PostgreSQL?? 'DISTINCT ON ???? ?? ORDER BY ???? ???? ???'? ???? ??? ??????
Jan 21, 2025 pm 12:22 PM
PostgreSQL? DISTINCT ON ?? ?? ?? ? ?? ?? ?? ? ?? ? ??? ??????. ??? DISTINCT ON ???? ?? ORDER BY ???? ???? ?? ? ???? ??? ?????.
DISTINCT ON ?? ??? ??
?? ???? ??:
SELECT DISTINCT ON (address_id) purchases.address_id, purchases.* FROM purchases WHERE purchases.product_id = 1 ORDER BY purchases.purchased_at DESC
??:
<code>PG::Error: ERROR: SELECT DISTINCT ON expressions must match initial ORDER BY expressions</code>
???: DISTINCT ON ? ORDER BY
??
PostgreSQL ????? DISTINCT ON ???? ?? ??? ORDER BY ???? ????? ??? ?????. ???? ?????. ORDER BY ?? ?? ?????.
SELECT DISTINCT ON (address_id) purchases.address_id, purchases.* FROM purchases WHERE purchases.product_id = 1 ORDER BY address_id, purchases.purchased_at DESC
?? ??: address_id??
??
address_id?? ???? ???? ?? ??? ?????.
?? 1: "??? ?? ??? N" ???
? ??? ? ??? ?? ?? ?? ??? ????? ????. address_id:
SELECT t1.*
FROM purchases t1
JOIN (
SELECT address_id, max(purchased_at) as max_purchased_at
FROM purchases
WHERE product_id = 1
GROUP BY address_id
) t2
ON t1.address_id = t2.address_id AND t1.purchased_at = t2.max_purchased_at
ORDER BY t1.purchased_at DESC
?? 2: PostGreSQL? ?? ??
? ?? ??? ?? ??? ???? purchased_at ??? ????? ??? ??? ????.
SELECT * FROM ( SELECT DISTINCT ON (address_id) * FROM purchases WHERE product_id = 1 ORDER BY address_id, purchased_at DESC ) t ORDER BY purchased_at DESC
??? ??? ?? ?? ???? address_id ?? ??? ???? ?? ?? ? ???? ?????. DISTINCT ON ?? ??
? ??? PostgreSQL?? 'DISTINCT ON ???? ?? ORDER BY ???? ???? ???'? ???? ??? ??????? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!
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