Sometime because of identity column you dont have permission to insert values because identity column increment default

example:-

id	name	product	brand
1	swapnil	britaniya	good
2	bhavesh	mary	average

In this table id is identity column is u try to insert value on open table on id column it will not happen because column is readonly format when u insert new row it will automatically insert id 3

so if u want to insert third record id is 20 for that u have to do below code

SET IDENTITY_INSERT test ON

Insert Into test (Id,name,product,brand) VALUES (20,'wer','Product1','Brand1')

SET IDENTITY_INSERT test OFF

by using this code u can insert next id row to 20 successfully

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how to create identity column

select table right click design

column properties window display

select identityspecification =yes

isidentity =yes

identity increment =1

identity seed =1