How does one run the MySQL database when the record does not exist?

We all know that inserting an insert record in a MySQL database is very simple, but there are special applications. before inserting a record, we need to check whether this record already exists and perform the insert operation only when the record does not exist. This article describes the solution to this problem.

Classification: PHP/MySQL,

Key words: exists, insert, mysql,

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Insert a record in a MySQL database. However, in some special applications, before inserting a record, you must check whether the record exists. The insert operation is performed only when the record does not exist, this article describes the solution to this problem.

Q: I have created a table to store customer information. I know that the insert statement can be used to insert information into the table. But how can I ensure that duplicate records are not inserted?

Answer: You can use the EXISTS condition to prevent duplicate records from being inserted.

Example 1: insert multiple records

Suppose there is a clients table with the primary key of client_id, you can use the following statement:

 
 

  
  
Code:  
  
  
INSERT INTO clients  
  
  
(client_id, client_name, client_type)  
  
  
SELECT supplier_id, supplier_name, 'advertising'  
  
  
FROM suppliers  
  
  
WHERE not exists (select * from clients  
  
  
where clients.client_id = suppliers.supplier_id); 
 
 

Example 1: Insert a single record into the MySQL database

 
 

  
  
Code:  
  
  
INSERT INTO clients  
  
  
(client_id, client_name, client_type)  
  
  
SELECT 10345, 'IBM', 'advertising'  
  
  
FROM dual  
  
  
WHERE not exists (select * from clients  
  
  
where clients.client_id = 10345); 
 
 

Using dual as the table name allows you to directly keep up with the values of the fields to be inserted after the select statement, even if these values do not exist in the current table.