【转】insert first&insert all的区别 ---OCP--047--170

insert first/all

 

利用insert first/all使得INSERT语句可以同时插入多张表，还可以根据判断条件来决定每条记录插入到哪张或哪几张表中。

insert first/all语法 
[ ALL | FIRST ] 
WHEN condition THEN insert_into_clause [values_clause] 
[insert_into_clause [values_clause]]... 
[WHEN condition THEN insert_into_clause [values_clause] 
[insert_into_clause [values_clause]]... 
]... 
[ELSE insert_into_clause [values_clause] 
[insert_into_clause [values_clause]]... 
] 

insert first/all 是对每一行来进行判断
两者区别：
insert first：对于每一行数据，只插入到第一个when条件成立的表，不继续检查其他条件。
insert all ：对于每一行数据，对每一个when条件都进行检查，如果满足条件就执行插入操作。

create table test_a(a number,b number);
create table b as select * from test_a;
create table c as select * from test_a;


insert into test_a values(1,0);
insert into test_a values(1,1);
insert into test_a values(1,2);
insert into test_a values(2,0);
insert into test_a values(3,0);

SQL> select * from test_a;

         A          B
---------- ----------
         1          0
         1          1
         1          2
         2          0
         3          0
         
现分别对insert first和insert all语句进行简单测试：（暂不考虑SQL是否具有真实作用）      


SQL> insert all
  2  when a=1 then  into b
  3  when a=1 then  into c
  4  select * from test_a; 

6 rows created.

Elapsed: 00:00:00.01
SQL> select * from b;

         A          B
---------- ----------
         1          0
         1          1
         1          2

3 rows selected.

Elapsed: 00:00:00.00
SQL> select * from c;

         A          B
---------- ----------
         1          0
         1          1
         1          2

3 rows selected.

Elapsed: 00:00:00.01
SQL> rollback;

Rollback complete.

Elapsed: 00:00:00.01
SQL> select * from b;

no rows selected

Elapsed: 00:00:00.00
SQL> select * from c;

no rows selected

Elapsed: 00:00:00.00
SQL> insert first
  2  when a=1 then  into b
  3  when a=1 then  into c
  4  select * from test_a;    

3 rows created.

Elapsed: 00:00:00.00
SQL> 
SQL> select * from b;

         A          B
---------- ----------
         1          0
         1          1
         1          2

3 rows selected.

Elapsed: 00:00:00.00
SQL> select * from c;

no rows selected

Elapsed: 00:00:00.00