update query help

sql 2000

i have three tables

1- create table mytab(id_no varchar(5), Counter smallint))
2- create table Rectab(id_no varchar(5), refno smallint))
3- create table Lib_tab(refno smallint)

insert into mytab values(1,null)
insert into mytab values(2,null)
insert into mytab values(3,null)
insert into mytab values(4,null)

-- Rectab has duplicate values

insert into Rectab values(1,1)
insert into Rectab values(1,1)
insert into Rectab values(1,2)
insert into Rectab values(1,2)
insert into Rectab values(1,2)
insert into Rectab values(1,3)
insert into Rectab values(2,1)
insert into Rectab values(2,1)
insert into Rectab values(3,2)
insert into Rectab values(3,2)
insert into Rectab values(3,2)
insert into Rectab values(3,3)
insert into Rectab values(4,3)
insert into Rectab values(4,3)
insert into Rectab values(4,2)
insert into Rectab values(4,1)
insert into Rectab values(4,1)

---Libtab Library table

insert into Lib_tab values(1)
insert into Lib_tab values(2)
insert into Lib_tab values(3)
insert into Lib_tab values(4)
insert into Lib_tab values(5)


i want to update mytab in manner that i want to get distinct count
(distinct id_no,refno) of rectab in counter column of my tab, vALUES of
refno MUST EXIST IN Lib_tab e.g out put should like

select * from mytab

id_no counter
1 3
2 1
3 2
4 3

what will be the update query



regards

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