How to diagnose and fix the 2202E array_subscript_error error code in Postgres.

The 2202E error code in PostgreSQL, typically shown as “ERROR: array subscript out of range,” occurs when you try to access or assign a value to an array element with an index that is outside the bounds of the array.

Here are some steps to diagnose and fix this error:

  1. Check Array Bounds: Ensure that the array index you are accessing is within the range of the array’s defined bounds. PostgreSQL arrays are 1-based by default, meaning the first element is at index 1, not 0.
  2. Initializing Arrays: If you’re working with multi-dimensional arrays, make sure that each dimension of the array is properly initialized. Unlike 1D arrays, multi-dimensional arrays cannot be dynamically resized by simply assigning to elements not already present. As per a Stack Overflow discussion, you cannot grow a multi-dimensional array like you can with 1D arrays.
  3. Array Assignment: When assigning to an array, ensure that you’re not implying a dynamic resizing of the array, which is not supported in PL/pgSQL. For example, a[i][j]:=i*j; would throw an error if a is not already a sufficiently large multi-dimensional array.
  4. Using array_fill(): If you need to create a multi-dimensional array with a specific size, you can use the array_fill() function to create a “blank canvas” array with all cells set to the same specified value. This can help prevent subscript out of range errors by ensuring that all required indices are initialized (YugabyteDB Docs).
  5. Avoiding Gaps: When working with arrays, especially in PL/pgSQL, avoid operations that create gaps. For example, assigning a value to an array at a position that does not follow the immediate next index can lead to errors.

Here are some examples of how to avoid the 2202E error:

  • Correct Array Initialization:
  SELECT array_fill(0, ARRAY[3, 3]);

This will create a 3×3 multi-dimensional array filled with zeros.

  • Proper Index Access:
  -- Assuming my_array is a one-dimensional array with at least 3 elements
  SELECT my_array[3];

This will select the third element of my_array.

  • Safe Array Assignment:
  -- Assuming my_array is a one-dimensional array with at least 3 elements
  DO $$
    my_array integer[] := '{1,2,3}';
    my_array[3] := 4;
  END $$;

This will safely assign the value 4 to the third element of my_array.

By following these guidelines and examples, you should be able to diagnose and fix the 2202E array subscript error in PostgreSQL. Remember to always check that your array indices are within bounds and that multi-dimensional arrays are properly initialized before use.

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