从一个表中获取值并使用该值查询另一个表

TableA
---------------
ParamA ¦ ParamB
---------------
  695  ¦  Test

TableB
---------------
ParamA ¦ ParamC
---------------
  695  ¦ Test2

TableB WHERE ParamA = ParamA FROM TableA

SELECT ParamA FROM TableA WHERE ParamB = @ParamB

UPDATE ParamC = 'NULL'

UPDATE ClassDetails
SET ValidTo = 'NULL'
WHERE Class = Classes.ClassId AND Classes.ClassName = @ClassName;

UPDATE b
SET    ParamC = NULL
FROM   TableB b
       INNER JOIN TableA a ON a.ParamA = b.ParamA
WHERE  a.ParamB = @ParamB