Is this SQL databases or No-SQL?
Is this SQL databases or No-SQL?
Posted Mar 28, 2014 8:31 UTC (Fri) by cladisch (✭ supporter ✭, #50193)In reply to: Is this SQL databases or No-SQL? by Wol
Parent article: A discussion between database and kernel developers
> If I don't have an index I'll have to scan the entire table - so my worst case is equal to yours (if I'm being stupid!) But all I've got to do is declare an index on the invoice no ... and it takes one disk read (97% probability) to convert from invoice no to invoice key, and one more to retrieve the invoice.
Most relational databases (even SQLite) can store table rows ordered by their primary key (typically called "index-organized" or "clustered" tables), so no separate index lookup would be required.
> When making my claims about RDBMSs, I'm mostly speculating. You see, I'm *not* *allowed* to know what's going on under the covers, so I'm forced to guess.
Nobody forbids you to find out what's going on under the covers. Most relational database document low-level details (or even their file format) to allow manual optimizations.