[SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] [Y] underscore (_), pattern-matching character  UNION ALL set operator  2nd      comparing tables  UNION clause, data sets, creating custom  union compatibility conditions  UNION operation compared to UNION ALL  UNION queries      ANSI join syntax and      full outer joins  UNION set operator  2nd  UPDATE statement      CASE expression      collections and      DECODE function      DML (Data Manipulation Language)      inline views      join views      multiple-column subqueries      optional updates      selective aggregation      WHERE clause and  USER_UPDATABLE_COLUMNS data dictionary view  USING clause  UTC (Coordinated Universal Time)