Oracle 变量绑定与变量窥视合集系列三
三用示例演示一次分析，多次执行的示例，并对给出演示结果我们分别演示硬解析 软解析 执行不同组合
实验
没有绑定变量
LEO1@LEO1> drop table leo3 purge; 清理环境
Table dropped.
LEO1@LEO1> drop table leo4 purge;
Table dropped.
LEO1@LEO1> drop table leo5 purge;
Table dropped.
LEO1@LEO1> create table leo3 as select * from dba_objects; 创建三张表
Table created.
LEO1@LEO1> create table leo4 as select * from dba_objects;
Table created.
LEO1@LEO1> create table leo5 as select * from dba_objects;
Table created.
LEO1@LEO1> select object_type from leo3 where object_id=100; 执行4次
OBJECT_TYPE
-------------------
EDITION
LEO1@LEO1> select object_type from leo3 where object_id=200;
OBJECT_TYPE
-------------------
INDEX
LEO1@LEO1> select object_type from leo3 where object_id=300;
OBJECT_TYPE
-------------------
TABLE
LEO1@LEO1> select object_type from leo3 where object_id=400;
OBJECT_TYPE
-------------------
TABLE
LEO1@LEO1> select sql_text,parse_calls,loads,executions from v$sql where sql_text like 'select object_type from leo3 where %' order by 1;
SQL_TEXT PARSE_CALLS LOADS EXECUTIONS
-------------------------------------------------- ----------- ---------- ----------
select object_type from leo3 where object_id=100 1 1 1
select object_type from leo3 where object_id=200 1 1 1
select object_type from leo3 where object_id=300 1 1 1
select object_type from leo3 where object_id=400 1 1 1
从视图上可以看出oracle认为这4条sql语句是完全不一样的，每执行一遍，都需要做一次硬解析。
绑定变量1
LEO1@LEO1> variable leo number; 定义变量
LEO1@LEO1> execute :leo:=100; 变量赋值 leo=100
PL/SQL procedure successfully completed.
LEO1@LEO1> select object_type from leo4 where object_id=:leo; 引用这个变量
OBJECT_TYPE
-------------------
EDITION
LEO1@LEO1> execute :leo:=200; 变量赋值 leo=200
PL/SQL procedure successfully completed.
LEO1@LEO1> select object_type from leo4 where object_id=:leo; 引用这个变量
OBJECT_TYPE
-------------------
INDEX
LEO1@LEO1> execute :leo:=300; 变量赋值 leo=300
PL/SQL procedure successfully completed.
LEO1@LEO1> select object_type from leo4 where object_id=:leo; 引用这个变量
OBJECT_TYPE
-------------------
TABLE
LEO1@LEO1> execute :leo:=400; 变量赋值 leo=400
PL/SQL procedure successfully completed.
LEO1@LEO1> select object_type from leo4 where object_id=:leo; 引用这个变量
OBJECT_TYPE
-------------------
TABLE
LEO1@LEO1> select sql_text,parse_calls,loads,executions from v$sql where sql_text like 'select object_type from leo4 where %' order by 1;
SQL_TEXT PARSE_CALLS LOADS EXECUTIONS
-------------------------------------------------- ----------- ---------- --------------- ----------- ---------- --------------
select object_type from leo4 where object_id=:leo 4 1 4
SQL_TEXT：我们跟踪的sql语句
PARSE_CALLS：硬解析+软解析次数 其中硬解析1次+3次软解析
LOADS：硬解析次数 1次
EXECUTIONS：执行次数 4次
绑定变量：
Oracle认为这4条SQL是完全一样的（除了谓词部分）所以第一次执行的时候做一次硬解析后续3条SQL只做软解析，比上一个少了三次硬解析，性能提高
绑定变量2
LEO1@LEO1> begin
for leo in 1..4 loop
execute immediate 'select object_type from leo5 where object_id=:leo' using leo;
end loop;
end;
/
PL/SQL procedure successfully completed.
LEO1@LEO1> select sql_text,parse_calls,loads,executions from v$sql where sql_text like 'select object_type from leo5 where %' order by 1;
SQL_TEXT PARSE_CALLS LOADS EXECUTIONS
-------------------------------------------------- ----------- ---------- --------------- ----------- ---------- --------------
select object_type from leo5 where object_id=:leo 1 1 4
绑定变量：
Oracle认为这4条SQL是完全一样的（除了谓词部分），和上面不同的是只做了1次硬解析没有软解析，反复执行了4次。我们做了一个循环，用leo变量代替谓词常量，每次都用相同的执行计划（执行计划不需要重新生成），只是改变一下常量值而已。
Leonarding
2013.2.3
天津&winter
分享技术~成就梦想
Blog：www.leonarding.com
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