) ENGINE=InnoDB DEFAULT CHARSET=utf8; """# 注意,一次性执行多行sql,必须在连接时,指定client_flag=CLIENT.MULTI_STATEMENTScursor.execute(sql) conn.commit()defgen(num, tmp_list):foriinrange(num): tmp = fk.paragraph()ifrandom.randint(0,1)elsetmp_list[random.randint(0, (tmp_list.__len__(...
9.联表查询的时候,记得把小结果集放在前面,遵循小结构及驱动大结果集的原则,这条很重要! 10.开启慢查询,定期用explain优化慢查询中的SQL语句。 11.任何对列的操作都将导致表扫描,它包括数据库函数、计算表达式等等,查询时要尽可能将操作移至等号右边。 12.IN、OR子句常会使用工作表,使索引失效。如果不产生大量...
1、数据泵在导入时一般情况下只需指定parallel>1即可在创建索引时候使用并行,导入时可以从trace文件中看到数据泵采用并行创建索引; 2、创建索引时并行度可能会等于parallel*2,这是因为oracle产生了两组query slave set,一组用来扫描表,一组用来创建索引; 3、如果数据泵带有sqlfile参数,得到的sql文本中并行度会显示为...
(*) AS COUNT FROM Sales.SalesOrderDetail AS od, Sales.SalesOrderHeader AS o WHERE od.SalesOrderID = o.SalesOrderID GROUP BY OrderDate, ProductID; GO -- Create an index on the view CREATE UNIQUE CLUSTERED INDEX IDX_V1 ON Sales.vOrders (OrderDate, ProductID); GO -- This query can ...
了解SQL执行的线程的状态及消耗的时间。默认是关闭的,开启语句“set profiling = 1;” SHOWPROFILES; SHOWPROFILEFORQUERY#{id}; 4.trace trace分析优化器如何选择执行计划,通过trace文件能够进一步了解为什么优惠券选择A执行计划而不选择B执行计划。 setoptimizer_trace="enabled=on"; ...
sql 语句 代码语言:javascript 代码运行次数:0 运行 AI代码解释 SELECTYEAR,SUBSTRING_INDEX(GROUP_CONCAT(amount),",",1)ASm1,SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(amount),",",2),",",-1)ASm2,SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(amount),",",-2),",",1)ASm3,SUBSTRING_INDEX(GROU...
To see which indexes the query optimizer uses for a specific query, in SQL Server Management Studio, on the Query menu, select Include Actual Execution Plan.Don't always equate index usage with good performance, and good performance with efficient index use. If using an index always help...
SQL העתק FROM SystemIndex A remote query using the FROM clause is shown in the following example. Adding ComputerName transforms the previous example into a remote query.SQL העתק FROM [<ComputerName>.]SystemIndex ...
一、慢SQL优化思路 1、慢查询日志记录慢SQL 如何定位慢SQL呢、我们可以通过慢查询日志来查看慢SQL。默认的情况下呢,MySQL数据库是不开启慢查询日志(slow query log)呢。所以我们需要手动把它打开。 查看下慢查询日志配置,我们可以使用show variables like 'slow_query_log%'命令,如下: ...
For more information, see Optimize index maintenance to improve query performance and reduce resource consumption. REORGANIZE isn't required in order to move the closed delta rowgroups into compressed rowgroups. The background tuple-mover (TM) process wakes up periodically to compress the closed delt...