if object_id('TMain') is not null drop table TMain
if object_id('TExt') is not null drop table TExt
go
Create table TMain 
( Id   int Null, 
  Col1 varchar(100) Null, 
  Col2 varchar(100) Null, 
  Col3 varchar(100)Null
)
go
Create table TExt
(
  TMain_Id  int,
  param_KEY varchar(100),
  value     varchar(100)
)
go
insert into TMain(Id)
Select 1 union Select 2 union select 3
go 
insert into TExt(TMain_Id, param_KEY, value)
Select 1, 'Col1', 'Value1_1' union Select 1, 'Col2', 'Value1_2' union Select 1, 'Col3', 'Value1_3' union
Select 2, 'Col1', 'Value2_1' union Select 2, 'Col2', 'Value2_2' union Select 2, 'Col3', 'Value2_3'
go 

update TMain
  Set Col1 = (select value from TExt where TExt.TMain_Id = TMain.Id and TExt.param_KEY = 'Col1'),
      Col2 = (select value from TExt where TExt.TMain_Id = TMain.Id and TExt.param_KEY = 'Col2'),
      Col3 = (select value from TExt where TExt.TMain_Id = TMain.Id and TExt.param_KEY = 'Col3')

update TMain
  Set Col1 = Case when param_KEY = 'Col1' then value End,
      Col2 = Case when param_KEY = 'Col2' then value End,
      Col3 = Case when param_KEY = 'Col3' then value End
from TExt, TMain
  where TExt.TMain_Id = TMain.Id