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Description

This error occurs in MySQL stored programs (procedures, functions, triggers) when a local variable is referenced in an expression or statement before it has been explicitly assigned a value. It indicates an attempt to use a variable whose content is undefined, leading to predictable runtime errors.

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Error Message

Referring to uninitialized variable %s

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Known Causes

3 known causes

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Variable Declared But Not Initialized

A variable is declared using `DECLARE` but is immediately used in an expression or statement without an initial `SET` assignment or `SELECT ... INTO` operation.

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Conditional Initialization Skipped

A variable's initialization occurs within a conditional block (e.g., `IF` statement) that is not executed, leaving the variable unassigned when later referenced.

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Typo or Scope Mismatch

A variable name is misspelled, causing a reference to a non-existent or different uninitialized variable, or the variable is used outside its defined scope.

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Solutions

4 solutions available

1. Initialize Variables Before Use easy

Explicitly set a value for any variable before referencing it.

1

Identify the variable mentioned in the error message (e.g., `@my_variable`).

2

Before the first time you use this variable in a `SELECT`, `SET`, or other statement, assign it an initial value. This can be `NULL`, `0`, an empty string, or a default value relevant to your logic.

SET @my_variable = NULL; -- or SET @my_variable = 0; or SET @my_variable = '';

3

Ensure all subsequent references to `@my_variable` occur *after* this initialization.

SELECT @my_variable;

2. Review Stored Procedures and Functions medium

Check for uninitialized local variables within stored routines.

1

Examine the source code of any stored procedures or functions that are being executed when the error occurs.

2

Locate `DECLARE` statements for local variables within the routine.

DECLARE my_local_var INT;

3

Ensure each declared local variable is assigned an initial value using `SET` or during declaration if supported by the MySQL version.

DECLARE my_local_var INT DEFAULT 0; -- Preferred for clarity
-- OR
DECLARE my_local_var INT;
SET my_local_var = 0;

4

Carefully trace the logic to ensure that any variable used in a conditional statement or calculation has been assigned a value in all possible execution paths.

3. Isolate the Problematic Query/Routine medium

Pinpoint the exact statement or block causing the error for targeted correction.

1

If the error occurs within a larger script or application, comment out sections of code incrementally to narrow down the source.

2

Once the specific `SELECT`, `UPDATE`, `DELETE`, `INSERT`, or stored procedure call is identified, reproduce it in a MySQL client (like `mysql` command-line client or MySQL Workbench).

3

Apply the initialization techniques from Solution 1 or 2 to the identified problematic statement or routine.

4. Check for Implicit Variable Creation in Older MySQL Versions advanced

Be aware that older MySQL versions might not strictly enforce variable initialization.

1

Understand that in very old versions of MySQL (pre-5.0), variables could sometimes be used without explicit initialization, leading to unpredictable behavior. This error often indicates a move towards stricter behavior or a specific edge case.

2

If you are working with an older MySQL version or migrating from one, review queries that might have relied on implicit variable behavior. Explicitly declare and initialize all session variables (`@variable_name`) and local variables within routines.

3

Consider upgrading your MySQL server if it's significantly outdated, as newer versions offer better error handling and more predictable behavior.

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Related Errors

5 related errors

MySQL Error 1311: Uninitialized Variable Reference