IF with timestamp bigquery-CodePudding

I need to add an attribute that indicates if that version is an original or copy. If is the first version of the site, is original, it is not, is a copy.

the table:

id_site  id_version timestamp_version
1        5589       2/3/2022
1        2030       10/7/2022
1        1560       10/8/2022
2        6748       2/3/2022
2        7890       2/4/2022
3        4532       2/3/2022

The expected result:

id_site id_version  timestamp_version   type_version
1       5589        2/3/2022            original
1       2030        10/7/2022           copy
1       1560        10/8/2022           copy
2       6748        2/3/2022            original
2       7890        2/4/2022            copy
3       4532        2/3/2022            original

CodePudding user response：

You can use an IF or CASE here. They are mostly interchangeable, but my preference is CASE since it's portable to nearly any other RDBMS where IF is only supported in a few.

 CASE WHEN ROW_NUMBER() OVER (PARTITION BY id_site ORDER BY timestamp_version ASC) = 1 THEN 'copy' ELSE 'original' END

Inside the CASE expression we do a ROW_NUMBER() window function will "window" or partition each row in the result set by id_site and number each record for each distinct id_site sequentially ordered by timestamp_version in ascending order. We test to see if that ROW_NUMBER() is 1 and then label it with original or copy.

CodePudding user response：

You can use a window function in an if statement for that:

with test as (

    select * from unnest([
        struct(1 as id_site, 5589 as id_version, timestamp(date "2022-03-02") as timestamp_version),               
            (1, 2030, timestamp(date "2022-07-10")),
            (1, 1560, timestamp(date "2022-08-10")),
            (2, 6748, timestamp(date "2022-03-02")),
            (2, 7890, timestamp(date "2022-04-02")),
            (3, 4532, timestamp(date "2022-03-02"))
    ])
)

select 
    *,
    IF(timestamp_version = min(timestamp_version) over (partition by id_site), "original", "copy") AS type_version 
from test

CodePudding user response：

Consider below option

select *,
  if(lag(id_version) over prev is null, 'original', 'copy') type_version,
from your_table
window prev as (partition by id_site order by timestamp_version)

if applied to sample data in your question - output is