SQL Server Constraints in the table

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A SQL Server Database could have multiple tables and each table that has to be stored based on some rules. These rules are the possible checks & conditions which allows you to ensure the data validations before it is being inserted into a specific table.

SQL Server Constraints Types

SQL server constraints can be divided primarily into :

  1. SQL Server Table level constraints
  2. SQL Server Column level constraints
S. NoSQL Server Constraint Table / Column LevelDescription
1NOT NULL Column LevelColumn value cannot be specified as NULL
2UNIQUEColumn Levelall values in the column need to be UNIQUE
3CHECKColumn Level all values in a column satisfies a specific condition
4DEFAULTColumn Levelspecifies a DEFAULT value for the column
5INDEXTable Levelapply indexes make the data retrieval fast
6 PRIMARY KEYColumn LevelUnique identifier for the column. Combination of NOT NULL and UNIQUE values
7 FOREIGN KEYColumn LevelIdentifies the Column with Unique values in another table referenced in another table.

SQL Server Constraints can be applied :

  1. Create Table
  2. Alter Table

Syntax: SQL Server ADD Constraints in Table

CREATE TABLE table_name (
table_col1 datatype constraint,
table_col2 datatype constraint,
table_col3 datatype constraint,n
….

table_col3 datatype constraint
);

CREATE TABLE oracleappshelpStudents ( StudentId INT IDENTITY PRIMARY KEY, UserId INT REFERENCES oracleappshelpUsers (UserId), Email VARCHAR(256) , CreatedBy VARCHAR(128) NOT NULL, UpdatedBy VARCHAR(128) NOT NULL, CreatedDate DATETIME NOT NULL, UpdatedDate DATETIME NOT NULL )

We will be discussing in separate blog for each Constraint . Please refer the below given links

SQL Server Not Null Constraint in the table

SQL Server Primary Key / Foreign Key Constraint in the table

SQL Server Default Constraint Check

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