理论上来说,嵌套循环连接等于两个嵌套的循环,比如说employees表和departments表之间的嵌套循环连接,可以看成是: FOR erow IN (select * from employees where X=Y) LOOP FOR drow IN (select * from departments where erow is matched) LOOP output values from erow and drow END LOOP END LOOP 可以看出,外...
5.3 merge sort join createindexidx_t1_idont1(id); select/*+ ordered use_merge(t2)*/*fromt1, t2wheret1.id=t2.t1_idandt1.n=19; Oracle 10g版本,在连接条件建立索引可以消除merge sort join表连接的一张表的排序操作。(虽然在两张表的连接条件都建立了索引,却只能消除一张表的排序操作) 注:本文...
用sys用户运行脚本ultxplan.sql 建立这个表的脚本是:rdbms\admin)ultxplan.sql。 SQL> connect sys/sys@colm2 as sysdba; SQL> @rdbms\admin\utlxplan.sql; SQL> create public synonym plan_table for plan_table;--建立同义词 SQL> grant all on plan_table to public;--授权所有用户 要在数据库中建立...
hash join 哈希连接(原理): 表T1和T2在施加了目标SQL中指定的谓词条件(如果有的话)后得到的结果集中数据量较小的那个结果集(S)会被Oracle选为哈希连接的驱动结果集,T2所对应的结果集的数据量相对较大,我们记为B;S是驱动结果集,B是被驱动结果集;接着Oracle会遍历S,读取S中的每一条记录,并对S中的每一条记...
Loops with PL/SQL Types of loops Basic loop loop /* statements */ end loop; While loop while a > b loop /* statements */ end loop See also Iterating over collection variables. For loop for i in 1..1000 loop insert into a values(i,i*2); ...
This is the quickest access method available.Oracle retrieves the specified block and extracts the rows it is interested in. --Rowid扫描是最快的访问数据方式 七、运算符 1.sort --排序,很消耗资源 There are a number of different operations that promote sorts: ...
Name CTL-08: Scan collections using FIRST, LAST, and NEXT in loops. Synopsis A collection in PL/SQL is like a single-dimensional array. A collection differs from an array, however, in that … - Selection from Oracle PL/SQL Best Practices [Book]
“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...
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'INSERT INTO courts.20100625 (idtime, time, court) VALUES ('6002', ' at line 2) Any idea what I'm doing wrong here?Navigate...
The first step in creating a cursor in SQL Server is to choose which method to use. Programmers create cursors in SQL Server either by using the T-SQL language, or via the database’s application-programming interface. In either case, the steps are similar and only the syntax differs. ...