對於Oracle analyze table的使用總結 . 對於Oracle analyze table的使用總結 .
analyze table 一般可以指定分析： 表，所有字段，所有索引字段，所有索引。 若不指定則全部都分析。
SQL> analyze table my_table compute statistics;
SQL> analyze table my_table compute statistics for table for all indexes for all columns;
SQL> analyze table my_table compute statistics for table for all indexes for all indexed columns;
其中：
SQL> analyze table my_table compute statistics;
等價於：
SQL> analyze table my_table compute statistics for table for all indexes for all columns;
sample:
analyze table t1 compute statistics for table;
analyze table t2 compute statistics for all columns;
analyze table t3 compute statistics for all indexed columns;
analyze table t5 compute statistics for all indexes;
analyze table t4 compute statistics; (不指定）
另外，可以刪除分析數據：
SQL> analyze table my_table delete statistics;
SQL> analyze table my_table delete statistics for table for all indexes for all indexed columns;
http://wfly2004.blog.163.com/blog/static/1176427201042891042233/
首先創建四個臨時表t1,t2,t3,t4,和他們相對應的索引
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代碼:
create table t1 as select * from user_objects;
create table t2 as select * from user_objects;
create table t3 as select * from user_objects;
create table t4 as select * from user_objects;
create unique index pk_t1_idx on t1(object_id);
create unique index pk_t2_idx on t2(object_id);
create unique index pk_t3_idx on t3(object_id);
create unique index pk_t4_idx on t4(object_id);
查看這個時候各個表對應的數據庫統計信息(表,字段,索引)
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代碼:
--查看表的統計信息
select table_name,num_rows,blocks,empty_blocks from user_table where table_names in ('T1','T2','T3','T4');
TABLE_NAME NUM_ROWS BLOCKS EMPTY_BLOCKS
T1
T2
T3
T4
--查看字段的統計信息
select table_name,column_name,num_distinct,low_value,high_value,density from user_tab_columns where table_name in ('T1','T2','T3','T4');
TABLE_NAME COLUMN_NAME NUM_DISTINCT LOW_VALUE HIGH_VALUE DENSITY
T1 OBJECT_NAME
T1 SUBOBJECT_NAME
T1 OBJECT_ID
T1 DATA_OBJECT_ID
T1 OBJECT_TYPE
T1 CREATED
T1 LAST_DDL_TIME
T1 TIMESTAMP
T1 STATUS
T1 TEMPORARY
T1 GENERATED
T1 SECONDARY
T2 OBJECT_NAME
T2 SUBOBJECT_NAME
T2 OBJECT_ID
T2 DATA_OBJECT_ID
T2 OBJECT_TYPE
T2 CREATED
T2 LAST_DDL_TIME
T2 TIMESTAMP
T2 STATUS
T2 TEMPORARY
T2 GENERATED
T2 SECONDARY
T3 OBJECT_NAME
T3 SUBOBJECT_NAME
T3 OBJECT_ID
T3 DATA_OBJECT_ID
T3 OBJECT_TYPE
T3 CREATED
T3 LAST_DDL_TIME
T3 TIMESTAMP
T3 STATUS
T3 TEMPORARY
T3 GENERATED
T3 SECONDARY
T4 OBJECT_NAME
T4 SUBOBJECT_NAME
T4 OBJECT_ID
T4 DATA_OBJECT_ID
T4 OBJECT_TYPE
T4 CREATED
T4 LAST_DDL_TIME
T4 TIMESTAMP
T4 STATUS
T4 TEMPORARY
T4 GENERATED
T4 SECONDARY
--查看索引的統計信息
select table_name,index_name,blevel,leaf_blocks,distinct_keys,
avg_leaf_blocks_per_key avg_leaf_blocks,avg_data_blocks_per_key avg_data_blocks,clustering_factor,num_rows
from user_indexes where table_name in ('T1','T2','T3','T4');
TABLE_NAME INDEX_NAME BLEVEL LEAF_BLOCKS DISTINCT_KEYS AVG_LEAF_BLOCKS AVG_DATA_BLOCKS CLUSTERING_FACTOR NUM_ROWS
T1 PK_T1_IDX
T2 PK_T2_IDX
T3 PK_T3_IDX
T4 PK_T4_IDX
現在我們分別對這個表做不同形式的analyze table處理
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代碼:
analyze table t1 compute statistics for table;
analyze table t2 compute statistics for all columns;
analyze table t3 compute statistics for all indexed columns;
analyze table t4 compute statistics;
我們再回頭看看這是的oracle數據庫對於各種統計信息
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代碼:
--這是對於表的統計信息
select table_name,num_rows,blocks,empty_blocks from user_tables where table_name in ('T1','T2','T3','T4');
TABLE_NAME NUM_ROWS BLOCKS EMPTY_BLOCKS
T1 3930 55 1
T2
T3
T4 3933 55 1
--我們可以據此得出結論,只有我們在analyze table命令中指定了for table或者不指定任何參數的時候,oracle數據庫才會給我們統計基於表的統計信息
--這是對於表中字段的統計信息
select table_name,column_name,num_distinct,low_value,high_value,density from user_tab_columns where table_name in ('T1','T2','T3','T4');
TABLE_NAME COLUMN_NAME NUM_DISTINCT LOW_VALUE HIGH_VALUE DENSITY
T1 OBJECT_NAME
T1 SUBOBJECT_NAME
T1 OBJECT_ID
T1 DATA_OBJECT_ID
T1 OBJECT_TYPE
T1 CREATED
T1 LAST_DDL_TIME
T1 TIMESTAMP
T1 STATUS
T1 TEMPORARY
T1 GENERATED
T1 SECONDARY
T2 OBJECT_NAME 3823 41423030 D3F1BBB736D4C2B7DDCFFABBA7C7E5B5A5 .000270447891062615
T2 SUBOBJECT_NAME 77 503031 52455354 .012987012987013
T2 OBJECT_ID 3930 C304062D C30F4619 .000254452926208651
T2 DATA_OBJECT_ID 3662 C304062D C30F4619 .000273074822501365
T2 OBJECT_TYPE 15 4441544142415345204C494E4B 56494557 .000127194098193844
T2 CREATED 3684 7867081E111F33 7868071211152F .000547559423988464
T2 LAST_DDL_TIME 3574 7867081E11251B 7868071211152F .000565522924083892
T2 TIMESTAMP 3649 323030332D30382D33303A31363A33303A3530 323030342D30372D31383A31363A32303A3436 .000559822349362313
T2 STATUS 2 494E56414C4944 56414C4944 .000127194098193844
T2 TEMPORARY 2 4E 59 .000127194098193844
T2 GENERATED 2 4E 59 .000127194098193844
T2 SECONDARY 2 4E 59 .000127194098193844
T3 OBJECT_NAME
T3 SUBOBJECT_NAME
T3 OBJECT_ID 3931 C304062D C30F461A .000254388196387688
T3 DATA_OBJECT_ID
T3 OBJECT_TYPE
T3 CREATED
T3 LAST_DDL_TIME
T3 TIMESTAMP
T3 STATUS
T3 TEMPORARY
T3 GENERATED
T3 SECONDARY
T4 OBJECT_NAME 3825 41423030 D3F1BBB736D4C2B7DDCFFABBA7C7E5B5A5 .000261437908496732
T4 SUBOBJECT_NAME 77 503031 52455354 .012987012987013
T4 OBJECT_ID 3932 C304062D C30F461B .000254323499491353
T4 DATA_OBJECT_ID 3664 C304062D C30F461B .00027292576419214
T4 OBJECT_TYPE 15 4441544142415345204C494E4B 56494557 .0666666666666667
T4 CREATED 3685 7867081E111F33 78680712111530 .000271370420624152
T4 LAST_DDL_TIME 3575 7867081E11251B 78680712111530 .00027972027972028
T4 TIMESTAMP 3650 323030332D30382D33303A31363A33303A3530 323030342D30372D31383A31363A32303A3437 .000273972602739726
T4 STATUS 2 494E56414C4944 56414C4944 .5
T4 TEMPORARY 2 4E 59 .5
T4 GENERATED 2 4E 59 .5
T4 SECONDARY 2 4E 59 .5
/*
在這個結果中我們可以看到,oracle數據庫給t2,t4的所有字段都做了統計信息.
對表t3的object_id(索引字段)做了統計信息.
由此得出結論,
在指定for all columns 和不指定任何參數的時候oracle會給所有字段做統計信息,在指定for indexed columns時,oracle只給[b]有索引的字段進行字段信息統計[/b],如果我們別有必要給所有字段統計信息時,這個屬性就很有用了.
*/
--這里是對於索引的統計信息
select table_name,index_name,blevel,leaf_blocks,distinct_keys,
avg_leaf_blocks_per_key avg_leaf_blocks,avg_data_blocks_per_key avg_data_blocks,clustering_factor,num_rows
from user_indexes where table_name in ('T1','T2','T3','T4');
TABLE_NAME INDEX_NAME BLEVEL LEAF_BLOCKS DISTINCT_KEYS AVG_LEAF_BLOCKS AVG_DATA_BLOCKS CLUSTERING_FACTOR NUM_ROWS
T1 PK_T1_IDX
T2 PK_T2_IDX
T3 PK_T3_IDX
T4 PK_T4_IDX 1 9 3932 1 1 2143 3932
--從這里我們可以看出,只有表t4有索引統計信息.
--再綜合前面的我們就會發現,如果在運行analyze table是我們不指定參數,oracle將收集對於特定表的所有統計信息(表,索引,表字段的統計信息)
補充,truncate命令不修改以上統計信息
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代碼:
truncate table t1;
truncate table t2;
truncate table t3;
truncate table t4;
--我們在查看表和索引的統計信息
select table_name,num_rows,blocks,empty_blocks from user_tables where table_name in ('T1','T2','T3','T4');
TABLE_NAME NUM_ROWS BLOCKS EMPTY_BLOCKS
T1 3930 55 1
T2
T3
T4 3933 55 1
--索引的統計信息
select table_name,index_name,blevel,leaf_blocks,distinct_keys,
avg_leaf_blocks_per_key avg_leaf_blocks,avg_data_blocks_per_key avg_data_blocks,clustering_factor,num_rows
from user_indexes where table_name in ('T1','T2','T3','T4');
TABLE_NAME INDEX_NAME BLEVEL LEAF_BLOCKS DISTINCT_KEYS AVG_LEAF_BLOCKS AVG_DATA_BLOCKS CLUSTERING_FACTOR NUM_ROWS
T1 PK_T1_IDX
T2 PK_T2_IDX
T3 PK_T3_IDX
T4 PK_T4_IDX 1 9 3932 1 1 2143 3932
--我們再對以上各表做一次分析
analyze table t1 compute statistics for table;
analyze table t2 compute statistics for all columns;
analyze table t3 compute statistics for all indexed columns;
analyze table t4 compute statistics;
--現在再來查看表和索引的統計信息
select table_name,num_rows,blocks,empty_blocks,initial_extent,'8192' block_size from user_tables where table_name in ('T1','T2','T3','T4');
TABLE_NAME NUM_ROWS BLOCKS EMPTY_BLOCKS INITIAL_EXTENT BLOCK_SIZE
T1 0 0 8 65536 8192
T2 65536 8192
T3 65536 8192
T4 0 0 8 65536 8192
--索引的統計信息
select table_name,index_name,blevel,leaf_blocks,distinct_keys,
avg_leaf_blocks_per_key avg_leaf_blocks,avg_data_blocks_per_key avg_data_blocks,clustering_factor,num_rows
from user_indexes where table_name in ('T1','T2','T3','T4');
TABLE_NAME INDEX_NAME BLEVEL LEAF_BLOCKS DISTINCT_KEYS AVG_LEAF_BLOCKS AVG_DATA_BLOCKS CLUSTERING_FACTOR NUM_ROWS
T1 PK_T1_IDX
T2 PK_T2_IDX
T3 PK_T3_IDX
T4 PK_T4_IDX 0 0 0 0 0 0 0
--由此得出結論,truncate命令不會修改數據的統計信息,
--也就是如果我們想讓CBO利用合理利用數據的統計信息的時候,需要我們及時的使用analyze命令或者dbms_stats重新統計數據的統計信息