MySQL:聚合计数

Question

我试图找出有多少公司在特定分割市场中有销售额。我已经设法统计了销售条目 (5)，但我似乎也无法按产品分割进行汇总。请看这个简化:

http://sqlfiddle.com/#!9/685cb/1

CREATE TABLE Table1
    (`company` text, `sales` int, `segment` text)
;

INSERT INTO Table1
    (`company`, `segment`, `sales`)
VALUES
    ('ACME',10,100),
    ('ACME',11,100),
    ('HAL',10,25),
    ('HAL',13,25),
    ('GEN',11,50)
;

SELECT COUNT(company) AS companies,
CASE 
    WHEN segment IN (10, 11, 12, 13, 14, 15, 16)
    THEN 'Product segment A'
    WHEN segment IN (20, 21, 22)
    THEN 'Product segment B'
    WHEN segment IN (30)
    THEN 'Product segment C'
    END AS grp, SUM(sales) AS sum_sales
FROM Table1
WHERE
       (company LIKE '%ACME%'
     OR company LIKE '%HAL%'
     OR company LIKE '%GEN%'
    )
AND
    segment IN (10, 11, 12, 13, 14, 15 ,16, 20, 21, 22, 30)
GROUP BY grp
ORDER BY grp
;

目标是让“公司”显示 3，因为在分割市场 A 中有 3 家公司有销售额。

Answer 1

您可以在 count 函数中使用 distinct 修饰符来获取不同 条目的数量:

SELECT COUNT(DISTINCT company) AS companies,
-- Here -----^
CASE 
    WHEN segment IN (10, 11, 12, 13, 14, 15, 16)
    THEN 'Product segment A'
    WHEN segment IN (20, 21, 22)
    THEN 'Product segment B'
    WHEN segment IN (30)
    THEN 'Product segment C'
    END AS grp, SUM(sales) AS sum_sales
FROM Table1
WHERE
       (company LIKE '%ACME%'
     OR company LIKE '%HAL%'
     OR company LIKE '%GEN%'
    )
AND
    segment IN (10, 11, 12, 13, 14, 15 ,16, 20, 21, 22, 30)
GROUP BY grp
ORDER BY grp
;

SQLFiddle