Question

Hii我想在单个查询中使用不同条件从同一列中获取值两次

这是我的代码

SELECT
    o.products_options_name,
    ov.products_options_values_name AS products_options_values_name,
    a.options_values_quantity  
FROM
    table_products_options o,
    table_products_attributes a
WHERE
    a.options_id = o.products_options_id
    AND 
    o.products_options_values_id = a.options_values_id 
    AND
    a.products_id = :products_id 
    AND
    a.options2_values_id = options2_values_id

我想再次使用不同的条件获取列products_options_values_name的值，例如同一查询中的a.options2_values_id = ov.products_options_values_id。我怎么能这样做？

Answer 1

尝试使用UNION运算符

SELECT o.products_options_name, ov.products_options_values_name AS products_options_values_name,
a.options_values_quantity  
FROM 
table_products_options o, table_products_attributes a
WHERE 
a.options_id = o.products_options_id AND ov.products_options_values_id = a.options_values_id 
AND a.products_id = :products_id1 AND 
a.options2_values_id = options2_values_id 

UNION 

SELECT o.products_options_name, ov.products_options_values_name AS products_options_values_name,
 a.options_values_quantity  
FROM 
table_products_options o, table_products_attributes a
WHERE 
a.options_id = o.products_options_id AND ov.products_options_values_id = a.options_values_id
AND a.products_id = :products_id2 AND 
a.options2_values_id = options2_values_id

Answer 2

Union / Union都是最好的

喜欢

select o.products_options_name, ov.products_options_values_name as     
products_options_values_name, a.options_values_quantity  
from 
table_products_options o, table_products_attributes a
where 
a.options_id = o.products_options_id and ov.products_options_values_id =     
a.options_values_id and a.products_id = :products_id and  a.options2_values_id = 
options2_values_id 

UNION 

select o.products_options_name, ov.products_options_values_name as products_options_values_name, a.options_values_quantity  
from 
table_products_options o, table_products_attributes a
where Diffrent Clause

Union Works就像Distinct一样，如果你的子句都返回值，则Union ALL将返回重复值。

或者在where子句and (a.b = c.d OR c.d=b.a) and

中使用OR

Answer 3

您可以在on子句中指定所需的条件。 on条款？您的查询应使用显式join语法。

以下是表达所需查询的一种方法：

select o.products_options_name, ov.products_options_values_name as products_options_values_name, 
       a.options_values_quantity  
from table_products_options o join
     table_products_attributes a
     on a.options_id = o.products_options_id and
        (ov.products_options_values_id = a.options_values_id or
         a.options2_values_id = options2_values_id
        )
where a.products_id = :products_id;

在单个查询中，使用不同条件从同一列中获取两次值

3 个答案: