Introduction to Oracle merge into

 

In the common operations of the Oracle database, sometimes it is necessary to use the B table to update the content in the A table. One method is to use update to associate two tables to update, and another method is to use merge into.

 

Merge into a statement can realize the functions of update and insert, and it is more efficient

grammar

 

MERGE INTO [your table-name] [rename your table here]

USING ( [write your query here] )[rename your query-sql and using just like a table]

ON ([conditional expression here] AND [...]...)

WHEN MATHED THEN [here you can execute some update sql or something else ]

WHEN NOT MATHED THEN [execute something else here ! ]

 

 

Example 

Create table test_sj_salary, insert sample data

 

create table test_sj_salary
(
   id integer primary key,
   name varchar2(100),
   salary integer
);

truncate table test_sj_salary;

insert into test_sj_salary (ID, NAME, SALARY)
values ​​(1, 'Zhang San', 5000);

insert into test_sj_salary (ID, NAME, SALARY)
values ​​(2, 'Li Si', 4000);

insert into test_sj_salary (ID, NAME, SALARY)
values ​​(3, 'Wang Wu', 6000);

insert into test_sj_salary (ID, NAME, SALARY)
values ​​(4, 'Li Liu', 3500);

commit;

 

Build test_sj_cp, insert sample data

create table test_sj_cp
(   
   id integer primary key,   
   name varchar2(100),   
   salary integer  
);

truncate table test_sj_cp;

insert into test_sj_cp (ID, NAME, SALARY)   
values ​​(9, 'Zhang San', 9000);   
  
insert into test_sj_cp (ID, NAME, SALARY)   
values ​​(10, 'Li Si', 10000);   
  
insert into test_sj_cp (ID, NAME, SALARY)   
values ​​(11, 'Wang Ermazi', 11000);

commit;

 

Function to be implemented: use test_sj_cp to update the salary field in test_sj_salary according to the same name

 

Method 1, using the ordinary update method

 

update test_sj_salary a
set a.salary=(select b.salary from test_sj_cp b where b.name=a.name)
where exists (select 1 from test_sj_cp c where c.name=a.name);
commit;

 

Method 2, using the merge into method

merge into test_sj_salary a
using test_sj_cp b
  on (a.name=b.name)
when matched then update set a.salary=b.salary;
commit;

 Isn't it very concise!

 

Extended function, through merge to achieve matching updates, unmatched insert data

 

merge into test_sj_salary a
using test_sj_cp b
  on (a.name=b.name)
when matched then update set a.salary=b.salary
when not matched then insert(id,name,salary) values(b.id,b.name,b.salary);
 
commit;