asp.net - 如何使用 where 子句从 2 个不同的表中检索数据

Question

我有两个表[basic]，[info]都有一个主键email_id。现在我想从basic表中检索信息，但where子句应该从两个表中都有搜索条件

例子：

SELECT DISTINCT 
    basic.f_name, 
    basic.l_name 
FROM 
    basic 
CROSS JOIN 
    info 
WHERE 
    (basic.email_id = basic.email_id) 
    AND (basic.caste LIKE '%' + @caste + '%') 
    AND (info.diet =  @diet )

（此查询是用 asp 为 gridview 编写的，但它不起作用）

Answer 1

SELECT basic.f_name, basic.l_name 
FROM basic INNER JOIN info ON basic.email_id = info.email_id 
WHERE (basic.caste LIKE '%' + @caste + '%') AND (info.diet = @diet )

Answer 2

当您进行内部连接时，您实际上是在使用带有 where 子句的交叉连接。在内部连接中，所有数据都被组合（笛卡尔积），然后使用 where 子句进行过滤。因此，我认为您的代码使用内部连接会更干净。

SELECT DISTINCT basic.f_name, basic.l_name 
FROM basic 
CROSS JOIN info 
WHERE (basic.email_id = basic.email_id) 

相当于

SELECT basic.f_name, basic.l_name 
FROM basic INNER JOIN info ON basic.email_id = info.email_id 

我认为这可以解决您的问题。

Answer 3

使用内部联接

SELECT DISTINCT 
    basic.f_name, 
    basic.l_name 
FROM 
    basic as basic
INNER JOIN 
    info as info 
    ON basic.email_id = info.email_id
WHERE 
    (basic.caste LIKE '%' + @caste + '%') 
    AND (info.diet =  @diet )