[英]How to count repeating values in a column in PostgreSQL?
這通常稱為間隙和孤島。
一種方法是使用兩個行號序列。
檢查查詢的每個中間結果以了解其工作原理。
WITH
CTE_rn
AS
(
SELECT
status
,dt
,ROW_NUMBER() OVER (ORDER BY dt) as rn1
,ROW_NUMBER() OVER (PARTITION BY status ORDER BY dt) as rn2
FROM
T
)
SELECT
status
,COUNT(*) AS cnt
FROM
CTE_rn
GROUP BY
status
,rn1-rn2
ORDER BY
min(dt)
;
結果
| status | cnt |
|---------|-----|
| offline | 2 |
| idle | 1 |
| offline | 2 |
| idle | 1 |
WITH
cte1 AS ( SELECT status,
"date",
workstation,
CASE WHEN status = LAG(status) OVER (PARTITION BY workstation ORDER BY "date")
THEN 0
ELSE 1 END changed
FROM test ),
cte2 AS ( SELECT status,
"date",
workstation,
SUM(changed) OVER (PARTITION BY workstation ORDER BY "date") group_num
FROM cte1 )
SELECT status, COUNT(*) "count", workstation, MIN("date") "from", MAX("date") "till"
FROM cte2
GROUP BY group_num, status, workstation;
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