選擇加入SQL查詢計數

如何使用查詢分別查看a，b，c，d添加的產品數量？選擇加入SQL查詢計數

table1的

admin_id admin_name 
3   a 
4   b 
5   c 
6   d

表2

admin_id products 
3   pDeal 
3   pSeal  
4   pAeal 
5   pZeal 
6   pXeal  
3   pHeal 
6   pPeal

來源

2015-10-05 user4464505

你需要一個簡單的聯接和統計查詢：

SELECT table1.admin_name, COUNT(*) as cnt 
FROM 
    table1 INNER JOIN table2 
    ON table1.admin_id = table2.admin_id 
GROUP BY 
    table1.admin_name

來源

2015-10-05 06:37:34 fthiella

而不是INNER JOIN， LEFT JOIN在這裏最適合，不是嗎？由於admin_name不會被編入索引（在大多數情況下），因此列admin_name上的GROUPING可能會導致查詢緩慢！ – MaK

@MaK你可以通過'COUNT（*）'使用'INNER JOIN'或'COUNT（table2.admin_id）'使用'LEFT JOIN'，左連接將返回所有管理員，即使是那些有0個產品的管理員，內連接只有那些至少有1個產品 – fthiella

謝謝fthiella – user4464505

SELECT t1.admin_name, COUNT(t2.products) 
FROM table1 AS t1 LEFT JOIN table2 AS t2 ON t1.admin_id = t2.admin_id 
WHERE 1 
GROUP BY t2.admin_id

的LEFT JOIN將確保情況下，當表2沒有按對於某些管理員沒有任何記錄表1.

來源

2015-10-05 06:39:58 MaK

@ shA.t我不認爲它會。看看這個小提琴：http://sqlfiddle.com/#!9/9c086/2 – MaK

嘗試......

SELECT a.admin_name, COUNT(b.products) as 'CountOfProducts' 
    FROM table1 a INNER JOIN table2 b ON a.admin_id = b.admin_id 
    GROUP BY a.admin_name

來源

2015-10-05 06:44:30 Japongskie

這樣使用這個

SELECT adm.admin_name,COUNT(pdr.products) as ProductCnt 
FROM table1 AS adm 
JOIN table2 AS pdr 
    ON adm.admin_id = pdr.admin_id 
GROUP BY adm.admin_id;

來源

2015-10-05 06:51:23 Ninju

您可以使用內選擇：

SELECT 
    table1.admin_name, 
    (SELECT COUNT(*) 
    FROM table2 
    WHERE table1.admin_id = table2.admin_id) As cnt 
FROM 
    table1;

來源

2015-10-05 06:56:09

選擇加入SQL查詢計數

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