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Should a lookup table have a primary key?
2 Answers. There should be a unique key for (car_idcar, item_list_iditem_list) , but it doesn’t necessarily have to be the primary key. This way, you ensure that you don’t create duplicate relationships between the same rows in the two tables.
What is the primary use of look up table?
It can be used to translate encoded information into a user-friendly description, to validate input values by matching them to a list of valid items, or to translate a shorthand entry into something more detailed. A lookup action retrieves values from a related table.
Why should we use the primary key in a relation table?
Every table can have (but does not have to have) a primary key. The column or columns defined as the primary key ensure uniqueness in the table; no two rows can have the same key. The primary key of one table may also help to identify records in other tables, and be part of the second table’s primary key.
Why do we need look up table?
In data analysis applications, such as image processing, a lookup table (LUT) is used to transform the input data into a more desirable output format. A classic example of reducing run-time computations using lookup tables is to obtain the result of a trigonometry calculation, such as the sine of a value.
Why do you use an int in a lookup table?
One of the reasons I always use is that if someone has misspelled a value in the lookup table, say Oraneg instead of Orange, it is far easy to change the value in the lookup table. The lookup table with a number primary key will only require the value to be changed in the lookup table.
When to change the primary key in a lookup table?
The lookup table with a number primary key will only require the value to be changed in the lookup table. The lookup table using the values as their primary key will need to be changed in the lookup table and in every record in the main table where it was used.
When to use an ID field in a table?
If you want to lookup your data, you really want to do this based on an integer field or fields. This is why many people use an ID field for this. But if you have a table you use for a many-to-many relation, it isn’t really needed. Lets say you have the following two tables:
Why do you use one primary key in SQL?
While compound keys work, a single primary key can be sometimes be easier to work with. For instance, on doing deletes it is very easy to single out a particular row. It is also often more efficient to search on a numeric key. Because ID is used to identify everything.