insert first&insert all的区别

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：（占不考虑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

 

部分转载自：http://lanying1982.blog.163.com/blog/static/23067748200810122341539/