Question

我有一个简单的表格，我存储了一堆股票的市值。我试图看看我是否可以创建一个返回类似以下内容的查询：

cap_type  type_count
micro     4
small     6
large     1
mega      2

我不确定如何调整此查询以计算不同选择案例组中的cap_types数量。这就是我到目前为止所拥有的：

SELECT CASE
    WHEN market_cap < 10 THEN 'micro' 
    WHEN market_cap >= 10 < 50 THEN 'small' 
    WHEN market_cap >= 50 < 100 THEN 'large' 
    ELSE 'mega' 
END AS cap_type
FROM stocks
GROUP BY CASE
    WHEN market_cap < 10 THEN 'micro' 
    WHEN market_cap >= 10 < 50 THEN 'small' 
    WHEN market_cap >= 50 < 100 THEN 'large' 
    ELSE 'mega' 
    END
ORDER BY cap_type ASC

以下是一些示例数据：

CREATE TABLE `stocks` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `stock` varchar(4) COLLATE utf8_unicode_ci DEFAULT NULL,
  `market_cap` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
)
INSERT INTO temp (`stock`,`market_cap`) VALUES ('MSFT', 40);
INSERT INTO temp (`stock`,`market_cap`) VALUES ('MINI', 4);
INSERT INTO temp (`stock`,`market_cap`) VALUES ('GOOG', 50);
INSERT INTO temp (`stock`,`market_cap`) VALUES ('F', 90);

Answer 1

您可以使用子查询：

SELECT sub.cap_type, COUNT(*) AS type_count
FROM (
    SELECT CASE WHEN market_cap < 10 THEN 'micro' 
                WHEN market_cap < 50 THEN 'small' 
                WHEN market_cap < 100 THEN 'large' 
                ELSE 'mega' 
           END AS cap_type
    FROM temp
) AS sub  
GROUP BY sub.cap_type
ORDER BY 
CASE sub.cap_type
  WHEN 'micro' THEN 1
  WHEN 'small' THEN 2
  WHEN 'large' THEN 3
  ELSE 4
END;

的 SqlFiddleDemo

或仅向您现有的查询添加COUNT(*)：

SELECT CASE WHEN market_cap < 10 THEN 'micro' WHEN market_cap < 50 THEN 'small' WHEN market_cap < 100 THEN 'large' ELSE 'mega' END AS cap_type ,COUNT(*) AS type_count FROM temp GROUP BY CASE WHEN market_cap < 10 THEN 'micro' WHEN market_cap < 50 THEN 'small' WHEN market_cap < 100 THEN 'large' ELSE 'mega' END ORDER BY CASE cap_type WHEN 'micro' THEN 1 WHEN 'small' THEN 2 WHEN 'large' THEN 3 ELSE 4 END

如果您需要所有组，可以使用子查询列出它们并LEFT JOIN：

SELECT sub.cap_type, COUNT(t.market_cap) AS type_count FROM (SELECT 'micro' AS cap_type UNION ALL SELECT 'small' UNION ALL SELECT 'large' UNION ALL SELECT 'mega') AS sub LEFT JOIN temp t ON CASE WHEN t.market_cap < 10 THEN 'micro' WHEN t.market_cap < 50 THEN 'small' WHEN t.market_cap < 100 THEN 'large' ELSE 'mega' END = sub.cap_type GROUP BY sub.cap_type ORDER BY CASE cap_type WHEN 'micro' THEN 1 WHEN 'small' THEN 2 WHEN 'large' THEN 3 ELSE 4 END

的 SqlFiddleDemo2

输出：

╔═══════════╦════════════╗ ║ cap_type ║ type_count ║ ╠═══════════╬════════════╣ ║ micro ║ 1 ║ ║ small ║ 1 ║ ║ large ║ 2 ║ ║ mega ║ 0 ║ ╚═══════════╩════════════╝

Answer 2

您是否尝试过以下操作？或者我是否理解错误的问题？

SELECT 
  CASE
    WHEN market_cap < 10 THEN 'micro' 
    WHEN market_cap >= 10 < 50 THEN 'small' 
    WHEN market_cap >= 50 < 100 THEN 'large' 
    ELSE 'mega' 
  END AS cap_type,
  COUNT(*) as count
FROM stocks
GROUP BY cap_type
ORDER BY cap_type ASC;

UPD：您的CASE语句包含细微错误（您错过了AND，条件没有意义，但形式上是正确的），这是正确的查询（匹配WHEN条件停止处理）：

SELECT 
  CASE
    WHEN market_cap < 10 THEN 'micro' 
    WHEN market_cap < 50 THEN 'small' 
    WHEN market_cap < 100 THEN 'large' 
    ELSE 'mega' 
  END AS cap_type,
  COUNT(*) as count
FROM stocks
GROUP BY cap_type
ORDER BY cap_type ASC;

Answer 3

SELECT 
CASE
    WHEN market_cap < 10 THEN 'micro'
    WHEN market_cap >= 10 and market_cap < 50 THEN 'small'
    WHEN market_cap >= 50 and market_cap < 100 THEN 'large'
    ELSE 'mega'
END AS cap_type,
count(*)
FROM stock
GROUP BY CASE
    WHEN market_cap < 10 THEN 'micro'
    WHEN market_cap >= 10 and market_cap < 50 THEN 'small'
    WHEN market_cap >= 50 and market_cap < 100 THEN 'large'
    ELSE 'mega'
END
ORDER BY cap_type ASC;

SQLFiddle.

mySQL：CASE，GROUP和ORDER By

3 个答案: