Types Of Keys | Data Base Management System By Technical UA
Good day all and sundry in this article we will be discussing approximately database management systems and the contemporary subject matter is types of keys so we'll be going through all the varieties of keys and DBMS and we'll be differentiating the keys how the only key isn't like different and while the unique key is used.
Types Of Keys :
1 : Number one Key
First sort of key is a primary key. all of us comprehend it truly all of us have heard approximately it all of us have studied about it so just a revision of all of the keys so the number one key set of one or extra attributes so it may be a single attribute or it may be a set of attributes of a relation that uniquely become aware of take into account any database for instance assume we have a student database so which attribute the databases scholar so which characteristic of the pupil would uniquely identify the scholar it would be both the roll quantity or the registration wide variety so the roll quantity would be the primary key or the registration number will be the number one key a unmarried scholar may have two unique college students could have single name suppose they may be a scholar referred to as Rebekah and they are healing or there can be some other college students having recuperation however the roll numbers could be constantly be different so it'd be the primary key so what what's it the replica values could not be there and it should not take delivery of null fee that is for roll range there should be some fee the blank fee should now not be there so the four number one key the primary issue is it need to uniquely perceive the attribute k. it'd be uniquely identifying the attribute that is the first issue the second one factor is it must not accept null values and the 0.33 aspect is it need to not take delivery of reproduction values so you can do not forget this stuff about the primary key now the line is there most effective one candidate key can be a number one key.
2 : Unique Key
second is the precise key so there is a similarity between the number one key and the specific key see the four for the number one key. We learned 3 matters that it's far you no longer uniquely identify file so for the specific key additionally it is the identical it should uniquely identify the document OK. the next element is for example take the cope with okay so cope with for every student might be extraordinary so it would uniquely perceive the scholar in a unmarried lecture room okay but it's far like a number one key in this example that is it uniquely identifies a record however it is able to accept null values and it cannot have reproduction values so the issue is it need to uniquely identify a file so it can not have duplicate values it's miles just like the primary key handiest however it could accept null values so that is the primary factor the unique key the number one care unit key there's handiest one difference primary key. It cannot be given null fee and the particular key it could be given null cost so these are nearly similar however they're not same because precise key it can't have duplicate values. it is just like the primary key only however it is able to accept null values while the number one key it can not receive null values let's go to the subsequent key that is an alternate key exchange secret's a key which can paintings as a number one key so exchange key approach it's miles change to the number one key basically it's far a candidate key that isn't a number one key so right here additionally we have the time period candidate key we will undergo it what's a candidate key? so it's miles everything already it is able to paintings as a primary key which means the belongings of the alternate key is it should uniquely perceive okay it need to be unique the second should be no it can not have null values now not null the values cannot be null and it cannot have duplicate values ok so it's far the all the homes of the change key might be same to that of the number one key the following one is the candidate key so the candidate key is what it is also a fixed of 1 or more at buttes it may be single attributed alt can you multi or double click the primary factor it it simply unique it uniquely identifies a desk and it is able to be there may be a couple of candidate key in one desk and every candidate key a can paintings as a primary key so each candidate can key may be a primary key and each candidate key may be a exchange key so from the candidate key gets alternate keys and from the trade keys gets the number one keys so the houses of talented key would be is the identical this is it have to be specific it should be not null and it must be no longer replica it have to not have duplicate values OK so it's miles much like number one key.we will say every candidate key can be a primary key as an instance of in our preceding example we said roll number and registration quantity are both they may be each have particular values and each cannot have null values and each can not have duplicates so but one only one may be the number one key either we are able to take roll variety as a primary key or registration wide variety as a number one key while those each keys are there these each are the candidate keys out of these candidate key one key might be chosen because the number one key
3 : Super Key
terrific key set of 1 or more keys on or more than one keys that may be used to become aware of document so that you can say that the exquisite key is a fantastic set it's far the remarkable set of what it's miles a terrific set of primary key it's miles a tremendous set of candidate keys and it is the extremely good set of specific key and change key so till now whatever keys we have examine extremely good secret's the exceptional set of all keys.
4 : Composite Key
A key with one characteristic is a unmarried key k. Composite secret is a key which contains multiple attributes a couple of field or columns or a couple of attribute it's far a composite kid may be candidate right here primary key assume one isn't always a position function number on my own. suppose it cannot explicit role variety on my own is sufficient to be a but what a port if we combine call with date of what name on my own isn't always a number one key data but by myself is not a primary key however we combine call and date of start it may become a number one key so this is honestly what it's miles called it's miles a composite key that it consists of of two attributes call and date of birth so any key which has multiple characteristic had referred to as a organization composite key or it could additionally be known as as the compound key OK the following is the overseas key a foreign secret is a area within the database this is number one key to the any other desk think we've tables table 1 and desk 2 so the primary key of primary key of desk 1 with the intention to act as a foreign key of desk 2 as an instance table 1 as a student database and strong 2 is of teacher database OK in order that there might be some serial number for instructors or there could be a few worker wide variety for teachers okay so on this table think for pupil the this pupil is taught by way of the precise trainer X 1 so the employment quantity on this desk it might be a number one key a key of the teacher desk it would be used as a foreign key within the pupil table or the enrollment range of the student can be used as in foreign key in instructor desk so this is the overseas key so till now we had examine what number of keys you may go through they all first as a number one key 2d as the particular key 1/3 one was the trade key then it we had the candidate key then we had exquisite keys that we had composite keys and then at closing we had the overseas key so this was all i purchased the key's in database control device wish you appreciated.
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