具有相同表和连接逻辑但结果不同的两个查询

Question

我试图仅在 1 table 中获取记录，即在 A 中而不是在 B 中案例 1：

 select count(distinct t.col1),count(distinct t.col2)
    from `table1` e
    right join
    (
    select distinct col1,col2
    from `table2_*`
    where _table_suffix between '20180101' and '20181231'
    )t
    on e.col1=t.col1
    where date(timestamp_seconds(ts))>='2018-01-01'
    and e.col1 is null
    ;

案例 2：

select count(distinct col1)
from `table2_*`
where _table_suffix between '20180101' and '20181231'
and col1 not in (
select distinct col1 from `table1`
where date(timestamp_seconds(ts))>='2018-01-01'
)

在 2 个代码中，案例 2 有效，而案例 1 输出 0。我还尝试将案例 1 作为左连接与 tables 反转，但结果是相同的 0 行。我是 Big Query 和标准 sql 版本的新手，我不确定为什么会发生这种情况。

Answer 1

Out of the 2 codes, case2 worked while case1 gave 0 as output.

这是因为 NOT IN returns NULL 当列表中有一个 NULL 时。如果您不希望出现这种情况，请排除 NULL 值：

select count(distinct col1)
from `table2_*`
where _table_suffix between '20180101' and '20181231'
and col1 not in (
select distinct col1 from `table1`
where date(timestamp_seconds(ts))>='2018-01-01'
and col1 IS NOT NULL
)

Answer 2

如果使用 NOT IN，您不得允许 NULL 作为 "in list"

的值

SELECT count(DISTINCT t.col1)
FROM `table2_ * ` AS t
WHERE t._table_suffix BETWEEN '20180101' AND '20181231'
 AND col1 NOT IN (
  SELECT DISTINCT e.col1
  FROM `table1` AS e
  WHERE DATE (timestamp_seconds(e.ts)) >= '2018-01-01'
   AND e.col1 IS NOT NULL
  );

我个人更喜欢使用 NOT EXISTS:

SELECT count(DISTINCT t.col1)
FROM `table2_ * ` AS t
WHERE t._table_suffix BETWEEN '20180101' AND '20181231'
 AND NOT EXISTS (
  SELECT NULL
  FROM `table1` AS e
  WHERE DATE (timestamp_seconds(e.ts)) >= '2018-01-01'
   AND e.col1 = t.col1
  );

注意，这里的子查询select子句不需要return任何值，所以select null或select 1或select *都是有效的。使用 exits 或 not exists 时，重要的是子查询的 from & where 子句。

具有相同表和连接逻辑但结果不同的两个查询

Two queries with same tables and join logic but different results

sql

google-bigquery

bigquery-standard-sql