Here are my sqlite db details,
sqlite> .table
url_db
sqlite> .schema url_db
CREATE TABLE url_db(URL TEXT UNIQUE);
sqlite> select * from url_db;
play.googleapis.com
notifications.google.com
contacts.skype.com
edge.skype.com
people.skype.com
I wanted to execute the command delete from url_db limit 1
.
So I've downloaded the full source code (sqlite-src-3240000.zip) from the official download page .
Compiled the source code with the option 'SQLITE_ENABLE_UPDATE_DELETE_LIMIT=1'
When I execute that command (command executed), sometimes it deletes the random entry but not the first entry. I wanted to delete play.googleapis.com
, instead that command deleted contacts.skype.com
.
sqlite> select * from url_db;
play.googleapis.com
notifications.google.com
edge.skype.com
people.skype.com
What's the cause for this behavior? I am implementing a FIFO list in which when the entries reach 500, I need to delete the first entry.
sometimes it deletes the random entry but not the first entry.
You misunderstand relational databases. A table represents an unordered set. There is no "first" row in a table, unless you explicitly define the ordering.
Because this problem occurs so often, SQLite has a built-in work-around, the rowid
"column". You can use this as a regular column, resulting in:
delete from url_db
order by rowid
limit 1;
Personally, I prefer an explicitly declared auto-increment column, but SQLite builds in this functions (unlike other databases).
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