Insert when record does not exist and update method when record exists

MySQL inserts a record when the record does not exist. When the record exists, there are three solutions to update the online. Example 1: INSERT multiple records. Suppose There Is A client_id table with the primary key. You can use the following statement: insert into clients (client_id, client_name, client_type) SELECT supplier_id, supplier_name, 'advertising' FROM suppliers www.2cto.com WHERE not exists (select * from clients where clients. client_id = suppliers. supplier_id); Example 1: INSERT a single record insert into clients (client_id, client_name, client_type) SELECT 10345, 'ibm ', 'advertising' FROM dual WHE RE not exists (select * from clients where clients. client_id = 10345); Using dual as the table name allows you to directly keep up with the value of the field to be inserted after the select statement, even if these values do not exist in the current table. Type 2: Use of on duplicate key update in INSERT. If you specify on duplicate key update and INSERT a row, DUPLICATE values will appear in a UNIQUE index or primary key, the old row is updated. For example, if column a is defined as UNIQUE and contains a value of 1, the following two statements have the same effect: mysql> insert into table (a, B, c) VALUES, 3)-> on duplicate key update c = c + 1; mysql> UPDATE table SET c = c + 1 WHERE a = 1; if a row is inserted as a new record, the value of the affected row is 1. If the original record is updated, the value of the affected row is 2. NOTE: If Column B is also a unique column, INSERT is equivalent to this UPDATE statement: mysql> UPDATE table SET c = c + 1 WHERE a = 1 OR B = 2 LIMIT 1; if a = 1 OR B = 2 matches multiple rows, only one row is updated. Generally, you should avoid using the on duplicate key clause for tables with multiple unique keywords. You can use the VALUES (col_name) function in the UPDATE clause to reference the column VALUES from the INSERT section of the INSERT... UPDATE statement. In other words, if there is no duplicate keyword conflict, the VALUES (col_name) in the UPDATE clause can reference the value of the inserted col_name. This function is particularly applicable to multiline inserts. The VALUES () function only makes sense in the INSERT... UPDATE statement. Otherwise, NULL is returned. Example: mysql> insert into table (a, B, c) VALUES (1, 2, 3), (4, 5, 6)-> ON DUPLICATE KEY UPDATE c = VALUES () + VALUES (B); this statement serves the same purpose as the following two statements: www.2cto.com mysql> insert into table (a, B, c) VALUES (, 3) -> on duplicate key update c = 3; mysql> insert into table (a, B, c) VALUES (4, 5, 6)-> ON DUPLICATE KEY UPDATE c = 9; when you use on duplicate key update, the DELAYED option is ignored. Third, we may often encounter this situation when using database REPLACE statements. If a table creates a unique index on a field and inserts a record into the table using an existing key value, a primary key conflict error is thrown. Of course, we may want to overwrite the original record value with the new record value. If you use the traditional method, you must first use the DELETE statement to DELETE the original record, and then use INSERT to INSERT a new record. MySQL provides us with a new solution, which is the REPLACE statement. When you use REPLACE to INSERT a record, if there is no duplicate record, REPLACE is the same as the INSERT function. If there is a duplicate record, REPLACE replaces the original record value with the value of the new record. The biggest advantage of using REPLACE is that you can combine DELETE and INSERT into one to form an atomic operation. In this way, you do not have to consider complicated operations such as adding transactions when using both DELETE and INSERT. When using REPLACE, the table must have a unique index, and the field where the index is located cannot allow null values. Otherwise, REPLACE is exactly the same as INSERT. After REPLACE is executed, the system returns the affected number of rows. If 1 is returned, no duplicate records exist in the table. If 2 is returned, a duplicate record exists, the system automatically calls DELETE to DELETE this record, and then inserts this record with INSERT. If the returned value is greater than 2, multiple unique indexes exist, and multiple records are deleted and inserted. The REPLACE syntax is very similar to INSERT. The following REPLACE statement inserts or updates a record. Replace into users (id, name, age) VALUES (123, 'zhao Benshan ', 50); insert multiple records: replace into users (id, name, age) VALUES (123, 'zhao Benshan ', 50), (134, 'Mary', 15); REPLACE can also be SET statement replace into users SET id = 123, name = 'zhao Benshan ', age = 50; as mentioned above, REPLACE may affect more than three records, because there is more than one unique index in the table. In this case, REPLACE considers each unique index, deletes the duplicate record corresponding to each index, and inserts this new record. Assume that there is a table 1 with three fields a, B, and c. They all have a unique index. Www.2cto.com create table table1 (a int not null unique, B INT NOT NULL UNIQUE, c INT NOT NULL UNIQUE ); assume that three records exist in Table 1, a B c 1 1 1 1 2 2 2 3 3 3 3. Then we use the REPLACE statement to insert a record into table 1. Replace into table1 (a, B, c) VALUES (0.00, 3); The returned results are as follows: Query OK, 4 rows affected (sec) the record in table1 is as follows: a B c 1 2 3. We can see that REPLACE deletes all the three original records and inserts (1, 2, 3. Summary: Although there is no specific test, I feel that the first kind of resource is the most expensive (just feeling), but if you do not have a primary key, you can only use it. The difference between the second and third types is: 1) insert is to try to insert first, and update if the primary key exists. REPLACE tries to insert data first. If the primary key exists, the original record is deleted and then inserted. 2) if multiple unique keywords conflict (conflicts with different keywords occur in different records ), for example, if there are two fields and two records in conflict (no records conflict with one field), insert selects the sorting rule and updates the previous one. REPLACE deletes the two records, insert a new record. If you have any mistakes, please correct me. Author: jipengyun2008