SQL 执行计划简介 执行计划算子 TABLE SCAN TABLE LOOKUP JOIN COUNT GROUP BY WINDOW FUNCTION SUBPLAN FILTER DISTINCT SEQUENCE MATERIAL SORT LIMIT FOR UPDATE SELECT INTO SUBPLAN SCAN UNION INTERSECT EXCEPT/MINUS INSERT DELETE UPDATE MERGE EXCHANGE GI 执行计划缓存 快速参数化 实时执行计划展示 分布式执行计划 SQL 优化
Fastest table sort in the West - Redesigning DuckDB’s sort DuckDB作为业界一流的数据库,在Sort执行上有着与众不同的实现方式 DuckDB逆天的排序性能 DuckDB的排序主要有以下特性 Binary String Comparison Radix Sort Two-Phase Parallel Sorting External Sorting Tips: 本文目前仅对前两项进行分析 Binary String ...
可能是拼写错误或列名不匹配。 使用DESCRIBE table_name;或SHOW COLUMNS FROM table_name;查看表的结构,确认列名是否存在。 修改SQL 语句: 如果列名确实不存在,需要修改 SQL 语句,使用正确的列名。 例如,假设正确的列名是description,则将sortdesc替换为description: SELECTid, name, description FROM your_table; 添加...
SQL trigger to insert value into same row with value from another table on insert or update When a new record is inserted in dbo.BOM, or when my column BOM.Site is updated, I want to lookup the BOM.Site value in dbo.SiteMap, and bring back the SiteMap.SiteName value and insert it ...
二、in和exists哪个性能更优 sql脚本: /*建库*/createdatabasetestdb6;usetestdb6;/*用户表*/droptableifexistsusers;createtableusers( idintprimarykeyauto_increment, namevarchar(20) );insertintousers(name)values('A');insertintousers(name)values('B');insertintousers(name)values('C');insertintouse...
qSort => std::sort & qSort(list) => std::sort(list.begin, list.end) qStableSort => std::stable_sort & qStableSort(list) => std::stable_sort(list.begin, list.end) qGreater => std::greater qLess => std::less qSwap => std::swap ...
Create Table:CREATETABLE`testsorterr3`(`id`int(11)DEFAULTNULL,`name1`varchar(510)NOTNULL,`name2`varchar(510)NOTNULL,UNIQUEKEY`name1`(`name1`,`name2`))ENGINE=InnoDBDEFAULTCHARSET=utf81rowinset(0.00sec)mysql>selectcount(*)from testsorterr3;+---+|count(*)|+---+|0|+---+1rowinset(...
二、in和exists哪个性能更优 sql脚本: /*建库*/ create database testdb6; use testdb6; /* 用户表 */ drop table if exists users; create table users( id int primary key auto_increment, name varchar(20) ); insert into users(name) values ('A'); ...
Spark SQL可以通过调用sqlContext.cacheTable("tableName") 或者dataFrame.cache(),将表用一种柱状格式( an inmemory columnar format)缓存至内存中。然后Spark SQL在执行查询任务时,只需扫描必需的列,从而以减少扫描数据量、提高性能。通过缓存数据,Spark SQL还可以自动调节压缩,从而达到最小化内存使用率和降低...
Test your SQL performance skills in just three minutes. › Table of Contents Preface Anatomy of an Index The Where Clause Performance and Scalability The Join Operation Nested Loops Hash Join Sort Merge Clustering Data Sorting and Grouping Partial Results Modifying Data Execution Plans Myth Directory...