如何内部连接两个表？

Question

Hi ! Anyone can tell me what's wrong with my jointure? Thank you very much!

SELECT 
country_code,
country_name,
year,
crude_birth_rate,
crude_death_rate

FROM `bigquery-public-data.census_bureau_international.country_names_area`as Country_name_area
INNER JOIN `bigquery-public-data.census_bureau_international.birth_death_growth_rates` as birth_death_growth_rates

ON birth_death_growth_rates.country_code = Country_name_area.country_code;

Answer 1

Refer columns with alias of tables:

SELECT 
Country_name_area.country_code,
Country_name_area.country_name,
birth_death_growth_rates.year,
birth_death_growth_rates.crude_birth_rate,
birth_death_growth_rates.crude_death_rate

FROM `bigquery-public-data.census_bureau_international.country_names_area`as Country_name_area
INNER JOIN `bigquery-public-data.census_bureau_international.birth_death_growth_rates` as birth_death_growth_rates

ON birth_death_growth_rates.country_code = Country_name_area.country_code;

Answer 2

Try this :

1. You have to add alias for table & use into select column statements and join.

Answer 3

When you run the query, the error message is pretty clear:

Error: Column name country_code is ambiguous at [2:1]

You should learn to read the error messages; BQ is pretty good at explaining issues in queries.

The column country_code is in both tables. As mentioned in other answers, you want to qualify all column references. I want to point out that simpler table aliases makes the query easier to write and read.

You can also use USING , because the JOIN keys have the same name:

SELECT country_code, cna.country_name, bdgr.year,
       bdgr.crude_birth_rate, bdgr.crude_death_rate
FROM `bigquery-public-data.census_bureau_international.country_names_area` cna JOIN
     `bigquery-public-data.census_bureau_international.birth_death_growth_rates` bdgr
     USING (country_code);