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SELECT SUBSTR(A.COLUMN_NAME, 1, 15) COLUMN_NAME
     , DECODE(B.CONSTRAINT_TYPE
            , 'P', 'PRIMARY KEY'
            , 'U', 'UNIQUE KEY'
            , 'C', 'CHECK OR NOT NULL'
            , 'R', 'FOREIGN KEY') CONSTRAINT_TYPE
     , A.CONSTRAINT_NAME CONSTRAINT_NAME
  FROM USER_CONS_COLUMNS A
     , USER_CONSTRAINTS B
 WHERE A.TABLE_NAME = 'USERS'
   AND A.TABLE_NAME = B.TABLE_NAME
   AND A.CONSTRAINT_NAME = B.CONSTRAINT_NAME
 ORDER BY 1, 2;