我想填充 BigQuery 表数据中有漏洞的行

Question

What we want to solve

We have never worked much with DWH or sql and don't know how to do it... Can someone please help us?

We want to fill in the missing rows in the BigQuery table data.

Current situation: I have written daily business data in BigQuery like the following master data. I would like to overwrite the blank rows in the "male" column, but I don't know what is the best way to do it.

The table is about 20000 rows.

I have a separate table for employee rosters that is linked to the table I want to rewrite by id, so I thought it would be better to use that, but I am having trouble getting to it...

Problem/error

-Master data
date       id   name gender task
2022-08-01 0001 Jack        projectA
2022-08-02 0001 Jack  male  projectA
2022-08-03 0001 Jack        projectA
2022-08-04 0001 Jack  male  projectB
2022-08-05 0001 Jack        projectB
2022-08-01 0002 Smith male  projectA
2022-08-02 0003 Smith       projectB
2022-08-03 0004 Smith male  projectB

-Employee Roster Table
id   name     gender 
0001 Jack     male
0002 Smith    male
0003 Paul     male
0004 Naomi    Female

Translated with www.DeepL.com/Translator (free version)

Answer 1

Assuming IDs in the employee roster table are unique, you can use a JOIN operation

If you want to overwrite the gender column altogether with the roster data the query would look something like

select
  main.date,
  main.id,
  main.name
  roster.gender
  main.task
from main_table as main
left join employee_roster_table as roster on main.id = roster.id

If you want to keep the gender that are filled in the main table and only use the roster's when null you can use

select
  main.date,
  main.id,
  main.name
  coalesce(main.gender, roster.gender) as gender
  main.task
from main_table as main
left join employee_roster_table as roster on main.id = roster.id