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Emmanouil Liakos
Emmanouil Liakos

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Quick post about the SQLite UPSERT and the new RETURNING clause.

The RETURNING clause

You can read the official docs here.

Many times we find ourselves wanting to return some data (probably the id) after inserting records in our database. Since version 3.35.0 (2021-03-12), SQLite supports the RETURNING clause, which allows you to return a result row (or specific columns) for each modified database row by a DELETE, UPDATE or INSERT statement.

INSERT INTO customers (fullName, birthdateTimestamp, address) 
VALUES ('Andrew Mitch', 643911868, '206 Grange Road, Gillingham') 
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The above query, after execution, will return us every value inserted in the database, along with the id of each row. This way we can avoid making another SELECT query to the database. Pretty neat, eh?

The UPSERT clause

You can read the official docs here.

Another nice little feature is the UPSERT clause. This was added in version 3.24.0 (2018-06-04) and it causes INSERT to behave either like an UPDATE or a no-op, in case of a UNIQUE CONSTRAINT or a PRIMARY KEY CONSTRAINT violation.

To elaborate, let's suppose that you have an action_records table which holds all actions fired by users in the users table, for a specific session. When a new action is fired you want to either insert a new action_record with no error, or, if existing AND has the same session timestamp (this is handled by the ON CONFLICT clause), update the old one. You can also optionally add a WHERE statement which will result in a no-op, if not met. The query below should do it:

-- Create users table and assign userID and sessionStartTimestamp as a UNIQUE CONSTRAINT.
DROP TABLE IF EXISTS "action_records";
CREATE TABLE IF NOT EXISTS "action_records" (
    "sessionStartTimestamp" INTEGER NOT NULL,
    "errorMsg" TEXT,
    UNIQUE(userID, sessionStartTimestamp)

-- Insert new record or update the old one based on UNIQUE_CONSTRAINT OF userID & session_start_timestamp
INSERT INTO action_records (userID, errorMsg, sessionStartTimestamp) 
VALUES (258, null, 643911868) 
ON CONFLICT(userID, sessionStartTimestamp) -- Conflict when a record for the same user and session exists
DO UPDATE SET errorMsg = 'An error occured'
WHERE errorMsg IS NOT NULL -- This will be a no-op in case there is already an error and you don't want to update it
RETURNING *; -- Optionally adding RETURNING to retrieve any number of columns we want
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One thing I really liked is the fact that you can combine those clauses by simply adding RETURNING * at the end of the query. This way any row (or specified columns), either inserted or updated, will be returned.

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