SQL update fields of one table from fields of another one

Question

I have two tables:

A [ID, column1, column2, column3]
B [ID, column1, column2, column3, column4]

A will always be subset of

Answer 1

You can use the non-standard FROM clause.

UPDATE b
SET column1 = a.column1,
  column2 = a.column2,
  column3 = a.column3
FROM a
WHERE a.id = b.id
AND b.id = 1