Table without a primary key.
I'm currently scripting this database from MsSQL to MySQL and have come across this table that has no primary key. Now this is just out of curiosity, I don't have a lot of SQL experience but from what I have been thought: Every table needs a primary key.
I guess my question is: Would there be any time or situation where one would need to create a table without a primary key?
You can create tables in MySQL without a primary key. You normally only do this when a table is acting as a 'go-between' of two tables and a unique identifier is not required or useful. For example, if a person adds a property to their favourites, then there could be a table which has the following fields - personIDfk, propertyIDfk, date_added - which has the effect of linking the person with the property and no primary key is required or useful.
Originally Posted by GreenMushroom16
That makes sense, although the table I have come across holds these fields:
I guess it's used to locate available applications, my guess is this table would need a key if they ever need to add another table giving properties to this one. Maybe they'll never need to but I just think it would be good practice to add a key anyways.
Note that a primary key can be across mutliple columns, so if in this example some combination of 2 or 3 columns should never be duplicated, you might make that combination the primary key (PCName and AppPath, perhaps?).
"Please give us a simple answer, so that we don't have to think, because if we think, we might find answers that don't fit the way we want the world to be."
~ Terry Pratchett in Nation
As stated, you don't need a PK and/or your PK can span columns. However, best practice is to use an auto_inc PK (even if you're using UUIDs) on every table. This is particularly important in web development, particularly because most of your tables will/ought be InnoDB.
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