Question

如何使用ROW_NUMBER（）函数（必需）在Mysql表显示上显示行号？

mysql> select * from work;
+------+-----------+
| name | work_days |
+------+-----------+
| john |         5 |
| jane |         7 |
| jane |         2 |
| john |         3 |
+------+-----------+
4 rows in set (0.01 sec)

不使用ROW_NUMBER（）：

mysql> SELECT name, 
    -> AVG(work_days) AS workday_average, 
    -> COUNT(*) as count
    -> FROM work
    -> GROUP BY name
    -> HAVING workday_average > 2
    -> ORDER BY workday_average ASC, count DESC;
+------+-----------------+-------+
| name | workday_average | count |
+------+-----------------+-------+
| john |          4.0000 |     2 |
| jane |          4.5000 |     2 |
+------+-----------------+-------+
2 rows in set (0.00 sec)

尝试使用ROW_NUMBER（）添加行号列时出现以下错误。

mysql> SELECT name, 
    -> ROW_NUMBER() over(PARTITION BY name ORDER BY work_days) as row_num,
    -> AVG(work_days) AS workday_average, 
    -> COUNT(*) as count
    -> FROM work
    -> GROUP BY name
    -> HAVING workday_average > 2
    -> ORDER BY workday_average ASC, count DESC;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '(PARTITION BY name ORDER BY work_days) as row_num,
AVG(work_days) AS workday_ave' at line 2
mysql>

Answer 1

窗口函数在GROUP BY聚合发生之后进行评估，因此在name上使用分区没有多大意义，因为可以保证此时的每个记录都具有不同的名称。您最有可能想要这样的东西：

SELECT
    name, 
    ROW_NUMBER() OVER (ORDER BY AVG(work_days), COUNT(*) DESC) AS row_num,
    AVG(work_days) AS workday_average, 
    COUNT(*) AS count
FROM work
GROUP BY
    name
HAVING
   workday_average > 2
ORDER BY
    workday_average,
    count DESC;

但是，这当然假设您使用的是MySQL 8+。如果没有，则ROW_NUMBER将不可用。

如何使用ROW_NUMBER（）向MySQL显示添加行号

1 个答案: