How to diagnose and fix the 2201W invalid_row_count_in_limit_clause error code in Postgres.

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The 2201W error code in PostgreSQL, known as invalid_row_count_in_limit_clause, indicates that the value specified in the LIMIT clause of a query is not valid. The LIMIT clause is used to restrict the number of rows returned by a query, and it expects a non-negative integer, or in some cases, an expression that evaluates to a non-negative integer.

To diagnose and fix this error, you should:

  1. Check the LIMIT Value: Ensure that the value you are using in the LIMIT clause is a non-negative integer. Negative numbers, non-numeric types, or expressions that evaluate to negative numbers will result in the 2201W error.
  2. Use a Positive Integer or Zero: The LIMIT clause should be followed by a non-negative integer or an expression that evaluates to a non-negative integer. If you want to return all rows, you can omit the LIMIT clause entirely.
  3. Avoid Non-Numeric Types: Do not use non-numeric types like strings or dates in the LIMIT clause, as they will cause this error.
  4. Check for NULL Values: Using a NULL value in the LIMIT clause will also result in an error. If you’re constructing the LIMIT dynamically, make sure to handle cases where the value might be NULL.

Examples of how to fix the 2201W error:

  • Incorrect Usage with Negative Number:
  -- Causes 2201W error
  SELECT * FROM your_table LIMIT -10;

  -- Fix: Use a non-negative integer
  SELECT * FROM your_table LIMIT 10; -- Correct
  • Incorrect Usage with Non-Numeric Type:
  -- Causes 2201W error
  SELECT * FROM your_table LIMIT 'ten';

  -- Fix: Use an integer
  SELECT * FROM your_table LIMIT 10; -- Correct
  • Handling NULL Values:
  -- Causes 2201W error if 'row_count' is NULL
  SELECT * FROM your_table LIMIT row_count;

  -- Fix: Check for NULL and use a default value or omit the LIMIT
  SELECT * FROM your_table LIMIT COALESCE(row_count, 10); -- Correct
  -- or
  SELECT * FROM your_table LIMIT ALL; -- Correct, returns all rows
  • Using Expressions:
  -- Causes 2201W error if the expression evaluates to a negative number
  SELECT * FROM your_table LIMIT (5 - 10);

  -- Fix: Ensure the expression evaluates to a non-negative integer
  SELECT * FROM your_table LIMIT GREATEST(5 - 10, 0); -- Correct, will use 0 as the LIMIT

By checking the value used in the LIMIT clause and ensuring it is a non-negative integer, you can avoid the 2201W error. If the LIMIT is being generated dynamically in your application, add appropriate checks to ensure that the value is always valid.

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