BigQuery：根据字段条件从另一个表追加记录

Question

我想在 BigQuery 中垂直连接两个表，这可以使用 UNION ALL 轻松完成，例如：

 SELECT
      t1.column1, 
      t1.column2, 
      t1.column3
    FROM
      `project.database.table1` as t1
    UNION ALL
    SELECT
      t2.column1, 
      t2.column2, 
      t2.column3
    FROM
      `p21-project.database.table2` as t2

但我想排除 t2 行：

t2.column2=t1.column2 且 t1.column1=X

否则始终追加。

如何实施？

Answer 1

您可以将表 A 与表 B 连接以识别重复的行。

With 
testA as (Select x col1, x+1 col2, "X" colX, "tableA" col3 from unnest([1,2,3,4,5]) as x),
testB as (Select x col1, x+20 col2, "Y", "tableB" from unnest([3,4,8,9]) as x),

tableA_filted as (Select col1 from testA where colX="X" group by 1),

tableB as (
  Select B.* from testB as B
  left join tableA_filted as A
  on A.col1=B.col1
  where A.col1 is null
)


SELECT * from testA
Union ALL
SELECT * from tableB

由于您知道并非完整的表 A 相关，因此过滤此表并仅保留

tableA_filted

中的相关列。

group by 1

可防止重复输入。然后将其左连接到表 B，并仅保留此连接失败的行。

对于许多场景，

full join

是比

union all

更好的解决方案。