what is the use of primary and foriegn keys?

aditya immadi

10y880

Hi All,

i have confusing little here..what is the actual use of foriegn key an primary key relations .can we bind the date using this relation only...if we want records from both tables which contains PK andFK relation any way we use joins .then what is actuall use of these. can any one explain me with real time example

3 Replies

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Nitin Sontakke10y ago
I understand your confusion. You are saying if I can get data from joining the keys what bother defining the keys.
However, as Francis already mentioned, PK and FK work as a constraints. Meaning, you cannot insertNULL in a PK column and you cannot insert duplicate value in PK column. Similarly, while you can insert NULL in FK column (if it is nullable) you cannot insert a value in a FKcolumn which is not present in PK column in another table to which FK column references.
For example, if youhave appropriately definedPK and FK,you cannot insert a ProductId in a InvoiceItem table if ProductId is not present in Product Master table. Simple.
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kalu singh rao10y ago
You can read below link of microsoft where you get full description about primary keys and foreign keys in database.

Table have only one primary key but it have multiple foreign keys. Keys are used for maintain relationship between multiple tables of database.

https://msdn.microsoft.com/en-IN/library/ms179610.aspx
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Francis Susaimichael10y ago
In real time, what is the relationship abouta boy andanother man in the same family? Can you guess it. Nope. because it may be Son & father orgrandson& father etc.So the "relationship" definesit. So you name it at least to define. This is where the "relationship" will come. Normally a primary key, isavailable inside a Table. If you want to relate the 2 tables Foreign key comesto picture.
Primary and foreign keys are not only used to define the relationship between the tables.More than that,they giveconstraints to the inserted data. In another way "data consistency" will be another advantage of these keys.
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