Original problem: What is the right column format for a unix timestamp?
The net is full of confusion: some posts claim SQLite has no unsigned types - either whatsoever, or with exception of the 64bit int type (but there are (counter-)examples that invoke UNSIGNED INTEGER). The data types page mentions it only in a bigint example. It also claims there is a 6-byte integer but doesn't give a name for it. It seems my tries with INTEGER being 4-byte signed signed store unix timestamps as negative numbers. I've heard that some systems return 64-bit timestamps too. OTOH I'm not too fond of wasting 4 bytes to store 1 extra bit (top bit of timestamp), and even if I have to pick a bigger data format, I'd rather go for the 6-byte one. I've even seen a post that claims SQLite unix timestamp is of type REAL...
Complete problem: Could someone please clarify that mess?
The size of an integer
All columns in SQLite databases are internally variable-width. The file format stores integers in 1, 2, 3, 4, 6, or 8 bytes, depending on how big the number is, plus one byte in the header to indicate the size. So, in total, Unix dates stored as integers will take up 5 bytes until 2038-01-19 and 7 bytes after that.
From the point of view of the user of the C API, all integers are signed 64-bit.
The column type
It doesn't matter whether you declare your column as INTEGER, UNSIGNED INTEGER, BIGINT, or whatever. Anything with "INT" in it has integer affinity. And, as mentioned above, all integers are signed 64-bit but not usually stored that way.