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Description

This error occurs within MySQL stored procedures when using cursors, specifically during the execution of a `FETCH` statement. It indicates that the number of target variables provided in the `INTO` clause does not match the number of columns being retrieved by the cursor's `SELECT` statement. This prevents the stored procedure from correctly processing fetched data.

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Error Message

Incorrect number of FETCH variables

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Known Causes

3 known causes

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Cursor Column Count Mismatch

The `SELECT` statement used in the `DECLARE CURSOR` defines a different number of columns than the variables listed in the `FETCH ... INTO` statement.

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Incorrect Variable Declaration

One or more variables in the `FETCH ... INTO` clause are either not declared, misspelled, or have an incorrect scope, leading MySQL to miscount the expected variables.

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Underlying Table Structure Changes

The schema of the table(s) from which the cursor selects data has changed (e.g., columns added or removed) since the stored procedure was last defined or reviewed, making the cursor's definition outdated.

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Solutions

3 solutions available

1. Verify SELECT List and FETCH Variables Count easy

Ensure the number of columns in your SELECT statement exactly matches the number of variables in your FETCH statement.

1

Examine the `SELECT` statement within your stored procedure or script. Count the number of columns being selected.

2

Locate the `FETCH` statement. Count the number of variables it's attempting to assign the selected column values to.

FETCH cursor_name INTO var1, var2, ..., varN;

3

Adjust either the `SELECT` list or the `FETCH` variable list so that the counts are identical. If you are selecting 5 columns, you must have 5 variables in the `FETCH` statement.

-- Example of a mismatch:
-- SELECT col1, col2 FROM my_table;
-- FETCH my_cursor INTO var1;

-- Corrected example:
-- SELECT col1, col2 FROM my_table;
-- FETCH my_cursor INTO var1, var2;

2. Correct Data Type Compatibility in FETCH medium

Ensure the data types of the SELECT list columns are compatible with the declared data types of the FETCH variables.

1

Identify the data types of each column in your `SELECT` statement.

DESCRIBE your_table; -- or SHOW COLUMNS FROM your_table;

2

Review the `DECLARE` statements for the variables used in your `FETCH` statement. Note their declared data types.

DECLARE var1 INT;
DECLARE var2 VARCHAR(255);

3

Ensure that the data type of each selected column can be safely assigned to its corresponding `FETCH` variable. For instance, a `VARCHAR` can usually be assigned to another `VARCHAR` or a `TEXT` type, but assigning a large `VARCHAR` to a small `VARCHAR` might lead to truncation or other issues, though not directly error 1328. For 1328, the primary concern is the *number* of items, but type mismatches *can* sometimes manifest in unexpected ways or be associated with the same code block.

-- If SELECT is VARCHAR(50) and FETCH variable is INT, this is a problem.
-- MySQL might try to coerce, but explicit compatibility is best.

-- Best practice: Match types or use compatible ones.
-- DECLARE var1 VARCHAR(50);

4

If there are type mismatches, adjust the `DECLARE` statements for your `FETCH` variables to be compatible with the selected column types.

-- Example: If SELECT returns a DATE, FETCH variable should be DATE or DATETIME.
-- DECLARE fetch_date DATE;

3. Review Cursor Definition and Usage medium

Thoroughly check the cursor's `DECLARE CURSOR` statement and how it's being used within the procedure.

1

Locate the `DECLARE CURSOR` statement. This statement defines the `SELECT` query that the cursor will iterate over.

DECLARE cursor_name CURSOR FOR SELECT column1, column2 FROM ...;

2

Carefully compare the number of columns specified in the `DECLARE CURSOR`'s `SELECT` statement with the number of variables used in the `FETCH` statement associated with this cursor.

-- Example:
-- DECLARE my_cursor CURSOR FOR SELECT id, name;
-- FETCH my_cursor INTO v_id;

3

Ensure that every column in the `DECLARE CURSOR`'s `SELECT` list has a corresponding variable in the `FETCH` statement, and vice-versa.

-- Corrected example:
-- DECLARE my_cursor CURSOR FOR SELECT id, name;
-- FETCH my_cursor INTO v_id, v_name;

4

If your stored procedure uses multiple cursors, ensure you are associating the correct `FETCH` statement with the correct cursor.

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Related Errors

5 related errors

MySQL Error 1328: Mismatched FETCH Variables