ClickHouse是俄罗斯的Yandex于2016年开源的列式存储数据库(DBMS),使用C++语言编写,主要用于在线分析处理查询(OLAP),能够使用SQL查询实时生成分析数据报告。 OLAP(On-Line Analytical Processing)翻译为联机分析处理,专注于分析处理,从对数据库操作来看,OLAP是对数据的查询; OLTP(on-line transaction processing)翻译为联机...
1.sort --排序,很消耗资源 There are a number of different operations that promote sorts: (1)order by clauses (2)group by (3)sort merge join –-这三个会产生排序运算 2.filter --过滤,如not in、min函数等容易产生 Has a number of different meanings, used to indicate partition elimination, ...
Number of sort operations that were performed completely in memory and did not require any disk writes You cannot do much better than memory sorts, except maybe no sorts at all. Sorting is usually caused by selection criteria specifications within table join SQL operations. Sorts(disk): 在磁盘...
2、先执行 EXPLAIN PLAN FOR select * from tableA where paraA=1,再 select * from table(DBMS_XPLAN.DISPLAY)便可以看到oracle的执行计划了,看到的结果和1中的一样,所以使用工具的时候推荐使用1方法。 注意:PL/SQL Dev工具的Command window中不支持set autotrance on的命令。还有使用工具方法查看计划看到的信...
SQL>select * from table(dbms_xplan.display); PLAN_TABLE_OUTPUT --- Plan hash value: 3458767806 --- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ---
SQL>SELECT plan_table_output FROM TABLE(DBMS_XPLAN.DISPLAY('PLAN_TABLE'));示例:SQL> EXPLAIN PLAN FOR SELECT * FROM DAVE;已解释。SQL> SELECT plan_table_output FROM TABLE(DBMS_XPLAN.DISPLAY('PLAN_TABLE'));或者:SQL> select * from table(dbms_xplan.display);PLAN_TABLE_OUTPUT...
SQL>set autotrace on SQL>select * from dave; ID NAME --- --- 8 安庆 1 dave 2 bl 1 bl 2 dave 3 dba 4 sf-express 5 dmm 已选择8行。 执行计划 --- Plan hash value: 3458767806 --- | Id | Operation | Name | Rows | Bytes | Cost...
SQL>select * from table(dbms_xplan.display); PLAN_TABLE_OUTPUT --- Plan hash value: 3458767806 --- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ---
1.set autotrace on 2.explain plan for sql语句; select plan_table_output from table(dbms_xplan.display()); 3.通过第3方工具,如plsql developer(f5查看执行计划)、toad等; 三、看懂执行计划 1.执行计划中字段解释 SQL> select * from scott.emp a,scott.emp b where a.empno=b.mgr; ...
Data operations like filter, sort, or aggregation In addition to the row source tree, the plan table contains information about the following: Optimization, such as the cost and cardinality of each operation Partitioning, such as the set of accessed partitions Parallel execution, such as the...