How to update data for another table in one UPDATE statement with data from one table

(1) How to update the data of another table in one UPDATE statement with the data of one table
Update AA
Set aa.ac=
(select top 1 dd from CC where CC.AA=AA.AA)
This statement updates each row in the AA table, and the specific execution process is
Iterate through each row of the AA table and then conditionally: Select top 1 dd from CC where CC.AA=AA.AA
Assign the column dd of the corresponding row in the CC table to the column AC of the AA table
(Note: Every column in the cc.aa= (<>) AA.AA,AA table will be updated)
(2) Update AA
Set aa.ac=
(select top 1 dd from CC where CC.AA=AA.AA)
where
Exists (SELECT * from CC where CC.AA=AA.AA)
This statement updates the satisfies condition in the AA table: Exists (SELECT * from CC where CC.AA=AA.AA)
All rows
Update AA
Set aa.ac=
(select top 1 dd from CC where CC.AA=AA.AA)
where
Aa.aa in (select AA from CC where AA.AA=CC.AA)
The statement is equivalent to the above statement (2)
(3) Update (select Aa.ac ac,cc.dd dd from AA,CC where AA.AA=CC.AA)
Set AC=DD
This statement also implements the same functionality, but it seems that SQL Server 2005 does not support this format, but it can be done in Oracle (this statement is simpler)