Question

我需要帮助编写一个SQL语句，该语句将从两个不同的表创建一个SQL视图，从每个可能性中捕获2条记录。

例如，如果customer表中有三条记录与GROUP A的{{1}}和STATE匹配，那么您应该只显示视图中3条记录中的2条记录 - 但是如果如果客户位于NV和GROUP A STATE或PA和GROUP B，则还需要在视图中捕获这些附加记录。

我是SQL新手。我的想法都没有奏效，所以我感谢任何有助于我解决问题的反馈。以下查询是我设法写的：

STATE of NV

以下是它产生的观点：

 SELECT customer_table.Customer_ID,
    customer_table.First_Name,
    customer_table.Last_Name,
    customer_table.Email_Address,
    customer_table.STATE,
    customer_table.GROUP_,
    customer_table.Timestamp_,
    product_table.Prod_Name,
    product_table.Prod_desc
FROM customer_table
INNER JOIN product_table ON customer_table.Customer_ID = product_table.Customer_ID
ORDER BY customer_table.STATE,
    customer_table.GROUP_;

Answer 1

我相信你最好的选择是UNION查询。这会将两个单独的SELECT语句的结果叠加在一起。此外，您可以使用WHERE子句过滤这两个查询。第二个将有点棘手，因为你有两个条件，所以我们将使用OR来分隔它们。

/* First SELECT finds two records in Nevada for Group A*/
SELECT TOP 2 
    customer_table.Customer_ID,
    customer_table.First_Name,
    customer_table.Last_Name,
    customer_table.Email_Address,
    customer_table.STATE,
    customer_table.GROUP_,
    customer_table.Timestamp_,
    product_table.Prod_Name,
    product_table.Prod_desc
FROM customer_table
INNER JOIN product_table ON customer_table.Customer_ID = product_table.Customer_ID
WHERE customer_Table.GROUP_ = 'A' AND customer_table.STATE = 'NV'

/*UNION ALL will stack the results of these two queries into a single result set*/
UNION ALL

/*Second SELECT finds all records for PA, GROUP A  and NV, GROUP B*/
SELECT 
    customer_table.Customer_ID,
    customer_table.First_Name,
    customer_table.Last_Name,
    customer_table.Email_Address,
    customer_table.STATE,
    customer_table.GROUP_,
    customer_table.Timestamp_,
    product_table.Prod_Name,
    product_table.Prod_desc
FROM customer_table
INNER JOIN product_table ON customer_table.Customer_ID = product_table.Customer_ID
WHERE (customer_table.GROUP_ = 'A' AND customer_Table.STATE = 'PA') OR
    (customer_table.GROUP_ = 'B' AND customer_table.STATE = 'NV')

最后，TOP 2是SQL Server语法，如果这是MYSQL，则说“仅返回此结果集的前两个记录”，然后取出TOP 2并粘贴{{ 1}}在LIMIT 2语句的末尾代替。

需要帮助编写SQL语句

1 个答案: