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SQLite REPLACE Statement

Summary: in this tutorial, you will learn how to use the SQLite REPLACE statement to insert or replace the existing row in a table.

Introduction to the SQLite REPLACE statement

The idea of the REPLACE statement is that when a UNIQUE or PRIMARY KEY constraint violation occurs, it does the following:

• First, delete the existing row that causes a constraint violation.
• Second, insert a new row.

In the second step, if any constraint violation e.g., NOT NULL constraint occurs, the REPLACE statement will abort the action and roll back the transaction.

The following illustrates the syntax of the REPLACE statement.

Or in a short form:

Let’s take a look at some examples of using the SQLite REPLACE statement to understand how it works.

The SQLite REPLACE statement examples

First, create a new table named positions with the following structure.

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Second, insert some rows into the positions table.

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Third, verify the insert using the following SELECT statement.

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The following statement creates a unique index on the title column of the positions table to ensure that it doesn’t have any duplicate position title:

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Suppose, you want to add a position into the positions table if it does not exist, in case the position exists, update the current one.

The following REPLACE statement inserts a new row into the positions table because the position title Full Stack Developer is not in the positions table.

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You can verify the REPLACE operation using the SELECT statement.

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See the following statement.

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First, SQLite checked the UNIQUE constraint.

Second, because this statement violated the UNIQUE constraint by trying to add the DBA title that already exists, SQLite deleted the existing row.

Third, SQLite inserted a new row with the data provided by the REPLACE statement.

Notice that the REPLACE statement means INSERT or REPLACE, not INSERT or UPDATE.

See the following statement.

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What the statement tried to do is to update the min_salary for the position with id 2, which is the developer.

First, the position with id 2 already exists, the REPLACE statement removes it.

Then, SQLite tried to insert a new row with two columns: ( id, min_salary). However, it violates the NOT NULL constraint of the title column. Therefore, SQLite rolls back the transaction.

If the title column does not have the NOT NULL constraint, the REPLACE statement will insert a new row whose the title column is NULL.

In this tutorial, we have shown you how to use the SQLite REPLACE statement to insert or replace a row in a table.

출처 : https://www.sqlitetutorial.net/sqlite-replace-statement/