How to locate unindexed foreign keys

Two issues can be avoided if you index your foreign key columns:

  • Slow joins (Full Table Scans) between parent/child tables
  • Deadlocks when updating or deleting a parent key.

The following script is very helpfull in locating unindexed foreign keys:

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 || '%'
/

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