case语句中出现缺少表达式错误

Question

我的源表Test包含id列，目标表testm由id , col2组成。请帮助我摆脱这个错误。

test (source)                  

 id                              
---                              
 10                     
 10 
 20 
 20 
 20 
 30 
 30 
 40 

目标

testm 

id  col2                
--  ----                
10  1                 
10  2         
20  1          
20  2          
20  3          
30  1          
30  2          
40  1          

查询：

select id, (case id 
            when 10 then select count(id) from test where id =10
            when 20 then select count(id) from test where id =20
            when 30 then select count(id) from test where id =30
            when 40 then select count(id) from test where id =40
else 0 END ) col2 from test

抛出错误：

  

缺少表达

Answer 1

通过查看所需的输出，我猜你想按组对每次出现的id进行编号;如果是这种情况，使用row_number分析函数应该做你想要的：

select id, row_number() over (partition by id order by id) as col2
from test
order by id;

请参阅此示例SQL Fiddle

给定样本源数据，这将是输出：

| ID | COL2 |
|----|------|
| 10 |    1 |
| 10 |    2 |
| 20 |    1 |
| 20 |    2 |
| 20 |    3 |
| 30 |    1 |
| 30 |    2 |
| 40 |    1 |