How to update data types in SQL from a returned list

Question

I made a database and realized made a mistake where whole bunch of tables have nvarchar(255) data types in them. They were supposed to be datetime. I am trying to modify all of them by running a simple code.

First I ran the below code to identify all the tables and the relevant column names which have the word "date" in them as I know these are the columns who's data types needs to be changed:

select * 
from MyDatabase.INFORMATION_SCHEMA.COLUMNS c 
where c.COLUMN_NAME like '%date%'

I looked at the list and confirmed none of the columns have any data in them. Only some of them have NULL in them. Which I can delete those data if needed. Also only 3 in the returned list are not Null able; the rest are Null able. I can modify the not Nullable ones manually if its going to matter.

I was thinking like running a code like:

select * 
from MyDatabase.INFORMATION_SCHEMA.COLUMNS c 
where c.COLUMN_NAME like '%date%' and c.IS_NULLABLE = 'yes'

ALTER COLUMN c.COLUMN_NAME LIKE '%date%' DATETIME [NULL] -- for the Nullable items

With above code I was trying to use the logic from the below link: How do you change the datatype of a column in SQL Server?

Nevertheless, I know my above implementation is incorrect. Could anyone help me with the proper way? Thanks in advance

Answer 1

In mysql you could this. You can achieve the same results in other sql database services, just the syntax may be different.

select CONCAT('ALTER TABLE ', c.TABLE_NAME, ' MODIFY COLUMN ', c.COLUMN_NAME, ' 
DATETIME;') 
from INFORMATION_SCHEMA.COLUMNS c 
where c.COLUMN_NAME like '%date%' and c.TABLE_SCHEMA='database_name'

Basically you're retrieving all the columns with the word date and then using the CONCAT function to build alter queries. Then you just need to run the resulting queries.