Question

I want to add or update columns using alter table if i am adding a new column i want show error. I am using the code below

 alter table Personal_Details alter columns DOB datetime 

if i uncheck the NULL to not NULL then it will shows column does not allow nulls; update fails;

i want to insert the fields in between columns not at end.

Plese fix my bug,

Thanks in advance.

Answer 1

The position of the column in the table declaration has nothing to do with its being NULL or NOT NULL.

If you are adding a column (of any type) which you want to be NOT NULL, i.e. you want to prohibit NULL values in that column, and the table already contains some rows, you must also provide some default value. For example:

ALTER TABLE Personal_Details
ADD COLUMN DOB datetime NOT NULL DEFAULT (GETDATE())

Otherwise the engine will attempt to add that column with NULLs as its values, which will violate the NOT NULL property, and the change, therefore, will be reverted.

Basically, the same applies when you want to set an existing column’s NOT NULL property on while the column already contains NULLs. But in this case you must explicitly eliminate the NULLs before the change by either replacing them with values or removing the respective rows.

Source:

• ALTER TABLE (Transact-SQL). (The particular section related to your problem is just above this code snippet.)