mydb=> create table test_1 (id integer, name varchar(32));  
CREATE TABLE
mydb=> insert into test_1 values (1,'a'),(2,'b'),(3,'c');  
INSERT 0 3
mydb=> create table test_1_bak as select * from test_1 where 1=2;  
SELECT 0
mydb=> select * From test_1;  
id | name  
----+------  
 1 | a  
 2 | b  
 3 | c  
(3 rows)
mydb=> select * from test_1_bak;  
id | name  
----+------  
(0 rows)

mydb=> WITH deleted as (delete from test_1 where id=1 returning id,name)  
mydb-> insert into test_1_bak select * From deleted;  
INSERT 0 1

mydb=> select * from test_1;  
id | name  
----+------  
 2 | b  
 3 | c  
(2 rows)

mydb=> select * from test_1_bak;  
id | name  
----+------  
 1 | a  
(1 row)

mydb=> WITH test_1_deleted as (delete from test_1 where id=2 returning *)  
mydb-> select * from test_1_deleted;  
id | name  
----+------  
 2 | b  
(1 row)
mydb=> select * from test_1;  
id | name  
----+------  
 3 | c  
(1 row)

mydb=> insert into test_1 select generate_series(4,10),'c';  
INSERT 0 7

mydb=> select * from test_1;  
id | name  
----+------  
 3 | c  
 4 | c  
 5 | c  
 6 | c  
 7 | c  
 8 | c  
 9 | c  
10 | c  
(8 rows)

mydb=> create table test_2 (id integer , name varchar(32));  
CREATE TABLE

mydb=> insert into test_2 select generate_series(1,10000),'AAA';  
INSERT 0 10000

mydb=> select * From test_2 limit 3;  
id | name  
----+------  
 1 | AAA  
 2 | AAA  
 3 | AAA

mydb=> WITH test_1_deleted as (delete from test_1 where id<7 returning *) ,  
mydb-> delete_count as (select count(*) as total from test_1_deleted)  
mydb-> update test_2  
mydb-> set name='this is a test'  
mydb-> from delete_count d  
mydb-> where id=d.total;  
UPDATE 1

mydb=> select * From test_2 where name='this is a test';  
id | name  
----+----------------  
 4 | this is a test