Steps to modify a column in a temporal table in Sql Server

AlterTemporalTableColumn.sql

/*
Steps to alter a column in a Temporal Table 
e.g. Table "Employee" versioned by "EmployeeHistory", change column "LastName" from Null to Not Null
*/

ALTER TABLE [dbo].[Employee] SET (SYSTEM_VERSIONING = OFF);

-- fix any null entries in the primary and history tables:
UPDATE dbo.Employee        SET [LastName] = '' WHERE [LastName] IS NULL;
EXEC('UPDATE dbo.EmployeeHistory SET [LastName] = '''' WHERE [LastName] IS NULL');

ALTER TABLE [dbo].[Employee]
SET
(
SYSTEM_VERSIONING = ON (HISTORY_TABLE = [dbo].[EmployeeHistory])
);

ALTER TABLE dbo.Employee ALTER COLUMN [LastName] nvarchar(255) NOT NULL;