set a date column in sql based on a another column

Question

So I have a SQL Table with two columns:

Col1      Col2
202205    NULL
202204    NULL
202103    NULL

Now I want to set the Date in Col2 based on the value of Col1. So the result should look like this:

Col1    Col2
202205  2022-05-01
202204  2022-04-01
202103  2021-03-01

Answer 1

Assuming that Col1 be text, we can try using the TO_DATE function here:

WITH yourTable AS (
    SELECT '202205' AS Col1
)

SELECT TO_DATE(Col1 || '01', 'YYYYMMDD') AS Col2  -- 2022-05-01
FROM yourTable;

Answer 2

MySQL:

UPDATE  test_tbl
SET Col2 = STR_TO_DATE(CONCAT(Col1,'','01') ,'%Y%m%d');

db-fiddle

Answer 3

create or replace table Conv(col1 number,col2 number);

insert into Conv values (202205,NULL),(202204,NULL),(202103,NULL);

select Col1,TO_DATE(Col1 || '01', 'YYYYMMDD') AS Col2 from Conv;