Two different date types in column - mysql

Question

I am trying to create a age group array in mysql.
SELECT
COUNT(*),
CASE
when age < 60 THEN '<60'
when age >= 61 AND age <= 65 then '61-65'
when age >= 66 AND age <= 70 then '66-70'
when age >= 71 AND age <= 75 then '71-75'
when age >= 76 AND age <= 80 then '76-80'
when age > 81 then '>81'
END as age_group
FROM(
SELECT YEAR(current_time()) - Year(DateBorn) AS age
FROM custs
WHERE FDID = 'ANGL01'
) as custs2
GROUP BY age_group
When i ran this query, it worked fine, except that there were 2013 null results. It turns out that there are 2 data formats in the column.
The first on is just the year: 'yyyy'
The second on includes the day and month: 'dd/mm/yyyy'
How can I modify this query to take both data formats into account?

Answer 1

Ideally you should store dates using the DATE data type.
Given your current schema, assuming the dates are always either in yyyy or dd/mm/yyyy format then the year will always be the 4 rightmost characters, so you can use RIGHT(DateBorn,4), like this:
SELECT
COUNT(*),
CASE
when age < 60 THEN '<60'
when age >= 61 AND age <= 65 then '61-65'
when age >= 66 AND age <= 70 then '66-70'
when age >= 71 AND age <= 75 then '71-75'
when age >= 76 AND age <= 80 then '76-80'
when age > 81 then '>81'
END as age_group
FROM(
SELECT YEAR(current_date()) - CAST(RIGHT(DateBorn,4) AS UNSIGNED) AS age
FROM custs
WHERE FDID = 'ANGL01'
) as custs2
GROUP BY age_group
You should check for values that don't match your expected date formats. A query like this will give you a sample of non-conformant rows:
select DateBorn
from custs
where DateBorn not regexp '^[0-9][0-9][0-9][0-9]$'
and DateBorn not regexp '^[0-3][0-9]\/[0-1][0-9]\/[0-9][0-9][0-9][0-9]$'
limit 25

Answer 2

How about MySQL's STR_TO_DATE?
SELECT STR_TO_DATE(DATE_FORMAT(YourField, '%d/%m/%Y'),'%Y')...
http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_str-to-date
Using this you can manipulate other occurrences. I have inherited legacy data you cannot change, so this function will accommodate everything you can mask, if your data is fairly consistent.
I may have it backwards. Try this, if needed.
SELECT date_format( str_to_date( dt3, '%m-%d-%Y' ) , '%m/%d/%Y' ) AS my_date FROM dt_tb3
http://www.plus2net.com/sql_tutorial/date-string.php

Answer 3

Assuming that DateBorn is a text column, try this:
SELECT YEAR(now()) - Year(str_to_date(DateBorn,
CASE WHEN char_length(DateBorn) = 4
THEN '01/01/%Y'
ELSE '%d/%m/%Y'
END
)) AS age

Answer 4

current_time() is an alias for curtime() which returns HH:MM:SS. So YEAR(current_time()) may result in some odd results. You might want to try YEAR(NOW()) instead.
You would also want to use STR_TO_DATE(str,format) to parse your varchar as a datetime. (Of course, it is better to fix the schema than patch it like this) Make sure to update the format as you have it in your table.
SELECT
COUNT(*),
CASE
when age < 60 THEN '<60'
when age >= 61 AND age <= 65 then '61-65'
when age >= 66 AND age <= 70 then '66-70'
when age >= 71 AND age <= 75 then '71-75'
when age >= 76 AND age <= 80 then '76-80'
when age > 81 then '>81'
END as age_group
FROM(
SELECT YEAR(NOW()) - Year(str_to_date(DateBorn, '%d/%m/%Y')) AS age
FROM custs
WHERE FDID = 'ANGL01'
) as custs2
GROUP BY age_group