解決方法：SUM命令內使用LAG命令

Question

我有查詢返回以下結果：

-- Get current int_type and compare with next int_type. If they are different, put 1. Then sum all results 
select CASE WHEN int_type <> LAG(int_type) OVER (ORDER BY id) THEN 1 END as next_int_type 
from data 

Output: 
0 
0 
0 
1 
1 
1 
0 
0 
0 
0 
0 
1 
0 
0 
0 
1 
0 
1 

使用SUM命令的內部時滯命令的問題：

select SUM(CASE WHEN int_type <> LAG(int_type) OVER (ORDER BY id) THEN 1 END) as next_int_type 
from data 

Error: ERROR: aggregate function calls cannot contain window function calls 

我如何可以總結上述結果在一個查詢中？

解決方法：

CREATE TEMP TABLE Temp AS 
    select SUM(CASE WHEN int_type <> LAG(int_type) OVER (ORDER BY id) THEN 1 END) as next_int_type 
    from data 

select SUM(CASE WHEN int_type <> next_int_type THEN 1 ELSE 0 END) Total 
from Temp ; 

Output: 6 

Answer 1

可以使用子查詢：

SELECT SUM(next_int_type) 
FROM (
    select CASE WHEN int_type <> LAG(int_type) OVER (ORDER BY id) THEN 1 END as next_int_type 
    from data 
) sub