Oracle uses merge to update or insert data (Summary)

Oracle uses merge to update or insert data (Summary) under Java code summary. Using merge is much faster than traditional first judgment and then selecting insert or update. 1) The main function is to UPDATE and insert data to the database table conditionally. If this row exists, perform an UPDATE operation. If it is a new row, execute the INSERT operation-avoid separate updates-improve performance and ease of use-the syntax of the MERGE statement is as follows: MERGE [hint] INTO [schema.] table [t_alias] USING [schema.] {table | view | subquery} [t_alias] ON (condition) when matched then merge_update_clause when not matched then merge_insert_clause; let's check the example to find out what is going ON: merge into copy_emp c USING employees e ON (c. employee_ I D = e. employee_id) when matched then update set c. first_name = e. first_name, c. last_name = e. last_name, c. department_id = e. department_id when not matched then insert values (e. employee_id, e. first_name, e. last_name, e. email, e. phone_number, e. hire_date, e. job_id, e. salary, e. commission_pct, e. manager_id, e. metn_id); merge into copy_emp c USING employees e ON (c. employee_id = e. employee_id) WHEN MATCHED THEN Update set c. first_name = e. first_name, c. last_name = e. last_name, c. department_id = e. department_id when not matched then insert values (e. employee_id, e. first_name, e. last_name, e. email, e. phone_number, e. hire_date, e. job_id, e. salary, e. commission_pct, e. manager_id, e. metn_id); 3) Use merge Note: CREATE a test TABLE: create table mm (id number, NAME VARCHAR2 (20); create table mn (id number, NAME VARCHAR2 (20); insert data IN Sert into mm values (1, 'A'); insert into mn values (1, 'B'); execute: merge into mn a using mm B ON (. ID = B. ID) when matched then update set. ID = B. id when not matched then insert values (B. ID, B. NAME); ON (. ID = B. ID) error is reported because the field used by the on clause cannot be used for update, that is, Oracle cannot update the Column Used for connection modification: merge into mn a using mm B ON (. ID = B. ID) when matched then update set. NAME = B. name when not matched then insert values (B. ID, B. NAME ); ON (. ID = B. ID) www.2cto.com INSERT: insert into mm values (1, 'C'); then execute: merge into mn a using mm B ON (. ID = B. ID) when matched then update set. NAME = B. name when not matched then insert values (B. ID, B. NAME); ON (. ID = B. an error is reported because a group of stable rows www.2cto.com 4 in the source table cannot be obtained.) update the data of the same table. Pay attention to the following details. Because the using dataset may be null, use the count () function. Merge into mn a USING (select count (*) co from mn where mn. ID = 4) B ON (B. co <> 0) -- count and <> are used here. Pay attention to why! When matched then update set a. NAME = 'E' where a. ID = 4 when not matched then insert values (4, 'E ');