Re: SQL Dummy Needs Help

* Alder <Terrence(dot)Branscombe(at)gems8(dot)gov(dot)bc(dot)ca> menulis:
> I'm pretty new to SQL and can't figure out how to write what should be a
> simple query of two tables. Could someone here possibly help me out?
>
> Table 1 has two fields I'm interested in: TITLE_NO and EFFECT_DATE
> Table 2 also has two fields of interest: TITLE_NO and PAIDTO_DATE
>
> TITLE_NO is unique in Table 1, meaning each TITLE will have a unique
> EFFECT_DATE. Table 2 represents an accounting history of each TITLE, so for
> each TITLE_NO there may be one or more PAIDTO_DATE values. In both Tables
> the _DATE fields are stored as 9-character strings in the fomat YYYYMMDD.

It's probably better to store them as type date instead. That way you
can use functions like date_part() to extract the month and day.

You could use string functions to extract, say, the last 4 characters to
get the MMDD value, but that can get messy if someone accidentally
stores a date in YYMMDD format.

> In all cases, the MM and DD values in Table 2 should be identical with those
> in Table 1.
>
> My intention is to produce a list that will contain the TITLE_NO of each
> TITLE where the MMDD value for EFFECT_DATE differ from any of the
> PAIDTO_DATE values for that TITLE_NO. The list must contain ONLY the
> PAIDTO_DATE values that differ, and the corresponding TITLE_NO.
>
> Sorry I can't explain this a little more technically, but if anyone can
> advise me, that would be fabulous.

If you change your tables to store the dates as type date instead of
type string, then you can do something like the following:

SELECT table2.title_no, table2.paidto_date
FROM table1, table2
WHERE table1.title_no=table2.title_no
AND (date_part('month', table1.effect_date) !=
date_part('month', table2.paidto_date)
OR date_part('day', table1.effect_date) !=
date_part('day', table2.paidto_date));

(At least, I think that will work, but I never trust any SQL I write
without thoroughly testing it first..;)

--
Cliff Crawford

He who sacrifices his conscience to ambition
burns a picture to obtain the ashes. - Chinese proverb