I need help counting char occurencies in a row with sql (using firebird server) - sql

Question

I have a table where I have these fields:
id(primary key, auto increment)
car registration number
car model
garage id
and 31 fields for each day of the mont for each row.
In these fields I have char of 1 or 2 characters representing car status on that date. I need to make a query to get number of each possibility for that day, field of any day could have values: D, I, R, TA, RZ, BV and LR.
I need to count in each row, amount of each value in that row.
Like how many I , how many D and so on. And this for every row in table.
What best approach would be here? Also maybe there is better way then having field in database table for each day because it makes over 30 fields obviously.

Answer 1

There is a better way. You should structure the data so you have another table, with rows such as:
CarId
Date
Status
Then your query would simply be:
select status, count(*)
from CarStatuses
where date >= #month_start and date < month_end
group by status;
For your data model, this is much harder to deal with. You can do something like this:
select status, count(*)
from ((select status_01 as status
from t
) union all
(select status_02
from t
) union all
. . .
(select status_31
from t
)
) s
group by status;

Answer 2

You seem to have to start with most basic tutorials about relational databases and SQL design. Some classic works like "Martin Gruber - Understanding SQL" may help. Or others. ATM you miss the basics.
Few hints.
Documents that you print for user or receive from user do not represent your internal data structures. They are created/parsed for that very purpose machine-to-human interface. Inside your program should structure the data for easy of storing/processing.
You have to add a "dictionary table" for the statuses.
ID / abbreviation / human-readable description
You may have a "business rule" that from "R" status you can transition to either "D" status or to "BV" status, but not to any other. In other words you better draft the possible status transitions "directed graph". You would keep it in extra columns of that dictionary table or in one more specialized helper table. Dictionary of transitions for the dictionary of possible statuses.
Your paper blank combines in the same row both totals and per-day detailisation. That is easy for human to look upon, but for computer that in a sense violates single responsibility principle. Row should either be responsible for primary record or for derived total calculation. You better have two tables - one for primary day by day records and another for per-month total summing up.
Bonus point would be that when you would change values in the primary data table you may ask server to automatically recalculate the corresponding month totals. Read about SQL triggers.
Also your triggers may check if the new state properly transits from the previous day state, as described in the "business rules". They would also maybe have to check there is not gaps between day. If there is a record for "march 03" and there is inserted a new the record for "march 05" then a record for "march 04" should exists, or the server would prohibit adding such a row. Well, maybe not, that is dependent upon you business processes. The general idea is that server should reject storing any data that is not valid and server can know it.
you per-date and per-month tables should have proper UNIQUE CONSTRAINTs prohibiting entering duplicate rows. It also means the former should have DATE-type column and the latter should either have month and year INTEGER-type columns or have a DATE-type column with the day part in it always being "1" - you would want a CHECK CONSTRAINT for it.
If your company has some registry of cars (and probably it does, it is not looking like those car were driven in by random one-time customers driving by) you have to introduce a dictionary table of cars. Integer ID (PK), registration plate, engine factory number, vagon factory number, colour and whatever else.
The per-month totals table would not have many columns per every status. It would instead have a special row for every status! The structure would probably be like that: Month / Year / ID of car in the registry / ID of status in the dictionary / count. All columns would be integer type (some may be SmallInt or BigInt, but that is minor nuancing). All the columns together (without count column) should constitute a UNIQUE CONSTRAINT or even better a "compound" Primary Key. Adding a special dedicated PK column here in the totaling table seems redundant to me.
Consequently, your per-day and per-month tables would not have literal (textual and immediate) data for status and car id. Instead they would have integer IDs referencing proper records in the corresponding cars dictionary and status dictionary tables. That you would code as FOREIGN KEY.
Remember the rule of thumb: it is easy to add/delete a row to any table but quite hard to add/delete a column.
With design like yours, column-oriented, what would happen if next year the boss would introduce some more statuses? you would have to redesign the table, the program in many points and so on.
With the rows-oriented design you would just have to add one row in the statuses dictionary and maybe few rows to transition rules dictionary, and the rest works without any change.
That way you would not