Question

我的查询：

SELECT * 
FROM tvn_Listing 
LEFT JOIN tvn_ListingOption ON (tvn_Listing.id = tvn_ListingOption.listings_id 
                                AND tvn_ListingOption.options_id = 12)

当我离开加入两个表时如何删除空记录？我的查询返回的结果不是条件指定的结果。

Answer 1

如果我正确理解你的问题，问题是：

您可以从tvn_Listing表中获取NULL ed table LEFT JOIN中tvn_ListingOption个值的记录。那么你可以检查tvn_ListingOption表中的空值，如：

SELECT * 
FROM tvn_Listing 
LEFT JOIN tvn_ListingOption ON (tvn_Listing.id = tvn_ListingOption.listings_id 
                                AND tvn_ListingOption.options_id = 12)
WHERE tvn_ListingOption.Id IS NOT NULL

Answer 2

请注意，添加NOT NULL条件会影响结果（如果options_id为NULLABLE）

test=# select * from tvn_Listing;
 id | nm 
----+----
  1 | A
  2 | B
(2 rows)

test=# select * from tvn_listingoption ;
 id | op 
----+----
  1 | A
  3 | B
    | D
(3 rows)

test=# select * from tvn_listing left join tvn_listingoption on tvn_listing.id=tvn_listingoption.id;
 id | nm | id | op 
----+----+----+----
  1 | A  |  1 | A
  2 | B  |    | 
(2 rows)

test=# select * from tvn_listing left join tvn_listingoption on tvn_listing.id=tvn_listingoption.id and tvn_listingoption.id is not null ;
 id | nm | id | op 
----+----+----+----
  1 | A  |  1 | A
  2 | B  |    | 
(2 rows)

test=# select * from tvn_listing left join tvn_listingoption on tvn_listing.id=tvn_listingoption.id where  tvn_listingoption.id is not null ;
 id | nm | id | op 
----+----+----+----
  1 | A  |  1 | A
(1 row)

如何在筛选SQL QUERY之前删除

2 个答案: