How to unnest an integer array represented as a BLOB? - sqlite

Question

SQLite doesn’t have native support for arrays. I would think that my method (thinking outlined below) of making a custom BLOB encoding would be a fairly common workaround (yes, I need an array rather than normalizing the table). The benefit of representing an integer array as a BLOB is primarily the space savings, for example:
13,24,455,23,64789
Stored as TEXT will take up 18 bytes (commas included, making assumptions here). But if one were to store the above TEXT in a custom encoded BLOB format it would look like this:
0x000D001801C7FD15
Where every number is assumed to take up 2 Bytes (0 to 65,535 or 0000 to FFFF). This BLOB, to my understanding, would then be 10 Bytes. This is nearly half the size as storing it in a delimited TEXT format. This space savings would also be magnified by the number of rows and the number of integers in the array.
Is there a good way of unnesting a BLOB by width? Say that I want to unnest the BLOB so that each row represents an integer. Can I take the above BLOB and turn it into this?
id
number
1
000D
2
0018
3
01C7
4
FD15

Answer 1

SQLite's HEX() function
interprets its argument as a BLOB and returns a string which is the
upper-case hexadecimal rendering of the content of that blob.
After you get the blob as a string use SUBSTR() to slice it in 4 char parts:
WITH cte(id) AS (VALUES (1), (2), (3), (4), (5))
SELECT HEX(t.col) hex_col,
c.id,
SUBSTR(HEX(t.col), (c.id - 1) * 4 + 1, 4) number
FROM tablename t JOIN cte c
ORDER BY t.rowid, c.id;
Or, with a recursive CTE to generate dynamically the list of values 1..n:
WITH cte(id) AS (
SELECT 1
UNION ALL
SELECT id + 1
FROM cte
WHERE id < 5
)
SELECT HEX(t.col) hex_col,
c.id,
SUBSTR(HEX(t.col), (c.id - 1) * 4 + 1, 4) number
FROM tablename t JOIN cte c
ORDER BY t.rowid, c.id;
Change col to the name of your blob column.
See the demo.