4 Varieties of Integrity Constraints in SQL: The whole thing You Wish to Know [Updated]

SQL Number one key

A number one secret is a box in a database desk that uniquely identifies each and every row/report. This could also be one form of Integrity Constraint. Number one keys should have distinct values. Null values don’t seem to be allowed in a number one key column. A desk can simplest have one number one key, which may also be made up of a number of fields. It creates a composite key when a number of fields are used as a number one key

Syntax

Create desk table_name

(  

Column_name1 datatype NOT NULL,  

Column_name2 datatype,

…..

Column_namendatatype,

 PRIMARY KEY (column_name1)  

)  

Code 

create desk scholar(identification int now not null,identify varchar(20),marks int,grade varchar(5),number one key(identification));

make a choice * from scholar;

The picture depicted beneath demonstrates the desk created with identification, identify, marks, and grade fields.

Enter

Output

Rationalization

Via the use of the above question, it’ll create the desk named scholar with suitable fields. Identity belongs to the not-null constraints, the identify belongs to varchar datatype, marks belong to varchar datatype, and in the end, the identification box is ready to number one key constraints.

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Overseas key

Overseas keys assist be certain the consistency of your information whilst offering some ease. This could also be a kind of integrity constraint. You might be liable for keeping an eye on inter-table dependencies and holding their consistency from inside of your packages if you do not use global keys. In positive eventualities, doing so is not even that tricky. It’s just a topic of including a couple of extra delete sentences to make sure that all is so as.

Syntax

CREATE TABLE table_name1

(

 Column_name1 datatype NOT NULL,

 Column_name2 datatype ,

 …

Column_nameNdatatype ,

  PRIMARY KEY (Column_name1)

)

CREATE TABLE table_name2

(

  Column_name1 datatype NOT NULL,

  Column_name2 datatype  NOT NULL,

  Column_name3 datatype  ,

  ….

Column_nameNdatatype ,

  PRIMARY KEY (Column_name1, Column_name2),

  FOREIGN KEY (Column_name1) REFERENCES table_name2 (Column_name1) ON DELETE CASCADE

)

Code

CREATE TABLE studnew

(

stu_id   INT NOT NULL,

stu_name varchar(20),

stu_class Varchar(20),

  PRIMARY KEY (stu_id)

)

CREATE TABLE classnew

(

stu_id   INT NOT NULL,

class_id INT NOT NULL,

  PRIMARY KEY (stu_id, class_id),

  FOREIGN KEY (stu_id) REFERENCES stud (stu_id) ON DELETE CASCADE

)

Make a choice * from studnew

Enter

Output

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NOT NULL CONSTRAINTS

The now not null constraint tells a column that it cannot have any null values in it. This could also be a kind of integrity constraint. This forces a box to all the time have a price, which means you’ll be able to’t create a brand new report or alternate an present one with out including a price to it.

Syntax

Create desk table_name

(  

Column_name1 datatype NOT NULL,  

Column_name2 datatype,

……

Column_namendatatype,

)  

Code

create desk student1(identification int now not null,identify varchar(20),marks int,grade varchar(5));

make a choice * from student1;

Enter

Output

Distinctive Key

A choice of a number of desk fields/columns that uniquely determine a report in a database desk is referred to as a novel key. This could also be a kind of integrity constraint. It’s very similar to a number one key, however it will possibly simplest settle for one null worth and can not have reproduction values. Each the particular key and the main key make sure that a column or staff of columns is exclusive. A Distinctive secret is generated routinely.

Syntax

CREATE TABLE Table_name (

    Column_Name1 DataType NOT NULL UNIQUE,

    Column_Name2 DataType NOT NULL,

    Column_Name3 DataType,

         …….

Column_NameNDataType

);

Code

CREATE TABLE Student_DB (

S_ID int NOT NULL UNIQUE,

L_Name varchar(255) NOT NULL,

F_Name varchar(255),

Age int);

Enter

Output

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Number one Key Vs. Distinctive Key

In the case of number one keys and distinctive keys, it is very important to observe a couple of laws to create a database. The next tips be certain consistency within the database fashion.

• It will have to specify the Number one Key for each and every desk within the database. This is not going to simplest spice up database potency total however may also make sure that information is related and constant.
• Come with an identification column in each and every desk. You can use it as a number one key column, with an unsigned integer shape and identification set to true (1,1). As you upload rows, the RDBMS will routinely generate number one key values. The usage of integers as Number one Keys additionally will increase potency.
•  With the exception of Number one Keys, which include distinctive values, it will have to specify all attributes as UNIQUE. You might outline this assets for a unmarried characteristic or a bunch of attributes.

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Shedding Constraints

The ALTER TABLE command is used to take away constraints.

Except the prohibit drop possibility is indexed, when a number one/distinctive secret is dropped, global keys referencing the important thing being dropped also are dropped. When the comparable tables/schemas/databases are got rid of, constraints also are got rid of. The cascade/prohibit drop choices are supported through the drop instructions.

DROP a UNIQUE Constraint

The next syntax and examples assist to drop distinctive constraint from the desk:

Syntax

ALTER TABLE TABLE_NAME DROP CONSTRAINT UNIQUE _KEY FIELD

Code

ALTER TABLE Student_DB

 DROP CONSTRAINT  UKlname;

Enter

Output

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Shedding Number one Key Constraints

You’ll reach maximum shedding constraints through the use of adjust command. To take out the main key declared within the desk, employ the next code. This will likely take out the main key assigned to a specific box.

Code

ALTER TABLE retail outlets

drop pkkey;

Enter

Output

Shedding Overseas key Constraint

Code

ALTER TABLE Orders

DROP FOREIGN KEY FK_pid;

 ALTER TABLE Orders

DROP CONSTRAINT FK_pid;

Enter

Output

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Conclusion

SQL integrity constraint specifies a demand that each and every row in a database desk should fulfill. A predicate constraint is wanted. It will confer with a unmarried desk column or a couple of desk columns. Relying at the lifestyles of NULLs, the predicate’s end result is also TRUE, FALSE, or UNKNOWN. The limitations evaluation to UNKNOWN if the predicate evaluates to UNKNOWN.

Number one Key Constraints, Overseas Key Constraints, Distinctive Key Constraints, NOT NULL Constraints, Comparability between Number one Key and Distinctive Key Constraints, and Shedding the Constraints with syntax, instance, and screenshots are given through executing the codes on this article.

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