如何在SQL中统计并排序数据表指定列的条目出现次数

该需求完全可以通过SQL实现，核心注意事项是带空格的字段名completed at需要用对应数据库的标识符转义符包裹，以下是不同主流数据库的适配写法：

• MySQL 环境（用反引号包裹带空格标识符）：

SELECT
  COUNT(*) AS `Count`,
  `completed at` AS `Location`
FROM completed
WHERE `completed at` != 'blank entry'
GROUP BY `completed at`
ORDER BY `Count` DESC;

• PostgreSQL、SQLite 环境（用双引号包裹带空格标识符）：

SELECT
  COUNT(*) AS "Count",
  "completed at" AS "Location"
FROM completed
WHERE "completed at" != 'blank entry'
GROUP BY "completed at"
ORDER BY "Count" DESC;

• SQL Server 环境（用方括号包裹带空格标识符）：

SELECT
  COUNT(*) AS [Count],
  [completed at] AS [Location]
FROM completed
WHERE [completed at] != 'blank entry'
GROUP BY [completed at]
ORDER BY [Count] DESC;

以上语句会自动过滤blank entry的记录，仅统计三类目标值的出现频次，输出列名、排序规则完全匹配要求。

内容的提问来源于stack exchange，提问作者Lars