how to copy a column from another table postgres code example

Example 1: copy column from one table to another without column duplicate postgres

//Postgres Database Query
insert into table1(column1,column2)
select c1,c2
  from table2 a
 where not exists ( select 0 from table1 b where b.id = a.id )

Example 2: copy from one table to another postgres using matching column

UPDATE Table2 --format schema.table_name
SET 
ref_id2 = table1.ref_id1
FROM table1 -- mention schema name
WHERE table1.id = table2.id
AND 
table1.a_ref1 = table2.b_ref1;