MySQL inserts data when the record does not exist

In MySQL, inserting a record is very simple, but in some special applications, before inserting a record, you need to check whether the record already 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, supplier_typeFROM suppliersWHERE not exists (select * from clientswhere clients.client_id = suppliers.supplier_id);

Example 2: Insert a single record

Code:

INSERT INTO clients(client_id, client_name, client_type)SELECT 10345, ’IBM’, ’advertising’FROM dualWHERE not exists (select * from clientswhere 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.

Article Reprinted from: http://www.isclassic.net/archives/170

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