英文:
"Operational Error: row value misused" error
问题
我从一个sqlite3查询中得到了一个错误，但找不到原因。
创建表格：
CREATE TABLE professors (
firstname text,
lastname text,
university_shortname text
);
查询：
SELECT COUNT(DISTINCT(firstname, lastname)) FROM professors;
错误信息：
OperationalError: 行值被误用
英文:
I'm getting an error from an sqlite3 query for which I can't find the reason.
CREATE TABLE professors (
firstname text,
lastname text,
university_shortname text
);
Query:
SELECT COUNT(DISTINCT(firstname, lastname)) FROM professors;
Error:
> OperationalError: row value misused
答案1
得分: 1
COUNT() 聚合函数只接受1个参数，该参数不能是像 (firstname, lastname) 这样的行值。<br/>
您的需求的一个解决方法是使用 DENSE_RANK() 窗口函数：
SELECT DENSE_RANK() OVER (ORDER BY firstname, lastname) AS distinct_count
FROM professors
ORDER BY distinct_count DESC LIMIT 1;
查看一个简化的演示。<br/>
请注意，上述查询将计算所有不同的 firstname 和 lastname 组合，即使其中一个或两个列为空。
英文:
COUNT() aggregate function takes only 1 argument and that argument can't be a row value like (firstname, lastname).<br/>
A workaround for your requirement would be the use of DENSE_RANK() window function:
SELECT DENSE_RANK() OVER (ORDER BY firstname, lastname) AS distinct_count
FROM professors
ORDER BY distinct_count DESC LIMIT 1;
See a simplified demo.<br/>
Note that the above query will count all the distinct combinations of firstname and lastname, even the ones where one or both columns are null.
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