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SQL constraints

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SQL constraints are rules that a table's data must follow. The type of data that can be entered into a table is limited by constraints. This ensures that the data in the table is accurate and reliable. The action is cancelled if there is a conflict between the constraint and the data action.

When no value is supplied for a column, the DEFAULT Constraint provides a default value. UNIQUE Constraint ensures that every value in a column is unique. Each row/record in a database table is uniquely identified by the PRIMARY Key. FOREIGN KEY identifies a row/record in any database table in a unique way.

A constraint is defined as something that imposes a limit or restriction on something or prohibits something from happening. The fact that there are only so many hours in a day to complete something is an example of a restriction. A check is a device that restricts, limits, or regulates something.

Constraints are required for developing respect for other people's opinions and beliefs. It is required for the development of a society. Absence of restraint would result in the imposition of stronger groups' views and ideas, eventually leading to war. Controlling violence and resolving conflicts necessitates the use of constraints.

Constraints are used to ensure data integrity when updating, deleting, or inserting data into a table. If any operation in the database does not follow the rules stated by the constraint after it is placed, the operation is aborted.

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  2. Understanding SDLC Process
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  3. How to use LearnVern
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  4. Client Server Architecture
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  5. How to set up PHP Environment?
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  1. What is Data
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  2. What is Database
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  3. What is DBMS
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  4. SQL Queries and its types
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  5. Data Types in SQL - from 16
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  6. SQL constraints
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  7. Create, Drop & Show Database
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  8. SQL Create Table
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  9. SQL Insert & Select Statement
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  10. Operators in SQL
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  11. In & NOt in Condition
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  12. Null & Not Null Condition
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  13. Clauses in SQL
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  14. Understanding Having, Distinct & Group by
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  15. Update & Delete in SQL
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  16. Alter table command in SQL
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  17. MySQL Rename truncate Drop
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  18. Understanding Foreign key
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  19. MySQL joins
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  20. MySQL views
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  21. MySQL Function
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  22. MySQL Procedure
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  23. MySQL Trigger
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  24. Normalization
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  25. Assignment : MYSQL
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  1. Understanding PHP Program structure Comments in PHP
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  1. Variables in PHP
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  1. Arithmetic & Assignment Operators in PHP
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  2. Comparison & Logical Operators in PHP
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  3. Ternary Operator in PHP
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  3. Assignment : Array
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  1. Loops in PHP
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  2. More examples on Loops in PHP
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  2. Assignment : Header Functions
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  2. Assignment : Date Time Functions
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  1. Error Handling in PHP
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  1. File Upload in PHP
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  1. Database Connection in PHP Part 1
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  2. Database Connection in PHP Part 2
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  1. Crud - Registration and DB connection Part 1
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  2. Crud - Registration and DB connection Part 2
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  4. Read Operation
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  5. Update Operation Part 1
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  6. Update Operation Part 2
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  2. MySQL Interview Question 2
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  3. MySQL Interview Question 3
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