Oracle 查詢表與表之間的 主外來鍵關係

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查詢表之間的主外來鍵關係
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Select b.table_name 主鍵表名,
           b.column_name 主鍵列名,
           a.table_name 外來鍵表名,
           a.column_name 外來鍵列名
From (Select a.constraint_name,
                       b.table_name,
                       b.column_name,
                       a.r_constraint_name
          From user_constraints a, user_cons_columns b
         Where a.constraint_type = 'R'
           And a.constraint_name = b.constraint_name) a,
       (Select Distinct a.r_constraint_name, b.table_name, b.column_name
          From user_constraints a, user_cons_columns b
         Where a.constraint_type = 'R'
           And a.r_constraint_name = b.constraint_name) b
Where a.r_constraint_name = b.r_constraint_name