SQL语句 select*from_orderwhereshop_id=1andorder_statusin(1,2,3)orderbycreated_atdesclimit10 in查询在MySQL底层是通过n*m的方式去搜索,类似union,但是效率比union高。in查询在进行cost代价计算时(代价 = 元组数 * IO平均值),是通过将in包含的数值,一条条去查询获取元
) 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__(...
默认值为OFF“超大规模”Azure SQL 数据库除外。 对于“超大规模”中的所有索引生成作,除非使用可恢复索引生成,否则始终 SORT_IN_TEMPDBON。 对于可恢复索引生成,SORT_IN_TEMPDB 始终OFF。 ON 用于生成索引的中间排序结果存储在其中 tempdb。 这可以减少创建索引所需的时间。 但是,这会增加索引生成期间所使用的磁盘...
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...
八、索引和sql语句的优化 1、前导模糊查询不能使用索引,如name like ‘%静’ 2、Union、in、or可以命中索引,建议使用in 3、负条件查询不能使用索引,可以优化为in查询,其中负条件有!=、<>、not in、not exists、not like等 4、联合索引最左前缀原则,又叫最左侧查询,如果在(a,b,c)三个字段上建立联合索引...
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 helped...
Add Time in SQL HH:MM:SS to another HH:MM:SS Adding a column to a large (100 million rows) table with default constraint adding a extra column in a pivot table created uisng T-SQL Pivot Table query Adding a partition scheme to an existing table. Adding a Value to a 'date' Column...
The SQL query below shows a list of tables sorted by the largest tables first. For each table, the indexes in the table are shown. For each index it shows when the index was last used. The query is designed to collect various pieces of information in one place, and give...
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...
Example The following example creates a unique index on the MyCustomers table. Copy CREATE TABLE MyCustomers (CustID int, CompanyName nvarchar(50)); CREATE UNIQUE INDEX idxCustId ON MyCustomers (CustId); Concepts Query Performance Tuning (SQL Server Compact) Database ObjectsEnglish...