Oracle analyze table

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最新推荐文章于 2024-06-27 17:57:31 发布

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分类专栏： --------1.1 ORACLE 文章标签： oracle

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本文详细介绍了 Oracle 数据库中 Analyze Table 命令的不同用法及其对表、索引及字段统计信息的影响。通过具体示例展示了如何根据不同需求选择合适的参数来优化基于成本的优化器 (CBO) 的执行计划。

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oracle的联机文档描述了analyze的作用：
Use the ANALYZE statement to collect non-optimizer statistics, for example, to:

Collect or delete statistics about an index or index partition, table or table partition, index-organized table, cluster, or scalar object attribute.
Validate the structure of an index or index partition, table or table partition, index-organized table, cluster, or object reference (REF).
Identify migrated and chained rows of a table or cluster.

dbms_stats的作用主要是替代analyze的收集统计信息这一块的功能，且在这一方面做了相当大程度上的增强。

以你的analyze table abc compute statistics;
这条为例，生成的统计信息会存在于user_tables这个视图，查看一下select * from user_tables where table_name=’ABC’;
观察一下NUM_ROWS,BLOCKS,AVG_SPACE,AVG_ROW_LEN几列你就会明白，这就是变化。

收集统计信息的目的是为了使基于CBO的执行计划更加准确。

对于Oracle analyze table的使用总结 . 对于Oracle analyze table的使用总结 .
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。 若不指定则全部都分析。
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;  
等价于：
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，可以删除分析数据：
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/
首先创建四个临时表t1,t2,t3,t4,和他们相对应的索引 
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代码:
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);
查看这个时候各个表对应的数据库统计信息(表,字段,索引) 
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代码:
--查看表的统计信息
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                       
--查看字段的统计信息
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                               
--查看索引的统计信息
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          
现在我们分别对这个表做不同形式的analyze table处理 
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代码:
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;
我们再回头看看这是的oracle数据库对于各种统计信息 
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代码:
--这是对于表的统计信息
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
--我们可以据此得出结论,只有我们在analyze table命令中指定了for table或者不指定任何参数的时候,oracle数据库才会给我们统计基于表的统计信息
--这是对于表中字段的统计信息
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
/*
在这个结果中我们可以看到,oracle数据库给t2,t4的所有字段都做了统计信息.
对表t3的object_id(索引字段)做了统计信息.
由此得出结论,
在指定for all columns 和不指定任何参数的时候oracle会给所有字段做统计信息,在指定for indexed columns时,oracle只给[b]有索引的字段进行字段信息统计[/b],如果我们别有必要给所有字段统计信息时,这个属性就很有用了.
*/
--这里是对于索引的统计信息
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
--从这里我们可以看出,只有表t4有索引统计信息.
--再综合前面的我们就会发现,如果在运行analyze table是我们不指定参数,oracle将收集对于特定表的所有统计信息(表,索引,表字段的统计信息)
补充,truncate命令不修改以上统计信息
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代码:
truncate table t1;
truncate table t2;
truncate table t3;
truncate table t4;
--我们在查看表和索引的统计信息
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
--索引的统计信息
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
--我们再对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;
--现在再来查看表和索引的统计信息
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
--索引的统计信息
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
--由此得出结论,truncate命令不会修改数据的统计信息,
--也就是如果我们想让CBO利用合理利用数据的统计信息的时候,需要我们及时的使用analyze命令或者dbms_stats重新统计数据的统计信息
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