Why does my query \'SELECT INTO\' result in an \'Undeclared Variable\' error?

SELECT INTO and Error: Undeclared Variable

When attempting to execute the query:

SELECT id_subscriber
INTO newsletter_to_send
FROM subscribers

You encounter an error:

#1327 - Undeclared variable: newsletter_to_send

Cause:

The error arises because the variable newsletter_to_send is not declared or initialized before its use in the query.

Solution:

To resolve this issue, you need to use the INSERT ... SELECT syntax instead of the SELECT INTO syntax. The correct query should be:

INSERT INTO newsletter_to_send
SELECT id_subscriber
FROM subscribers

The INSERT ... SELECT syntax allows you to insert multiple rows into a table by using the results of a subquery.

Additional Note:

It's worth considering if there is a need for a WHERE clause in the subquery to filter the results and potentially prevent inserting unwanted rows into the newsletter_to_send table.

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