Contents
Should I use auto increment for primary key?
Auto-increment should be used as a unique key when no unique key already exists about the items you are modelling. So for Elements you could use the Atomic Number or Books the ISBN number.
Is index required on primary key?
Yes a primary key is always an index. If you don’t have any other clustered index on the table, then it’s easy: a clustered index makes a table faster, for every operation. If you don’t have one, it’s quite obvious the DTA would recommend one, and put it on the Primary Key column(s) by default.
When should I use primary key or index?
You always want a primary key on your table, since it’s the only way to identify rows. An index is basically a dictionary for a field or set of fields. When you ask the database to find the record where some field is equal to some specific value, it can look in the dictionary (index) to find the right rows.
Is primary index same as primary key?
A primary key is a column of table which uniquely identifies each tuple (row) in that table. Primary key enforces integrity constraints to the table. Only one primary key is allowed to use in a table….Comparison Chart:
| Parameter | PRIMARY KEY | UNIQUE KEY |
|---|---|---|
| Index | Creates clustered index | Creates non-clustered index |
Is foreign key an index?
MySQL requires that foreign key columns be indexed; if you create a table with a foreign key constraint but no index on a given column, an index is created. Information about foreign keys on InnoDB tables can also be found in the INNODB_FOREIGN and INNODB_FOREIGN_COLS tables, in the INFORMATION_SCHEMA database.
Can a primary key be auto incremented in a database?
The answer to (3) depends on whether you need to generate keys independently from the database (e.g. while disconnected, or while connected to a different database). If yes, you could use GUIDs (which obviously cannot be auto-incremented, but can be uniquely generated in isolation).
When do you not need an auto increment key?
Other cases when a surrogate auto-increment key is not needed: You already have a combination of other columns (whether they are surrogate keys or natural keys) that provides a candidate key for the table. A good example is found in many-to-many tables.
When to use auto increment in a PK?
To have an auto-increment PK makes it easy to create a key that never needs to change, which in turn makes it easy to reference in other tables. If your data is such that you have natural columns that are unique and can never change you can use them just as well.
When to use unique column as primary key?
If table has a unique column, which’s better that set the unique column as primary key or add a new column ‘id’ as auto_increment primary key? If the unique column is also non-nullable, then you can use it as a primary key. Primary keys require that all of their columns are non-nullable.