如何將表與多個工會進行比較並加入？

Question

我試圖找到只存在於一個表中的行。大表名（由所有行組成）是kwf_uploads，以許多名字出現的小表。我的目標是找到存在於kwf_uploads中的行，但不存在於其他位置（這個例子是沒有關係的表中的主鍵和外鍵）。

我在SQL做了什麼：

select id from 
kwf_uploads 
left join 

(SELECT picture_id as id 
FROM documents where picture_id is not null 
UNION 
SELECT file_id as id 
FROM books where file_id is not null 
UNION 
SELECT picture_id as id 
FROM employee where picture_id is not null 
UNION 
SELECT file_id as id 
FROM flightFiles where file_id is not null 
UNION 
SELECT picture_id as id 
FROM tasks where picture_id is not null 
UNION 
SELECT picture_id as id 
FROM trainingContentQuestions where picture_id is not null 
UNION 
SELECT picture_id as id 
FROM trainingQuestions where picture_id is not null) foo 

ON kwf_uploads.id = foo.id 

找到它：SQL: cascade UNION and JOIN

但它失敗，錯誤：SQL (1052): Column "id" in field list is ambiguous。

我不想在每個表中使用連接，因爲我不擅長連接，並且sql變得非常大且不可讀。我也試過not exists沒有任何結果。 我認爲，我們可以找到一個更好的解決方案=）

導致select id from kwf_uploads查詢（9690行）：

從聯合查詢結果（6096行）：

結果我想看到3594（9690減去6096）行。

Answer 1

UNION（單獨使用時，沒有ALL）是一個「昂貴」的操作。

有一個替代方案，不存在。這個構造是一個「半連接」，我懷疑可能比聯合方法更便宜。

SELECT 
     id 
FROM kwf_uploads AS u 
WHERE NOT EXISTS  (SELECT NULL FROM documents WHERE u.id = picture_id) 
     AND NOT EXISTS (SELECT NULL FROM books WHERE u.id = file_id) 
     AND NOT EXISTS (SELECT NULL FROM employee WHERE u.id = picture_id) 
     AND NOT EXISTS (SELECT NULL FROM flightFiles WHERE u.id = file_id) 
     AND NOT EXISTS (SELECT NULL FROM tasks WHERE u.id = picture_id) 
     AND NOT EXISTS (SELECT NULL FROM trainingContentQuestions WHERE u.id = picture_id) 
     AND NOT EXISTS (SELECT NULL FROM trainingQuestions WHERE u.id = picture_id) 

Answer 2

要解決當前的錯誤與正確的結果集別名

前綴ID列。在這種情況下，kwf_uploads.id。由於Id存在於兩個結果集中。

，從而獲得所需的輸出

添加Where foo.id is null。這將獲取那些加入失敗的ID，那些是你想要的ID。

select kwf_uploads.id from 
     kwf_uploads 
     left join 

     (SELECT picture_id as id 
     FROM documents where picture_id is not null 
     UNION 
     SELECT file_id as id 
     FROM books where file_id is not null 
     UNION 
     SELECT picture_id as id 
     FROM employee where picture_id is not null 
     UNION 
     SELECT file_id as id 
     FROM flightFiles where file_id is not null 
     UNION 
     SELECT picture_id as id 
     FROM tasks where picture_id is not null 
     UNION 
     SELECT picture_id as id 
     FROM trainingContentQuestions where picture_id is not null 
     UNION 
     SELECT picture_id as id 
     FROM trainingQuestions where picture_id is not null) foo 

     ON kwf_uploads.id = foo.id 
     where foo.id is null 

Answer 3

除了DarkKnight答案：

您不需要包括每個union selectwhere。最糟糕的情況下，你從所有UNION得到一個NULL但不會出現在LEFT JOIN反正

select kwf_uploads.id 
from kwf_uploads 
left join 
    (
    SELECT picture_id as id FROM documents 
    UNION 
    SELECT file_id as id FROM books 
    UNION 
    SELECT picture_id as id FROM employee 
    UNION 
    SELECT file_id as id FROM flightFiles 
    UNION 
    SELECT picture_id as id FROM tasks 
    UNION 
    SELECT picture_id as id FROM trainingContentQuestions 
    UNION 
    SELECT picture_id as id FROM trainingQuestions 
    ) foo  
ON kwf_uploads.id = foo.id 
where foo.id is null