IF NOT EXISTS

I can't find a way to convert an IF exists from microsoft sql to hana.

With mssql, IF can be used to execute a sql command only if the condition is true.

Someone have an idea on how to do this ?

code:

if not exists(  select * from SYS.TABLE_COLUMNS where Schema_Name = CURRENT_SCHEMA AND TABLE_NAME = 'TableName' AND COLUMN_NAME = 'Column'      )

alter table TableName

...