Question

I have a date of birth DATE column in a customer table with ~13 million rows. I would like to query this table to find all customers who were born on a certain month and day of that month, but any year.

Can I do this by casting the date into a char and doing a subscript query on the cast, or should I create an aditional char column, update it to hold just the month and day, or create three new integer columns to hold month, day and year, respectively?

This will be a very frequently used query criteria…

EDIT:… and the table has ~13 million rows.

Can you please provide an example of your best solution?

Answer 1

If it will be frequently used, consider a ‘functional index’. Searching on that term at the Informix 11.70 InfoCentre produces a number of relevant hits.

You can use:

WHERE MONTH(date_col) = 12 AND DAY(date_col) = 25;

You can also play games such as:

WHERE MONTH(date_col) * 100 + DAY(date_col) = 1225;

This might be more suitable for a functional index, but isn’t as clear for everyday use. You could easily write a stored procedure too:

Note that in the absence of a functional index, invoking functions on a column in the criterion means that an index is unlikely to be used.

CREATE FUNCTION mmdd(date_val DATE DEFAULT TODAY) RETURNING SMALLINT AS mmdd;
    RETURN MONTH(date_val) * 100 + DAY(date_val);
END FUNCTION;

And use it as:

WHERE mmdd(date_col) = 1225;