问题： 生产上曾经出现过因外键上没有索引导致死锁情况，经常需要查找没有索引的外键，以下给出从网上找到的SQL（忘记出处，见谅），整理于此备用。
column columns format a20 word_wrapped column table_name format a30 word_wrapped
select decode( b.table_name, NULL, ‘****‘, ‘ok‘ ) Status, a.table_name, a.columns, b.columns from ( select substr(a.table_name,1,30) table_name, substr(a.constraint_name,1,30) constraint_name, max(decode(position, 1, substr(column_name,1,30),NULL)) || max(decode(position, 2,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position, 3,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position, 4,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position, 5,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position, 6,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position, 7,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position, 8,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position, 9,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position,10,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position,11,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position,12,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position,13,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position,14,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position,15,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(position,16,‘, ‘||substr(column_name,1,30),NULL)) columns from user_cons_columns a, user_constraints b where a.constraint_name = b.constraint_name and b.constraint_type = ‘R‘ group by substr(a.table_name,1,30), substr(a.constraint_name,1,30) ) a, ( select substr(table_name,1,30) table_name, substr(index_name,1,30) index_name, max(decode(column_position, 1, substr(column_name,1,30),NULL)) || max(decode(column_position, 2,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position, 3,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position, 4,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position, 5,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position, 6,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position, 7,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position, 8,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position, 9,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position,10,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position,11,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position,12,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position,13,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position,14,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position,15,‘, ‘||substr(column_name,1,30),NULL)) || max(decode(column_position,16,‘, ‘||substr(column_name,1,30),NULL)) columns from user_ind_columns group by substr(table_name,1,30), substr(index_name,1,30) ) b where a.table_name = b.table_name (+) and b.columns (+) like a.columns || ‘%‘ /