How to Efficiently Update or Insert Data in SQL Based on Record Existence?

Efficiently manage data based on whether the record exists: IF EXISTS updates, otherwise inserts

Introduction

In SQL, interacting with existing data is a common task. Developers often need to conditionally update or insert data based on whether a record exists. This article aims to address the challenges users face when trying to implement IF EXISTS UPDATE and ELSE INSERT INTO functionality.

IF EXISTS statement

IF EXISTS statement allows developers to specify conditions to check before executing SQL queries. If the condition evaluates to true, the specified action is performed; otherwise, the action is skipped.

Use IF EXISTS for conditional updates and inserts

The question asked in the query involves updating a record if it exists and inserting a new record if it does not exist. To do this, the following steps must be taken:

1. Create a unique constraint: Ensure that the column used to check for the presence of a value has a unique constraint. This prevents duplicate recording and ensures correct data integrity.
2. Using INSERT ... ON DUPLICATE KEY UPDATE: The INSERT ... ON DUPLICATE KEY UPDATE statement combines insert and update operations. If a record with the specified key value already exists, the update clause is executed. Otherwise, the insert clause is used to create a new record.

The correct syntax of this statement is as follows:

<code class="language-sql">INSERT INTO 表名 (列1, 列2, ...)
VALUES (?, ?, ...)
ON DUPLICATE KEY UPDATE
  列1 = VALUES(列1),
  列2 = VALUES(列2),
  ...</code>

Code Example

Use the example provided in the query:

<code class="language-sql">ALTER TABLE subs ADD UNIQUE (subs_email);

INSERT INTO subs (subs_name, subs_email, subs_birthday)
VALUES (?, ?, ?)
ON DUPLICATE KEY UPDATE
  subs_name     = VALUES(subs_name),
  subs_birthday = VALUES(subs_birthday);</code>

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