PL/SQL Nested Table Using Initialized Values To get started using a Nested Table, create a code block that declares a nested table type and instantiates a nested table of this created type (Lines 2 & 4). This code iterates through a FOR Loop 3 times to show that the Nested Table has ...
关于:Block Nested-Loop Join,是Nested-Loop Join的一种优化,叫缓存块嵌套循环连接,缓存嵌套循环连接是通过一次性缓存多条数据,把参与查询的缓存的列缓存到join buffer中,然后拿join buffer里面的数据匹配和内层数据进行匹配,从而减少内层循环的次数。 先简单看下join buffer 说明 join buffer size默认是256k,可以配置...
Block Nested-Loop Join算法: BNL算法原理:将外层循环的行/结果集存入join buffer,内存循环的每一行数据与整个buffer中的记录做比较,可以减少内层循环的扫描次数。 通过EXPLAIN发现,extra中有数据是Using join buffer (Block Nested Loop);一般多表关联查询会有这种算法,优化方式就是在关联条件字段上加上索引。 导致关...
【MySQL】mysql因为字符集导致left join出现Using join buffer (Block Nested Loop) 今天在查询一个sql的时候发现没有使用到索引 仔细看了很多遍,该加的索引都加了,还是不行 使用explain查看 索引为什么失效 隐式转换导致索引失效 随着表的增长,where条件出来的数据太多,大于15%,使得索引失效(会导致CBO计算走索引花费...
Execute the following two PL/SQL blocks, and explain why they produce different output for the same value of the variablev_num. Remember to issue the SET SERVEROUTPUT ON command before running this script. -- Block 1 DECLARE v_num NUMBER := NULL; ...
SQL> select (select pval1 from sys.aux_stats$ where pname = 'IOSEEKTIM') + 2 (select value from v$parameter where name = 'db_file_multiblock_read_count') * (select value from v$parameter where name = 'db_block_size') / (select pval1 from sys.aux_stats$ where pname = 'IOTFR...
Block Cache:块缓存 基线SSTable(ROS):转储经过一定条件会放到基线SSTable中,基线会在空闲时间进行压缩,看起来压缩的策略是size-tieredleveled SQL引擎 这次基本不涉及到sql解析的工作,但是根据官方说明,这次第一名的老哥是优化了SQL层的,目测是在SQL层加了个Map存储结果(理论属于作弊行为?,麻) ...
Scans all the block in the index, Rows are not returned in sorted order, Introduced in 7.3 and requires V733_PLANS_ENABLED=TRUE and CBO, may be hinted using INDEX_FFS hint, uses multiblock i/o, can be executed in parallel, can be used to access second column of concatenated indexes. ...
指在function,procedure等subprograms中对事务进行自治管理,当在别的pl/sql block里去调用这些subprograms的时候这些subprograms并不随着父pl/sql block的失败而回滚,而是自己管自己commit。以Commit作为事务的结束。自治事务常用于写入LOG或TRAC信息便于查找错误。
“Unable to enlist in the transaction” with Oracle linked server from MS SQL Server [<Name of Missing Index, sysname,>] in non clustered index [Execute SQL Task] Error: The value type (__ComObject) can only be converted to variables of type Object. [ODBC Driver Manager] Data source nam...