How To Use Alter Command In SQL SERVER

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Adding a Primary Key Constraint on Column

  ALTER TABLE employee ADD CONSTRAINT emp_id_pk PRIMARY KEY(emp_id)

Increasing the width of a column

  ALTER TABLE employee ALTER COLUMN emp_name varchar(100)

Decreasing the width of a column

  ALTER TABLE employee ALTER COLUMN emp_name varchar(50)

Changing the Data Type of Column

  ALTER TABLE employee ALTER COLUMN emp_name nvarchar(50)

Add a NULL Constraint on Column

  ALTER TABLE employee ALTER COLUMN emp_name nvarchar(50) NULL

Add a NOT NULL Constraint on Column

  ALTER TABLE employee ALTER COLUMN emp_name nvarchar(50) NOT NULL

Add a new Column on Table without any Constraint

  ALTER TABLE employee ADD emp_age varchar(10)

Add a new Column on Table with a Constraint

  ALTER TABLE employee ADD emp_code varchar(100) CONSTRAINT emp_code_uq UNIQUE

Drop a Column from Table

  ALTER TABLE employee DROP COLUMN emp_code

Adding a Check Constraint Column

  ALTER TABLE employee ADD CONSTRAINT emp_age_ck (emp_age > 18)


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