How to get rid of gaps in rowid numbering after deleting rows? - sql

Question

Table tmp :
CREATE TABLE if not exists tmp (
id INTEGER PRIMARY KEY,
name TEXT NOT NULL);
I inserted 5 rows. select rowid,id,name from tmp; :
rowid
id
name
1
1
a
2
2
b
3
3
c
4
4
d
5
5
e
Now I delete rows with id 3 and 4 and run above query again:
rowid
id
name
1
1
a
2
2
b
5
5
e
rowid is not getting reset and leaves holes. Even after vacuum it doesn't reset rowid.
I want :
rowid
id
name
1
1
a
2
2
b
3
5
e
How to achieve above output?

Answer 1

I assume you already know a little about rowid, since you're asking about its interaction with the VACUUM command, but this may be useful information for future readers:
rowid is a special column available in all tables (unless you use WITHOUT ROWID), used internally by sqlite. A VACUUM is supposed to rebuild the table, aiming to reduce fragmentation in the database file, and may change the values of the rowid column. Moving on.
Here's the answer to your question: rowid is really special. So special that if you have an INTEGER PRIMARY KEY, it becomes an alias for the rowid column. From the docs on rowid:
With one exception noted below, if a rowid table has a primary key that consists of a single column and the declared type of that column is "INTEGER" in any mixture of upper and lower case, then the column becomes an alias for the rowid. Such a column is usually referred to as an "integer primary key". A PRIMARY KEY column only becomes an integer primary key if the declared type name is exactly "INTEGER". Other integer type names like "INT" or "BIGINT" or "SHORT INTEGER" or "UNSIGNED INTEGER" causes the primary key column to behave as an ordinary table column with integer affinity and a unique index, not as an alias for the rowid.
This makes your primary key faster than it would've been otherwise (presumably because there's no lookup from your primary key to rowid):
The data for rowid tables is stored as a B-Tree structure containing one entry for each table row, using the rowid value as the key. This means that retrieving or sorting records by rowid is fast. Searching for a record with a specific rowid, or for all records with rowids within a specified range is around twice as fast as a similar search made by specifying any other PRIMARY KEY or indexed value.
Of course, when your primary key is an alias for rowid, it would be terribly inconvenient if this could change. Since rowid is now aliased to your application data, it would not be acceptable for sqlite to change it.
Hence, this little note in the VACUUM docs:
The VACUUM command may change the ROWIDs of entries in any tables that do not have an explicit INTEGER PRIMARY KEY.
If you really really really absolutely need the rowid to change on a VACUUM (I don't see why -- feel free to discuss your reasons in the comments, I may have some suggestions), you can avoid this aliasing behavior. Note that it will decrease the performance of any table lookups using your primary key.
To avoid the aliasing, and degrade your performance, you can use INT instead of INTEGER when defining your key:
A PRIMARY KEY column only becomes an integer primary key if the declared type name is exactly "INTEGER". Other integer type names like "INT" or "BIGINT" or "SHORT INTEGER" or "UNSIGNED INTEGER" causes the primary key column to behave as an ordinary table column with integer affinity and a unique index, not as an alias for the rowid.

Answer 2

I found a solution for some case. I don't know why, but this worked.
1.Rename column "id" to any other name (not PRIMARY KEY) or delete this column because you have already "rowid".
CREATE TABLE if not exists tmp (
my_i INTEGER NOT NULL,
name TEXT NOT NULL);
2.Insert 5 rows in it.
select rowid,* from tmp;
rowid my_i name
1 1 a
2 2 b
3 3 c
4 4 d
5 5 e
3.Delete rows with rowid 3 and 4 and run above query again.
DELETE FROM tmp WHERE rowid = 3;
DELETE FROM tmp WHERE rowid = 4;
select rowid,* from tmp;
rowid my_i name
1 1 a
2 2 b
5 5 e
4.Run SQL
VACUUM;
5.Run SQL
select rowid,* from tmp;
The output:
rowid my_i name
1 1 a
2 2 b
3 5 e

Answer 3

You must define all data from database to new array / list.After that you must delete table and rewrite all data from array / list to database .
Check it ;
https://stackoverflow.com/a/57862686/8363647

Answer 4

I don't get why there is so much hesitance in illustrating the answer here.
If there are any tips or specific examples y'all could provide on how or why or when to be weary of usage, we'd all appreciate it.
Here is how I solved my problem, similar to OP.
c.execute(f"DELETE FROM customers WHERE rowid = ({id})")
print(f"deleted {id}")
conn.commit()
c.execute("VACUUM")
conn.close()