组合 MySQL 表中的 2 列以创建具有特定字符串的新列

Question

I have the following columns in my table:

launch_month    Years   
Jun             2018    
July            2018    
Aug             2018

I want to create a new column called 'launch_id' and combine the other 2 columns into a string of '201806', so the above would look like:

launch_month    Years   launch_id
Jun             2018    201806
July            2018    201807
Aug             2018    201808

Can anyone help?

Answer 1

One option uses a case expression:

select
    launch_month,
    years,
    years * 100 + case launch_month
        when 'Jan' then  1
        when 'Feb' then  2
        when 'Mar' then  3
        ...
        when 'Dec' then 12
    end launch_id
from mytable

This generates a new numeric column called launch_id , that represents the date in format YYYYMM .

Alternatively, you can use date functions (but this might be less efficient):

select 
    launch_month,
    years,
    date_format(
        str_to_date(concat('01', launch_month, years), '%d%b%Y'),
        '%Y%m'
    ) launch_id
from mytable

This generates a string result. If you want a number, you can just convert it, either explicitly ( cast() ) or implicitly ( + 0 ).