How Can I Efficiently Insert and Update Rows in MySQL Using Composite Keys and ON DUPLICATE KEY?

MySQL: Using ON DUPLICATE KEY with Composite Columns

When working with tables that lack a unique column, performing efficient inserts and updates can be challenging. One solution is to utilize MySQL's ON DUPLICATE KEY clause, which allows for conditional updates based on a specified key.

In the case of a table with a combination of col_1 and col_2 values serving as a unique identifier, an ON DUPLICATE KEY query can be constructed using a composite key. By creating a PRIMARY or UNIQUE index on both columns, you can enable the use of this clause.

// create a composite index
CREATE INDEX my_composite_index ON my_table (column1, column2);

// insert or update using ON DUPLICATE KEY
INSERT INTO my_table (column1, column2, column3) VALUES ('value1', 'value2', 'value3') ON DUPLICATE KEY UPDATE column3=column3+1;

This query will insert a new row if the combination of col_1 and col_2 values does not already exist. If a matching row is found, it will update the value of column3 by incrementing it by 1.

By employing composite keys in conjunction with ON DUPLICATE KEY, you can achieve efficient conditional updates and inserts, even in the absence of a single unique column.

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