How Can I Simulate an Upsert Operation in Microsoft Access Using SQL Queries?

Use simulated query to perform Upsert operation in Microsoft Access

In Microsoft Access, the Upsert operation (update row if it exists, insert row if it does not exist) can be simulated using UPDATE query combined with LEFT JOIN. This approach allows a single query to handle both cases.

To perform an Upsert operation, follow these steps:

1. Create an UPDATE query to set the desired values ​​for columns in existing rows:

<code class="language-sql">UPDATE ... SET <column1> = <value1>, <column2> = <value2>, ... WHERE <key_column> = <key_value></code>

2. Use LEFT JOIN to join an UPDATE query with a temporary table or subquery containing the new values:

<code class="language-sql">UPDATE b
LEFT JOIN a ON b.id = a.id
SET a.f1 = b.f1, a.f2 = b.f2, a.f3 = b.f3</code>

In this example, table b represents the source of the new values ​​and table a represents the target table. LEFT JOIN pairs matching rows from two tables based on a common column id.

This combined query will first try to update existing rows in table a whose id column matches table b. If no matching row is found in table a, the new value is inserted as a new row.

Alternatively, you can use the following query form for easier understanding:

<code class="language-sql">UPDATE main_table
RIGHT JOIN new_data ON main_table.id = new_data.id
SET
main_table.id = new_data.id,
main_table.col_1 = new_data.col_1,
main_table.col_2 = new_data.col_2</code>

This emulates Upsert behavior by first trying to update the row and inserting a new row if the join does not match any existing row in main_table.

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