bigquery transpose and concatenate for each record - sql

Question

I want to achieve the following transformation.
I have last_name stored in a repeated record as follows.
data before transformation
I want to achieve the following.
data after transformation
Example with sample data created.
create or replace table t1.cte1 as
WITH t1 AS (
SELECT 1 as id,'eren' AS last_name UNION ALL
SELECT 1 as id,'yilmaz' AS last_name UNION ALL
SELECT 1 as id,'kaya' AS last_name
)
SELECT id,ARRAY_AGG(STRUCT(last_name)) AS last_name_rec
FROM t1
GROUP BY id;
with test as (
select x.id, x.lname_agg,y.last_name from
(
select id, STRING_AGG(h.last_name,' ') lname_agg FROM
t1.cte1
LEFT JOIN
UNNEST(last_name_rec) AS h
group by id
) x,
(select id,h.last_name last_name FROM
t1.cte1
LEFT JOIN
UNNEST(last_name_rec) AS h
group by last_name,id) y
) select id ,sp.string_flatten_dedup( lname_agg,' ') concat_last_name, last_name from test;
I'm not sure either if I should store it as an array instead of a concatenated field but it would be good to know how to achieve both.
storing the concat_last_name as an array
I have achieved the first transformation as follows but I had to dedup the concatenated field with a function I wrote.
I'm sure there is a much better way of achieving this.
with test as (
select x.id id, x.lname_agg,y.last_name from
(
select id, STRING_AGG(h.last_name,' ') lname_agg FROM
small_test
LEFT JOIN
UNNEST(last_name_rec) AS h
group by id
) x,
(select id,h.last_name last_name FROM
small_test
LEFT JOIN
UNNEST(last_name_rec) AS h group by last_name,id) y
) select id ,sp.string_flatten_dedup( lname_agg,' ') concat_last_name, last_name from test;
The function.
string_flatten_dedup
CREATE OR REPLACE FUNCTION
sp.string_flatten_dedup(string_value string,
delim string) AS
(
ARRAY_TO_STRING
(ARRAY(SELECT distinct string_value
FROM UNNEST(SPLIT(string_value, delim)) AS string_value
order by string_value desc, string_value),
delim)
);
before using function.
intermediate results.
Final result after applying dedup function.
final output
Updated table structure.
t1.ccte1
Yours works but I got the table structure incorrect when I first posted.
create or replace table t1.cte2 as
with your_table as (
select 1 id, ['brown', 'smith', 'jones'] last_name union all
select 2, ['ryan', 'murphy']
) select id, ln as last_name,
array_to_string(last_name, ',') as concat_last_name,
from your_table, unnest(last_name) ln;
select id, ln as last_name,
array_to_string(last_name, ',') as concat_last_name,
from t1.cte2, unnest(last_name) ln;
--fails as its not the structure I thought it was cte1 is different then cte2
select id, ln.last_name
--array_to_string(last_name, ',') as concat_last_name,
from t1.cte1, unnest(last_name_rec) ln;

Answer 1

Consider below approach
select id, ln as last_name,
array_to_string(last_name, ',') as concat_last_name,
from your_table, unnest(last_name) ln
if applied to sample data in your question data before transformation
with your_table as (
select 1 id, ['brown', 'smith', 'jones'] last_name union all
select 2, ['ryan', 'murphy']
)
output is
In case if you want last names as an array - you already have this array - see below for how to use it
select id, ln as last_name,
last_name as concat_last_name,
from your_table, unnest(last_name) ln
with output