SQL：如何根據兩個字段查找重複項？

Question

我在Oracle數據庫表中有行，對於兩個字段的組合應該是唯一的，但是在表上沒有設置唯一約束，所以我需要查找所有使用SQL自行違反約束的行。不幸的是，我微薄的SQL技能不能勝任。

我的表格有三個相關的列：entity_id，station_id和obs_year。對於每一行，station_id和obs_year的組合應該是唯一的，並且我想通過用SQL查詢來清除它們是否存在違反這些行的行。

我曾嘗試以下SQL（由this previous question建議），但它不爲我工作（我得到含糊不清的ORA-00918列）：

SELECT 
entity_id, station_id, obs_year 
FROM 
mytable t1 
INNER JOIN (
SELECT entity_id, station_id, obs_year FROM mytable 
GROUP BY entity_id, station_id, obs_year HAVING COUNT(*) > 1) dupes 
ON 
t1.station_id = dupes.station_id AND 
t1.obs_year = dupes.obs_year 

可有人建議我做錯了什麼，和/或如何解決這個問題？您查詢的

Answer 1

SELECT * 
FROM (
     SELECT t.*, ROW_NUMBER() OVER (PARTITION BY station_id, obs_year ORDER BY entity_id) AS rn 
     FROM mytable t 
     ) 
WHERE rn > 1 

Answer 2

重新寫

SELECT 
t1.entity_id, t1.station_id, t1.obs_year 
FROM 
mytable t1 
INNER JOIN (
SELECT entity_id, station_id, obs_year FROM mytable 
GROUP BY entity_id, station_id, obs_year HAVING COUNT(*) > 1) dupes 
ON 
t1.station_id = dupes.station_id AND 
t1.obs_year = dupes.obs_year 

我覺得不明確的列錯誤（ORA-00918），是因爲你的select荷蘭國際集團列的名字出現在表和子查詢都，但你沒有如果你想要dupes或mytable（別名爲t1）。

Answer 3

您不可以創建一個包含唯一約束的新表，然後逐行復制數據行，忽略故障嗎？

Answer 4

更改初始選擇的3場是

SELECT 
t1.entity_id, t1.station_id, t1.obs_year 

Answer 5

SELECT entity_id, station_id, obs_year 
FROM mytable t1 
WHERE EXISTS (SELECT 1 from mytable t2 Where 
     t1.station_id = t2.station_id 
     AND t1.obs_year = t2.obs_year 
     AND t1.RowId <> t2.RowId) 

Answer 6

你需要指定表主選擇列。此外，假設entity_id是mytable的唯一鍵，並且與查找重複項無關，您不應該在dupes子查詢中對其進行分組。

嘗試：

SELECT t1.entity_id, t1.station_id, t1.obs_year 
FROM mytable t1 
INNER JOIN (
SELECT station_id, obs_year FROM mytable 
GROUP BY station_id, obs_year HAVING COUNT(*) > 1) dupes 
ON 
t1.station_id = dupes.station_id AND 
t1.obs_year = dupes.obs_year 

Answer 7

SELECT * 
FROM (
     SELECT t.*, ROW_NUMBER() OVER (PARTITION BY station_id, obs_year ORDER BY entity_id) AS rn 
     FROM mytable t 
     ) 
WHERE rn > 1 

由Quassnoi是最高效的大表。 我有這個分析成本：

SELECT a.dist_code, a.book_date, a.book_no 
FROM trn_refil_book a 
WHERE EXISTS (SELECT 1 from trn_refil_book b Where 
     a.dist_code = b.dist_code and a.book_date = b.book_date and a.book_no = b.book_no 
     AND a.RowId <> b.RowId) 
     ; 

給了1322341

SELECT a.dist_code, a.book_date, a.book_no 
FROM trn_refil_book a 
INNER JOIN (
SELECT b.dist_code, b.book_date, b.book_no FROM trn_refil_book b 
GROUP BY b.dist_code, b.book_date, b.book_no HAVING COUNT(*) > 1) c 
ON 
a.dist_code = c.dist_code and a.book_date = c.book_date and a.book_no = c.book_no 
; 

成本給了1271699

而

SELECT dist_code, book_date, book_no 
FROM (
     SELECT t.dist_code, t.book_date, t.book_no, ROW_NUMBER() OVER (PARTITION BY t.book_date, t.book_no 
      ORDER BY t.dist_code) AS rn 
     FROM trn_refil_book t 
     ) p 
WHERE p.rn > 1 
; 

給了1021984成本費用

該表沒有索引....

Answer 8

SELECT entity_id, station_id, obs_year 
    FROM mytable 
GROUP BY entity_id, station_id, obs_year 
HAVING COUNT(*) > 1 

指定字段找到關於SELECT和GROUP BY都重複。

它的工作原理是利用GROUP BY找到匹配基於指定列的其他行的任何行。 該HAVING COUNT(*) > 1說，我們只有興趣看到任何行發生超過1次（因此重複）