When the database format is 2 or higher (explicitly via "PRAGMA
legacy_file_format = false;" or implicitly via "ALTER TABLE ... ADD COLUMN
..."), sqlite doesn't currently take advantage of the fact that NULL columns at
the end don't have to be stored.
For example:
> PRAGMA legacy_file_format = false;
> CREATE TABLE test (n1,n2,n3,...,n500);
> INSERT INTO test(n1) VALUES('first');
> INSERT INTO test(n1) VALUES('second');
...
> INSERT INTO test(n1) VALUES('twentieth');
Takes a lot more space than:
> CREATE TABLE test (n1);
> INSERT INTO test(n1) VALUES('first');
> INSERT INTO test(n1) VALUES('second');
...
> INSERT INTO test(n1) VALUES('twentieth');
> ALTER TABLE test ADD COLUMN n2;
> ALTER TABLE test ADD COLUMN n3;
...
> ALTER TABLE test ADD COLUMN n500;
Even though the resulting databases are the same, and even if VACUUM is
performed.
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