Explain assignment, expressions and operator precedence in PL/SQL

Assignment is := (the SQL = is equality only). String concatenation is ||. Precedence, highest first: ** (exponentiation) and unary +/-, then * and /, then binary + - ||, then comparison operators, then NOT, then AND, then OR. NULL propagates through arithmetic (1 + NULL is NULL). When in doubt, parenthesise — especially mixed AND/OR conditions.

DECLARE
  v_a NUMBER := 2;
  v_b NUMBER := 3;
  v_c NUMBER := 4;
BEGIN
  DBMS_OUTPUT.PUT_LINE(v_a + v_b * v_c);        -- 14, not 20
  DBMS_OUTPUT.PUT_LINE((v_a + v_b) * v_c);      -- 20
  DBMS_OUTPUT.PUT_LINE(2 ** 3 ** 2);            -- 512 (right-associative)
END;
/