此查询：

select sku
from tablename
group by sku
having 
  max(case when properties = 'Family_ID' then value end) = 21
  and
  max(case when properties = 'Class_ID' then value end) = 21

返回所有 sku 满足你的条件的，你可以和操作符一起使用 IN 这样地：

select * from tablename
where sku in (
  select sku
  from tablename
  group by sku
  having 
    max(case when properties = 'Family_ID' then value end) = 21
    and
    max(case when properties = 'Class_ID' then value end) = 21
)

也可以使用max（）窗口函数：

select t.sku, t.properties, t.value
from (
  select *,
    max(case when properties = 'Family_ID' then value end) over (partition by sku) family_id,
    max(case when properties = 'Class_ID' then value end) over (partition by sku) class_id
  from tablename  
) t  
where t.family_id = 21 and t.class_id = 21

请看演示。
结果：

> sku | properties | value
> --: | :--------- | ----:
>   1 | Family_ID  |    21
>   1 | Class_ID   |    21
>   3 | Family_ID  |    21
>   3 | Class_ID   |    21

要跨行操作，您需要分组，但这里最简单的事情（考虑到您似乎希望此主题有更多的变体）可能是数据透视：

WITH x as(
 SELECT f.sku, c.value as class_value, f.value as family_value
 FROM
  (select sku, value FROM table WHERE properties = 'family_id') f
  INNER JOIN
  (select sku, value FROM table WHERE properties = 'class_id') c
  ON f.sku = c.sku
)

现在可以使用where子句，如normal：

SELECT * FROM x WHERE family_value = 20 and class_value = 21

如果需要以列格式返回数据，可以再次取消打印：

SELECT
  sku,
  'family_id' as properties,
  family_value as value
FROM 
  x
UNION ALL
SELECT
  sku,
  'class_id' as properties,
  class_value as value
FROM 
  x

但只处理数据透视形式的数据可能更容易。
我自己不一定要这么做，但是如果您习惯于常规的连接、联合和其他类似的“典型”数据库操作，那么理解这种形式的数据透视就容易多了，所以我推荐您使用它，因为您可能会发现它更易于维护和扩展。执行透视的条件聚合可能更有效，但维护起来更复杂：

WITH X as (
  SELECT
    sku,
    MAX(CASE WHEN properties = 'Family_ID' THEN value END) as family_value,
    MAX(CASE WHEN properties = 'Class_ID' THEN value END) as class_value
  FROM
    table
  GROUP BY sku
)

案件蔓延时 value 根据 properties 价值观。groupby/max然后折叠行，删除空值，留下唯一的sku和指定列中的值（根据它们是哪种值）

--case 1
select *
  from tbl t
where exists (select *
                from tbl t1 
               where t1.sku=t.sku
                 and t1.properties='Family_ID'
                 and t1.value=21)
  and exists (select *
                from tbl t1 
               where t1.sku=t.sku
                 and t1.properties='Class_ID'
                 and t1.value=21)
--case 2
select *
  from tbl t
where exists (select *
                from tbl t1 
               where t1.sku=t.sku
                 and t1.properties='Family_ID'
                 and t1.value=20)
  and exists (select *
                from tbl t1 
               where t1.sku=t.sku
                 and t1.properties='Class_ID'
                 and t1.value=21)