Question

我有两个桌子。表A：

Vendor  Amount
001      1000
002      500

表B：

Vendor   payday  Amount paid 
001       190101      600
001       190201      200
002       190201      100

我可以使用SQL获得以下结果

Vendor   Amount   payday     paidamount
 001       1000     190101       600
001                 190201       200
002         500     190201       100

让不同数量仅显示一次吗？谢谢。

Answer 1

如果RDBMS支持窗口功能，我将为此使用LAG()，因为它避免了使用子查询：

SELECT
    ta.vendor, 
    CASE WHEN ta.amount = LAG(ta.amount) OVER(PARTITION BY ta.vendor ORDER BY tb.payday, tb.amount DESC) THEN NULL ELSE ta.amount END amount,
    tb.payday, 
    tb.amount
FROM tablea ta
INNER JOIN tableb tb ON ta.vendor = tb.vendor
ORDER BY 
    ta.vendor, 
    ta.amount, 
    tb.payday, 
    tb.amount

此 MySQL DB Fiddle 返回：

| vendor | amount | payday | amount |
| ------ | ------ | ------ | ------ |
| 1      |        | 190101 | 200    |
| 1      | 1000   | 190101 | 600    |
| 2      | 500    | 190101 | 100    |

Answer 2

使用大多数数据库管理系统支持的row_number()

select Vendor,
case when rn>1 then null else Amount end as Amount,
payday,paidamount from    
(select a.Vendor,a.Amount,b.payday,b.paidamount,
 row_number() over(partition by a.Vendor order by a.Amount) rn from
tableA a join tableB b on a.Vendor=b.Vendor
) t

demo link 输出

Vendor  Amount  payday  paidamount
1       1000    190101  600
1               190101  200
2       500     190101  100

Answer 3

您绝对不需要子查询来使用row_number()：

SELECT ta.vendor, 
       (CASE WHEN 1 = ROW_NUMBER() OVER (PARTITION BY ta.vendor ORDER BY tb.payday, tb.amount DESC)
             THEN ta.amount
        END) as amount,
       tb.payday, tb.amount
FROM tablea ta INNER JOIN
     tableb tb
     ON ta.vendor = tb.vendor
ORDER BY ta.vendor, tb.payday, tb.amount DESC;

从左外部联接中删除重复项

3 个答案: