Question

你好我是postgresql的新手。这是我的代码，用于对选项进行分组并对其进行计数。我想要一种方法来获得最大计数的选项。有什么办法吗？

SELECT s.option, COUNT(*)
FROM "Set" as s, "Lecture" as l, "Process" as p, "donation" as d
WHERE d.code = p.code and l.type = p.type and l.option = s.option
GROUP BY s.option

Answer 1

只需为孩子命名（例如count），ORDER BY该名称，LIMIT为1：

SELECT s.option, COUNT(*) AS count -- give the child a name
FROM "Set" as s, "Lecture" as l, "Process" as p, "donation" as d
WHERE d.code = p.code and l.type = p.type and l.option = s.option
GROUP BY s.option
ORDER BY count DESC -- order by that child in descending order
LIMIT 1 -- and limit the output to one row

如果您想要最高，则应将DESC添加到ORDER BY。如果你想要最低;要么不指定，要么添加ASC。

Answer 2

您可以简化查询。不仅可以使用PROPER，显式JOIN语法，还可以删除Set：

SELECT l.option, COUNT(*)
FROM "Lecture" l JOIN
     "Process" p
     ON l.type = p.type JOIN
     "donation" d
     ON d.code = p.code
GROUP BY l.option
ORDER BY COUNT(*) DESC
FETCH FIRST 1 ROW ONLY;

在GROUP BY查询中查找最高COUNT

2 个答案: