postgres copy value from one column to another code example

Example 1: copy value from one column to another postgres

UPDATE table SET columnB = columnA;

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;