47. UNIQUE KEY in SQL (Hindi) 

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Even if there is only one NULL you can't identify that particular row becoz NULL contain some unknown value. I can understand your situation as well i m very impressed by your question. I cant believe that i forgot to discuss this part in this series. OK Let's talk about NULL what do you think about NULL i mean according to you what is NULL ? It seems you are taking NULL as string but NULL is something which doesn't really exists or we can't imagine what it could be or an unknown value. So Let's see this example there are two unknown person can u tell both these are same guy or different ? NO, You can't tell becoz you don't know them this is what NULL is. NULL (first unknown person) and NULL (2nd unknown person) it means NULL is not equal to NULL in SQL. I hope it is clear to you ?

Geeky Shows k I know the functionality of NULL but as like primary key doesn't accept duplicate we have to give auto_constraint to it without which error appear similarly we should give auto_contraint to this also naaa ...... As the only difference between primary key n unique key is PK don't accept NULL values n UK accept it

There is one more difference there can be only one PRIMARY KEY in a table while UNIQUE KEY may be more than one. Trust me you will understand the genuine use of UK and PK when you will do some real project for now i believe your concept has clear.

Nothing.no errors as no duplicates

Yes unique key will allow everything of its type but wont allow the duplicate but null is not equal to null so we can add multiple nulls

@@darknightcore9905 that's a lot of null xD

suppose you have to fetch details by adhar card then adhar card number can me made unique - primary key is just auto-increment number.

@@binodthakur6113 thanks for solved my confusion and also thanks for ur quick response😃

Multiple primary key defined. One table can have only one Primary Key.

Yes, already mentioned in the video.

@@debarghyachakraborty dude you are replying like a year later. I don't really care about that at this point lol

Desc gives you the meta data where as select helps in retrieving the information

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Primary key can be only one. Unique key can be multiple.

@@debarghyachakraborty thx