If you want to only update on rows that are not currently uppercase (instead of all rows), you'd need to identify the difference using COLLATE
like this:
UPDATE MyTable
SET MyColumn = UPPER(MyColumn)
WHERE MyColumn != UPPER(MyColumn) COLLATE Latin1_General_CS_AS
Cases sensitivity is based on your collation settings, and is typically case insensitive by default.
Collation can be set at the Server, Database, Column, or Query Level:
-- Server
SELECT SERVERPROPERTY('COLLATION')
-- Database
SELECT name, collation_name FROM sys.databases
-- Column
SELECT COLUMN_NAME, COLLATION_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE CHARACTER_SET_NAME IS NOT NULL
Collation Names specify how a string should be encoded and read, for example:
Latin1_General_CI_AS
? Case InsensitiveLatin1_General_CS_AS
? Case SensitiveSource: Stackoverflow.com