Question

I am trying to join two tables using mysql, this is not difficult, my problem is the column I am joining on has a nonstandard type, I am joining on the birthday column which can come in a variety of different styles:

10/29
01/10/1984
12/32/2007
10/1997
null
1984

I only want to join the columns if the users are from the same year, so in the above example

01/10/1984
1984

Would be allowed for a join, while the others would be ignored.

Does mysql offer a way to split the birthdays into just their year components?

Answer 1

You could may be join using the RIGHT()function, to join on only the last 4 digits of the date, and also use INSTR() to check that the last 4 digits do not contain ‘/’ (ie making sure it is a year).

Something like this:

SELECT 
    *
FROM 
    tbl1 t
JOIN tbl2 ON (RIGHT(tbl1.colname, 4) = RIGHT(tbl2.colname, 4) AND INSTR(RIGHT(tbl1.colname, 4), '/') = 0)

This relies on the fact that the year is always the last four digits of the field.