選擇行如何在SQL

查詢我有一個用例類似選擇行如何在SQL

a 3 
a 4 
a 5 
a 6 
a 5 
b 3 
b 5 
b 3

如何得到這樣

a 4 
a 5 
b 5 
b 3

輸出選擇a和b的HIGHT數量，但只有2行

這就是我現在寫的查詢，似乎它不工作

SELECT id, barcode, actualsku, inventorycount 
FROM ( SELECT pallet.id        AS id, 
      pallet.barcode      AS barcode,  
      inventoryunit.sku      AS actualsku, 
      Count(inventoryunit.id)    AS inventorycount 
    FROM (SELECT * 
     FROM mft.asset 
     WHERE container_type = 'PALLET' 
       AND location_type = 'PRIME' :: mft.location_type 
       AND is_deleted = FALSE 
       AND (attributes ->> 'sku' :: text) IS NOT NULL) pallet 
      LEFT OUTER JOIN (SELECT * 
       FROM mft.asset 
       WHERE asset_type = 'INVENTORYUNIT' :: mft.asset_type 
         AND is_deleted = FALSE) inventoryunit 
       ON pallet.id = inventoryunit.parent_id 
    GROUP BY inventoryunit.sku, 
      pallet.id, 
      pallet.barcode, 
      pallet.attributes) test 
WHERE (SELECT COUNT(*) FROM test as t 
    WHERE t.actualsku = test.actualsku 
     AND t.inventorycount <= test.inventorycount 
     ) <= 2

來源

2017-03-24 ni yanwen

你如何選擇兩行？ –

結果背後的邏輯是什麼？ – maSTAShuFu

這是一個重複的http://stackoverflow.com/questions/15969614/in-sql-how-to-select-the-top-2-rows-for-each-group – jakewins

個

這通常是利用窗口函數：

select col1, col2 
from (
    select col1, col2, 
     row_number() over (partition by col1 order by col2 desc) as rnk 
    from the_table 
) t 
where rnk <= 2 
order by col1, col2;

在線例如：http://rextester.com/WKLTSB43296

來源

2017-03-25 11:36:43

選擇行如何在SQL

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