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...
When a view cannot be merged into the main query you will often see a projection view operation. This indicates that the 'view' will be selected from directly as opposed to being broken down into joins on the base tables. A number of constructs make a view non mergeable. Inline views ar...
列 SQL_ID 记录产生等待事件的SQL 语句的 ID,该列可以和 V$SQL 视图结合,以获取存在问题的 SQL 语句。为了方便一个共享用户环境(如 web 应用程序)中的客户端的识别,也显示了 CLIENT_ID 列,这可以由DBMS_SESSION.SET_IDENTIFIER 来设置。 既然ASH 信息这么有价值,那么如果以一种类似于 AWR 的永久方式来保存这...
Partition views are a legacy technology that were superceded by the partitioning option. This section of the article is provided as reference for such legacy systems. 附:oracle优化器(Optimizer) Oracle 数据库中优化器(Optimizer)是SQL分析和执行的优化工具,它负责指定SQL的执行计划,也就是它负责保证SQL执...
projection VARCHAR(4000), special_predicates VARCHAR(4000), time INT, qblock_name VARCHAR(128), other_xml VARCHAR(4000)); Query OK, 0 rows affected obclient> CREATE TABLE t1(c1 INT); Query OK, 0 rows affected /* Explain an SQL query and store the obtained execution plan in the test ...
>>Note the drop-down control added to the Explain Plan button in the worksheet toolbar. This is a total disaster. Please make an option to disable this “feature” or just disable it. This “feature” blocks using dbms_xplan. I typically use gather_plan_statistics hint and select * fro...
Difficult to interpret, isn’t it? You want it to be properly formatted to be readable. DBMS_XPLAN does it for you. SQL> set linesize 132; SQL> SELECT * FROM TABLE(dbms_xplan.display); PLAN_TABLE_OUTPUT --- --- Plan hash value: 2872589290 ---...
Fill in the blank. When using information from a database, programmers often store the information from the database ___. Write SQL statements to add these 3 new rows to the PET_OWNER table. Assume that OwnerID is a surrogate key and the DBMS ...
12.1.3.1 Using V$SQL_PLAN Views In addition to running the EXPLAIN PLAN command and displaying the plan, you can use the V$SQL_PLAN views to display the execution plan of a SQL statement: After the statement has executed, you can display the plan by querying the V$SQL_PLAN view. V$SQL...
Oracle10g\11g中,如果我们对目标SQL执行explain plan命令,则oracle就将解析目标SQL所产生的执行计划的具体执行步骤写入PLAN_TABLE,随后执行select∗fromtable(dbmsxplan.display),只是从PLANTABLE,随后执行select∗fromtable(dbmsxplan.display),只是从PLANTABLE中将这些具体执行步骤以格式化的方式显示出来。