The syntax for a nested FOR LOOP statement in PL/SQL is as follows −FOR counter1 IN initial_value1 .. final_value1 LOOP sequence_of_statements1 FOR counter2 IN initial_value2 .. final_value2 LOOP sequence_of_statements2 END LOOP; END LOOP; The syntax for a nested WHILE LOOP ...
使用hint 让 sql 语句通过 nested loop 连接, 并且指定 t3 为驱动表 1SQL>select/*+ leading(t3) use_nl(t4)*/*fromt3, t422wheret3.id=t4.t3_idandt3.n=1100;3410rows selected.56SQL>select*fromtable(dbms_xplan.display_cursor(null,null,'allstats last'));78PLAN_TABLE_OUTPUT9---10SQL_ID 8...
正如我之前的博文https://blog.jooq.org/oracle-scalar-subquery-caching/,Oracle 11已经引入了一个标量子查询缓存的特性,可以在jOOQ中激活,避免代价高昂的PL/SQL上下文切换。 enable_memoize在PostgreSQL嵌套循环join中非常有用,参考上述推文,lateral join通常由嵌套循环连接来执行。 开启/关闭该参数 创建一个schema: ...
PL/SQL过程已成功完成。 SYS@vbox66in>insertintotest12selectrownum,rownum,dbms_random.string('a',50)fromdual3connectbylevel<=1004orderbydbms_random.random; 已创建100行。 SYS@vbox66in>SYS@vbox66in>insertintotest22selectrownum,rownum,rownum,dbms_random.string('a',50)fromdual3connectbylevel<=1000...
正如我之前的博文https://blog.jooq.org/oracle-scalar-subquery-caching/,Oracle 11已经引入了一个标量子查询缓存的特性,可以在jOOQ中激活,避免代价高昂的PL/SQL上下文切换。 enable_memoize在PostgreSQL嵌套循环join中非常有用,参考上述推文,lateral join通常由嵌套循环连接来执行。
in the Nested Loop Join series (Introduction to a Nested Loop Join in SQL Server, Parallel Nested Loop Joins – the inner side of Nested Loop Joins and Residual Predicates) in which we will try to understand the Batch Sort, Explicit Sort and some interesting facts about Nested Loop Join. ...
Simple Nested Loop Join:外表每次读一行,去内表比较,外表再找一条(官方好像没有这个) Blocked Nested Loop Join:每次外表读一个块大小的行(多条),默认1000条,扫右表 Index Nested Loop Join :外表读一行,用索引和内表比较,外表再找一条…… Mysql NLJ优化算法参考(没看) ...
Implicit Batch Sort and Nested Loop operator Let’s examine the Nested Loop operator details. You may notice the Optimized property set to true. That is not very informative, what does it mean –“optimized”. Luckily, we have an explanation in the Craig Freedman’s blog for Nested Loop: ...
实际运行一下: 建表: postgres=# CREATE TEMPORARY TABLE sample1 (id, junk) AS postgres-# SELECT oid, repeat('x',250) postgres-# FROM pg_proc postgres-# ORDER BY random(); -- add rowsinrandom order; SELECT2491postgres=# postgres=# CREATE TEMPORARY TABLE sample2 (id, junk) AS ...
PLSQL collection 示例 之 Nested Tables CREATE TABLE Person (Id int, Name varchar(255)); BEGIN FOR i IN 1..4 LOOP insert into person values(i,’abc’||i); END LOOP; commit; END; DECLARE CURSOR cursor_person is SELECT name FROM person;...