select * from (select t.*, rownum as rn from t) a where a.rn >= 1 and a.rn <= 10; SELECT * FROM table(dbms_xplan.display_cursor(null,null,'allstats last')); 执行计划分析: | Id | Operation | Name | Starts | E-Rows | A
drop table t purge; create table t as select * from dba_objects; insert into t select * from t; commit; 通过复制dba_objects表并再次插入自身数据,我们得到了一个数据量较大的测试表,为后续的性能对比提供了有效的测试基础。 对比实验:缓存前后的性能差异 语句1:普通查询(首次执行) select count(*) ...
FROM table_name WHERE condition; MySQL 语法: SELECT column_name(s) FROM table_name WHERE condition LIMIT number; Oracle 12 语法: SELECT column_name(s) FROM table_name ORDER BY column_name(s) FETCH FIRST number ROWS ONLY; 旧版Oracle 语法: SELECT column_name(s) FROM table_name WHERE ROWNU...
0 rows affected (0.00 sec) 删除stu表中id值为20到30的数据(等级于上面写法) mysql> delete from stu where id between 20 and 30; Query OK, 0 rows affected (0.00 sec) 删除stu表中id值大于200的数据 mysql> delete from stu where
from_item [ NATURAL ] join_type from_item [ ON join_condition | USING ( join_column [, ...] ) ] 以下小节提供了可在查询中使用的附加子句的详细信息,前提是它们遵循上述格式。 SNAPSHOT子句 此子句可用于基于快照ID增量读取表中的数据。 快照ID是由Long-type数字表示的检查点标记,每次将数据写入到快...
Columnstore supports index defragmentation by removing deleted rows without the need to explicitly rebuild the index. TheALTER INDEX ... REORGANIZEstatement removes deleted rows, based on an internally defined policy, from the columnstore as an online operation ...
CREATE TABLE AS CREATE TABLE PARTITION CREATE TEXT SEARCH CONFIGURATION CREATE TEXT SEARCH DICTIONARY CREATE TRIGGER CREATE TYPE CREATE USER CREATE VIEW CURSOR DISCARD DROP BLOCK RULE DROP DATABASE DROP EXCEPT RULE DROP FOREIGN TABLE DROP FUNCTION DROP GROUP DROP INDEX DROP ...
If the actual number of rows is much higher than the guessed value, performance of downstream operations can suffer.New plans will use the actual cardinality of the table variable encountered on first compilation instead of a fixed guess. For more information, seetable va...
DROP: Drop command is a DDL command. It completely removes a table or database, including its structure and all data from the database. DELETE: Delete is a DML command. It removes specific rows of data from a table based on a given condition. TRUNCATE: Truncate is a DDL Command. It ...
values (3,'Lilei say ''world'''); INSERT 0 1 INSERT INTO tt01 values (4,'Hanmei do 100%'); INSERT 0 1 SELECT * FROM tt01; id | content ---+--- 3 | Lilei say 'world' 4 | Hanmei do 100% 1 | Jack say 'hello' 2 | Rose do 50% (4 rows) DEFAULT 对应字段名的缺省...