外來鍵列沒有索引，容易導致enq: tm - contention等待事件，所以外來鍵列必須建立索引。
（1）下面的sql語句可以定位出哪些外來鍵約束沒有建立索引。
select table_name, constraint_name,
cname1
|| nvl2 (cname2, ',' || cname2, null)
|| nvl2 (cname3, ',' || cname3, null)
|| nvl2 (cname4, ',' || cname4, null)
|| nvl2 (cname5, ',' || cname5, null)
|| nvl2 (cname6, ',' || cname6, null)
|| nvl2 (cname7, ',' || cname7, null)
|| nvl2 (cname8, ',' || cname8, null) columns
from (select b.table_name, b.constraint_name,
max (decode (position, 1, column_name, null)) cname1,
max (decode (position, 2, column_name, null)) cname2,
max (decode (position, 3, column_name, null)) cname3,
max (decode (position, 4, column_name, null)) cname4,
max (decode (position, 5, column_name, null)) cname5,
max (decode (position, 6, column_name, null)) cname6,
max (decode (position, 7, column_name, null)) cname7,
max (decode (position, 8, column_name, null)) cname8,
count (*) col_cnt
from (select substr (table_name, 1, 30) table_name,
substr (constraint_name, 1, 30) constraint_name,
substr (column_name, 1, 30) column_name, position
from user_cons_columns) a,
user_constraints b
where a.constraint_name = b.constraint_name
and b.constraint_type = 'r'
group by b.table_name, b.constraint_name) cons
where col_cnt >
all (select count (*)
from user_ind_columns i
where i.table_name = cons.table_name
and i.column_name in
(cname1,
cname2,
cname3,
cname4,
cname5,
cname6,
cname7,
cname8
) and i.column_position <= cons.col_cnt
group by i.index_name)
/ （2）批量給沒有索引的外來鍵列建立索引
select 'create index ind_fk_'||table_name||' on '||table_name||' ('||columns||') online nologging;' from (
select table_name, constraint_name,
cname1
|| nvl2 (cname2, ',' || cname2, null)
|| nvl2 (cname3, ',' || cname3, null)
|| nvl2 (cname4, ',' || cname4, null)
|| nvl2 (cname5, ',' || cname5, null)
|| nvl2 (cname6, ',' || cname6, null)
|| nvl2 (cname7, ',' || cname7, null)
|| nvl2 (cname8, ',' || cname8, null) columns
from (select b.table_name, b.constraint_name,
max (decode (position, 1, column_name, null)) cname1,
max (decode (position, 2, column_name, null)) cname2,
max (decode (position, 3, column_name, null)) cname3,
max (decode (position, 4, column_name, null)) cname4,
max (decode (position, 5, column_name, null)) cname5,
max (decode (position, 6, column_name, null)) cname6,
max (decode (position, 7, column_name, null)) cname7,
max (decode (position, 8, column_name, null)) cname8,
count (*) col_cnt
from (select substr (table_name, 1, 30) table_name,
substr (constraint_name, 1, 30) constraint_name,
substr (column_name, 1, 30) column_name, position
from user_cons_columns) a,
user_constraints b
where a.constraint_name = b.constraint_name
and b.constraint_type = 'r'
group by b.table_name, b.constraint_name) cons
where col_cnt >
all (select count (*)
from user_ind_columns i
where i.table_name = cons.table_name
and i.column_name in
(cname1,
cname2,
cname3,
cname4,
cname5,
cname6,
cname7,
cname8
) and i.column_position <= cons.col_cnt
group by i.index_name)
)
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