Filtering Columns in PLSQL - sql

Question

I have a table with tons and tons of columns and I'm trying to select only certain columns based on the data the columns contain. The table is part of an application I'm building in Oracle APEX and looks something like this:
|Row Header|Criteria 1|Criteria 2| Criteria 3 | Criteria 4 |Criteria 5 |
|Category | Type A | Type B | Type B | Type A | Type A |
| ID | 2.3 | 2.4 | 2.5 | 3.1 | 3.2 |
| Part A | Yes | Yes | Yes | No | Yes |
| Part B | Yes | No | Yes | Yes | Yes |
| Part C | No | Yes | Yes | Yes | No |
It goes on like this for around 1000ish criteria and 100ish parts I need to find a way to select all the columns that are of a specific type to its own table using SQL.
Id Like the return to look like this:
|Row Header|Criteria 1|Criteria 5 |
|Category | Type A | Type A |
| ID | 3.1 | 3.2 |
| Part A | No | Yes |
| Part B | Yes | Yes |
| Part C | Yes | No |
This way I only have the columns showing that are part of the "Type A" Category and have an ID greater than 3.
I've looked into GROUP BY and FILTER functions that SQL has to offer as well as PIVOT and I don't believe these will help me, but I'd be happy to be proven wrong.

Answer 1

In a relational database, columns are meant to be discrete, non-repeating attributes of a thing. Rows are meant to be multiple instances of that thing. Your table is reversed, using columns for what should be rows, and rows for what should be columns. Another factor is that Oracle limits you to 1000 columns, and you start undergoing severe performance degradation when you exceed 254 columns. Tables simply weren't meant to have hundreds, let alone thousands, of columns. So first step is to pivot your table like this:
Criteria_No, Cat, ID, PtA, PtB, PtC
---------------------------------------------
Row 1: Criteria 1, Type A, 2.3, Yes, Yes, No
Row 2: Criteria 2, Type B, 2.4, Yes, No, Yes
Row 3: Criteria 3, Type B, 2.5, Yes, Yes, Yes
. . . thousands more
But even then, you mentioned that you have 100s of "parts", so Parts A, B, C aren't the only three - the series continues. If so, it would be a violation of normal form to have such a repeating list in a single row. So you have one more step to fix your design: Break this into three tables.
CRITERIA
Criteria_No, Cat, ID
---------------------------------------------
Row 1: Criteria 1, Type A, 2.3
Row 2: Criteria 2, Type B, 2.4
Row 3: Criteria 3, Type B, 2.5
PARTS
Part, anything-else-about-part
-----------------
Part A, blah
Part B, blah,
Part C, blah
. . .
And now the bridge table between them:
CRITERIA_PARTS
Criteria_No, Part
-----------------
1, Part A
1, Part B
1, Part C
2, Part A,
2, Part B,
. . . and so on
You should also place a foreign key on each of the bridge table columns to point to their respective parent tables to ensure data integrity.
Now you query by joining the tables together in your SQL.
Updated: you asked how to move data into this new criteria table from your existing one. Use dynamic SQL like this:
BEGIN
FOR i IN 1..1000
LOOP
EXECUTE IMMEDIATE 'INSERT INTO criteria (criteria_no,cat,id) SELECT criteria_'||i||',category,id FROM oldtable';
END LOOP;
COMMIT;
END;
But of course set the 1000 to the real # of category_n columns.