How to change column name and data type of a column cannot be done in one statement but first we need to change the column name and then data type, In this post we will check many other things like how to change data type of a column, how to drop a column, how to add a new column, how to make a column not nullable etc.
So first we will see how to change a column name as well as data type of the column, as I said we cannot do it in one statement but we first need to change the column name and then data type so let's see this:
Suppose we want to change the column
"BlogTypeID" to "Tags" from data type int to varchar(200) in Blogs table then
-- change column name BlogTypeID to Tags EXEC sp_rename 'blogs.BlogTypeID', 'Tags', 'COLUMN'
Once we will run this query we will get a warning "Caution: Changing any part of an object name could break scripts and stored procedures. It indicates that our existing procedures may break but our column name is changes, check the table.
Now we will alter the column data type
ALTER TABLE Blogs ALTER COLUMN Tags VARCHAR(200)
Now our task is completed to change column and column data type.
How to add a new column in a table
ALTER TABLE table_name ADD column_name datatype
To change the datatype to support 100 characters and make NOT NULL
ALTER TABLE table_name ALTER COLUMN column_name VARCHAR(100) NOT NULL
To change datatype and allow NULLs for column
ALTER TABLE table_name ALTER COLUMN column_name DATETIME NULL
To drop a column from a table
ALTER TABLE table_name DROP COLUMN column_name
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