选择加入SQL查询计数

如何使用查询分别查看a，b，c，d添加的产品数量？选择加入SQL查询计数

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

来源

2015-10-05 user4464505

你需要一个简单的联接和统计查询：

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

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2015-10-05 06:37:34 fthiella

而不是INNER JOIN， LEFT JOIN在这里最适合，不是吗？由于admin_name不会被编入索引（在大多数情况下），因此列admin_name上的GROUPING可能会导致查询缓慢！ – MaK

@MaK你可以通过'COUNT（*）'使用'INNER JOIN'或'COUNT（table2.admin_id）'使用'LEFT JOIN'，左连接将返回所有管理员，即使是那些有0个产品的管理员，内连接只有那些至少有1个产品 – fthiella

谢谢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将确保情况下，当表2没有按对于某些管理员没有任何记录表1.

来源

2015-10-05 06:39:58 MaK

@ shA.t我不认为它会。看看这个小提琴：http://sqlfiddle.com/#!9/9c086/2 – MaK

尝试......

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

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2015-10-05 06:44:30 Japongskie

这样使用这个

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;

来源

2015-10-05 06:51:23 Ninju

您可以使用内选择：

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

来源

2015-10-05 06:56:09

选择加入SQL查询计数

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