根据另一列的值删除一列上的重复值

Question

我有一张名为Table1 的表格，见下文

PRODUCT    CUSTOMER               COMP
DICE       DAVES PET SHOP         Billed
DICE       CLAXTONS               ToT
CARDS      VIEWSONIC              NITS
CARDS      NORTHERN LIGHTS        Billed
CARDS      NORTHERN LIGHTS        NITS
BOX        TABLEAU                Billed
BOX        TABLEAU                ToT

有些值在 CUSTOMER 字段中有重复项，但如果重复，它将始终在至少一个 COMP 部分中包含 Billed，因此我希望生成的查询仅返回 COMP 中的值，其中重复项为 Billed，因此结果表看起来像

PRODUCT    CUSTOMER               COMP
DICE       DAVES PET SHOP         Billed
DICE       CLAXTONS               ToT
CARDS      VIEWSONIC              NITS
CARDS      NORTHERN LIGHTS        Billed
BOX        TABLEAU                Billed

这是我尝试过的 SQL

SELECT * 
FROM Table1
WHERE COMP = 'Billed'
UNION ALL
SELECT Table1_A.PRODUCT, Table1_A.CUSTOMER, Table1_A.COMP
FROM Table1 Table1_A
LEFT JOIN (
    SELECT * 
    FROM Table1 
    WHERE COMP != 'Billed'
) Table1_B ON Table1_B.PRODUCT = Table1_A.PRODUCT 
    AND Table1_B.CUSTOMER = Table1_A.CUSTOMER

我想如果我输入一个UNION 并引用两个等于Billed 而不等于Billed，那么它将保持我正在寻找的格式，但它只是重复每个CUSTOMER每一个COMP

Answer 1

您可以对规则使用聚合：

SELECT PRODUCT, CUSTOMER, 
       (CASE WHEN COUNT(*) = 1 THEN MAX(COMP) ELSE 'Billed' END)
FROM table1 
GROUP BY PRODUCT, CUSTOMER;

您也可以使用UNION ALL 方法：

select product, customer, comp
from table1 t1
where comp = 'Billed'
union all
select product, customer, comp
from table1 t1
where not exists (select 1
                  from table1 tt1
                  where tt1.product = t1.product and
                        tt1.customer = t1.customer and
                        tt1.comp = 'Billed'
                 );