mysql数据库的配置参数log_queries_not_using_indexes的作用是控制未使用索引的查询是否写入慢日志。 背景 在一次项目上线后,监控平台马上收到大量报警。报警内容均是业务存在大量慢sql。将报警sql取出进行分析,发现这些sql运行效率并不低。经过排查因为这些sql在执行过程中未使用到索引,被记录到slow log中。该行
但对于一些特定的SQL语句情况,需要交集优化器选项。 测试当中,发现条件语句里不管有多少个索引可用,intersect 只选择2个索引; 如上案例,建议是联合索引方式。 通过intersect分析,MySQL完全可实现intersect语法的支持,希望后续8.0版本里把这部分加进去。 参考:https://stackoverflow.com/questions/4526686/why-would-mysql...
T-SQL Script to Create All SQL Server Indexes This T-SQL code is designed to generate a script to create all regular non-unique indexes in a specific SQL Server database. This code queries the index metadata by using four views: sys.tables, sys.indexes, sys.index_columns and sys.col...
Partitioned Tables and Indexes in SQL Server 2005 Performance Optimizations for the XML Data Type in SQL Server 2005 Processing XML Showplans Using SQLCLR in SQL Server 2005 Reducing Database Size by Using Vardecimal Storage Format Report Design Tips and Tricks Reporting Services SharePoint Integratio...
Oracle internally creates unique index to prevent duplication in the column values.Indexes would be discussed later in PL/SQL.Syntax:Column level:COLUMN [data type] [CONSTRAINT <constraint name> PRIMARY KEY]Table level:CONSTRAINT [constraint name] PRIMARY KEY [column (s)] The...
The Performance Schema tables do not have any indexes, so the query will need to examine the cross product: MySQL mysql> EXPLAIN SELECT ... <original view definition>\G *** 1. row *** id 1 select_type: SIMPLE table: pst type: ALL possible_keys: NULL key: NULL key_len: NULL ...
SQL Server 2008 supports both row and page compression for both tables and indexes. For information about replication support for compressed data, see "How Compression Affects Replication" in Creating Compressed Tables and Indexes. Restoring a Replicated Database from an Earlier Version You can keep ...
This program illustrates how to use secondary indexes in the NDB API. The source code for this example may be found in the NDB Cluster source tree, in storage/ndb/ndbapi-examples/ndbapi_simple_index/main.cpp. Note This file was previously named ndbapi_simple_index.cpp. The...
1.3.2 SQL Tables A database can be made up of one or more database files or catalogs in ODBC and SQL-92. The fundamental unit of storage in SQL is a table consisting of rows of data organized in columns. All database objects, including tables, views, and indexes, are owned by a...
SQL indexes can be created using WHERE selection predicates. These indexes can also be referred to as sparse indexes. The advantage of a sparse index is that fewer entries are maintained in the index. Only those entries matching the WHERE selection criteria are maintained in the index. In ...