SQL CONSTRAINTS

Constraints are used to specify rules for data that can go into a table.

Constraints can be both column level and table level, which ensures the accuracy and authenticity of the data in the database.

The following constraints are commonly used in SQL:

  • NOT NULL - Checks that a column cannot have a NULL value

  • UNIQUE - Checks that all values in a column are unique or different from one another

  • PRIMARY KEY - A combination of a NOT NULL and UNIQUE. Uniquely identifies each row in a table. We can define only one Primary key in the table.

  • FOREIGN KEY - Uniquely identifies a row/record in another table.

  • CHECK - Checks that all values in a column satisfies a specific condition

  • DEFAULT - Sets a default value for a column when no value is specified.

INDEX – We can create Index on any table and retrieve data from the database very quickly.

Want More SQL Deep Dives

  1. SQL Introduction

  2. Database Overview

  3. Creating a Database

  4. Dropping a Database

  5. Table Fundamentals

  6. Table Types

  7. Datatypes in SQL

  8. DDL, DML, TCL & DCL

  9. Null & Not Null Values

  10. Creating Tables

  11. SQL - Constraints

  12. SQL - Index 

  13. SQL Inserting Data

  14. SQL Identity Columns

  15. Selecting Data

  16. Using Distinct

  17. SQL in NOT IN

  18. Using Top Clause

  19. Where Clause

  20. Group By

  21. Order By

  22. Having

  23. Exists

  24. Offset

  25. SQL - Operators

  26. Between

  27. Update

  28. Delete

  29. SQL - Aggregate Functions

  30. SQL - Introductions to Joins

  31. Table Alias

  32. SQL - Inner Join

  33. SQL - Left Join

  34. SQL - Right Join

  35. Full Join

  36. Self Join

  37. SQL Union

  38. Pivot

  39. Alter Command

  40. Limit Clause

  41. Truncate

  42. Drop

  43. Table Backup

  44. SQL - Normalization

  45. Subquery

  46. SQL - Views & Materialized Views

  47. Case Statement

  48. SQL Transactions

  49. SQL - Scaler Functions

  50. Working with Dates

  51. Grant revoke

  52. SQL - Performance Tunning

  53. Stored Procedure Basics

  54. Stuff function

  55. Keyword

  56. SQL - Miscellaneous