mySQL:CASE、GROUP 和 ORDER By

Question

我有一个简单的表，其中存储了一堆股票的市值。我正在尝试查看是否可以创建一个将返回如下内容的查询:

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 cap_types 的数量。这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

这是一些示例数据:

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

您是否尝试过以下方法？还是我理解错了？

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，并且条件没有意义，尽管在形式上是正确的)，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;