Why Am I Getting an \'Undeclared Variable\' Error When Using SELECT INTO?

Undeclared Variable Error When Using SELECT INTO Query

When attempting to execute a SELECT INTO statement that stores the results into a variable, you may encounter the following error:

Undeclared variable:

This error typically occurs when the variable specified in the INTO clause has not been declared or initialized beforehand.

Example

Consider the following query:

SELECT id_subscriber
  INTO newsletter_to_send
  FROM subscribers 

When you attempt to execute this query, you will receive the error message "#1327 - Undeclared variable: newsletter_to_send". This error indicates that the variable "newsletter_to_send" has not been created or assigned a value.

Solution

To resolve this error, you must utilize the INSERT...SELECT statement instead:

INSERT INTO newsletter_to_send
SELECT id_subscriber FROM subscribers 

The INSERT...SELECT statement allows you to insert the results of a query directly into a specified table, effectively creating the target variable in the process.

Additional Note

It is important to ensure that the query used in the INSERT...SELECT statement is correct and does not produce duplicate records. Consider adding a WHERE clause to filter the data as necessary.

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