Hot answers tagged database-design
3
It depends very much on the DBMS being used. Some can never user more than one index per table and query other can do so.
But if there are multiple indexes sharing the same column, I doubt that even the DBMS that can use more than one index would do it, especially if the leading columns are identical.
If there is an index on (foo) and one on (foo, bar) ...
3
This is no single answer
The optimiser will choose an index that best suits the predicates of the query.
This depends on
statistics/selectivity
index key order and includes/covering
number of predicates
You may also have index intersection or key lookups where 2 or more indexes are used
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You can use MySQL Workbench to connect and migrate your schema/data from MS Access to mySQL.
First you need to configure an ODBC Data Source:
Click Start, and then click Control Panel.
In the Control Panel, double-click Administrative Tools.
In the Administrative Tools dialog box, double-click Data Sources (ODBC). The ODBC Data Source Administrator dialog ...
1
If it's a table of 3 columns, you're probably overthinking this. Strict 3NF is all well and good, but when you're talking about possibly having two tables just to follow it precisely, it's time to step away from the table, nobody's getting hurt here...
The intent of 3NF is that each table should contain unique keys, and all of the columns should describe ...
1
Relational databases are not built to handle this situation perfectly. You have to decide what is most important to you and then make your trade-offs. You have several goals:
Maintain third normal form
Maintain referential integrity
Maintain the constraint that each account belongs to either a corporation or a natural person.
Preserve the ability to ...
1
I don't have any insider knowledge of how Google Docs is implemented. However, if you look at things like Windows file permissions, this type of thing usually works on the these principles:
Inheritance - To grant access to many objects with the same scope, grant the access at the highest level (e.g. folder, not file) and all children of the granted node ...
1
Some great answers here, and at the risk of repeating other thoughts:
SSN is not necessarily unique. Heck, SSN is not even always known, and in some cases it doesn't exist (yet). SSNs can be reused and not all employees or students may ever have an SSN. This is peripheral to the question but demonstrates that, no matter where you enforce your constraints, ...
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