, hours.lobby

FROM locations

LEFT JOIN states ON states.id = locations.state_id

LEFT JOIN (SELECT type_id IS NOT NULL AS lobby FROM location_hours) AS hours ON locations.id = hours.location_id

GROUP BY locations.id';

我應該這樣做嗎？如果你不需要所有的領域,我認為*不是最好的？

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