我在join語句中使用子查詢組合了乙個相當簡單的查詢.它僅在我在子查詢select中包含*時才有效.為什麼？
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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