How to fix Array subscript error in PostgreSQL

PostgreSQLINTERMEDIATEMEDIUMUpdated Dec 26, 2025· 191 views

PostgreSQL raises an array subscript error when accessing an array element with an invalid or out-of-bounds index. This commonly occurs when using multi-dimensional arrays or when index values exceed the array bounds, especially in PL/pgSQL functions.

Quick fix

Fixes Array subscript error

-- WRONG: Accessing index 0
SELECT my_array[0];

-- CORRECT: Access index 1 for the first element
SELECT my_array[1];
  1. Check array indexing convention
  2. Verify array bounds before accessing elements
  3. Use array_upper and array_lower for bounds
  4. Initialize multi-dimensional arrays properly
postgresql — error
-- WRONG: Accessing index 0
SELECT my_array[0];
-- CORRECT: Access index 1 for the first element
SELECT my_array[1];
Array subscript error

What this error means

PostgreSQL arrays are 1-based by default, meaning the first element is at index 1, not 0. When you attempt to assign a value to an array element at an index outside the existing bounds, or access an index that does not exist, PostgreSQL raises an error. This is particularly important with multi-dimensional arrays, which cannot be dynamically resized like one-dimensional arrays.

Typical symptoms

  • Error message "array subscript out of range" during INSERT, UPDATE, or query execution
  • PL/pgSQL functions fail when trying to assign values to array indices
  • Multi-dimensional array operations throw subscript errors
  • Queries fail when attempting to access array elements beyond the declared bounds

Common causes

  1. Attempting to access array index 0 instead of 1 (PostgreSQL uses 1-based indexing)
  2. Using an index larger than the array size without first expanding the array
  3. In multi-dimensional arrays, trying to assign to elements that do not fit within existing dimensions
  4. Forgetting that multi-dimensional arrays cannot be dynamically resized by assigning to arbitrary positions
  5. Not checking array bounds before accessing elements in PL/pgSQL code

How to fix "Array subscript error"

1Check array indexing convention

Remember that PostgreSQL arrays are 1-based by default, not 0-based like many programming languages.

sql
-- WRONG: Accessing index 0
SELECT my_array[0];

-- CORRECT: Access index 1 for the first element
SELECT my_array[1];
2Verify array bounds before accessing elements

Use the array_length() function to get the size of an array dimension, and validate indices before access:

sql
-- Check the length of the first dimension
SELECT array_length(my_array, 1) AS array_size;

-- Safe access with bounds checking
SELECT 
  CASE 
    WHEN idx BETWEEN 1 AND array_length(my_array, 1) 
    THEN my_array[idx]
    ELSE NULL 
  END AS safe_value
FROM table_name;
3Use array_upper and array_lower for bounds

For more explicit control, use array_upper() and array_lower() to get the actual upper and lower bounds:

sql
SELECT 
  array_lower(my_array, 1) AS lower_bound,
  array_upper(my_array, 1) AS upper_bound;

-- Safe loop in PL/pgSQL
FOR i IN array_lower(my_array, 1) .. array_upper(my_array, 1) LOOP
  RAISE NOTICE 'Element: %', my_array[i];
END LOOP;
4Initialize multi-dimensional arrays properly

For multi-dimensional arrays, use array_fill() to create properly sized arrays before assignment:

sql
-- Create a 3x2 array filled with NULL
DECLARE
  my_array INT[][];
BEGIN
  my_array := array_fill(NULL::INT, ARRAY[3, 2]);
  -- Now safe to assign to any position within [1:3][1:2]
  my_array[2][1] := 42;
END;
5Handle out-of-bounds gracefully in PL/pgSQL

Add explicit bounds checking in PL/pgSQL to prevent errors:

sql
CREATE FUNCTION safe_array_access(arr INT[], idx INT) RETURNS INT AS $$
BEGIN
  IF idx < array_lower(arr, 1) OR idx > array_upper(arr, 1) THEN
    RETURN NULL;
  END IF;
  RETURN arr[idx];
END;
$$ LANGUAGE plpgsql IMMUTABLE;

Advanced notes

PostgreSQL differs from many languages in its 1-based array indexing and its handling of out-of-bounds reads (which return NULL rather than error). When assigning to arrays, you can expand 1-dimensional arrays by assigning to an index beyond the current size, filling intermediate positions with NULL. However, multi-dimensional arrays have stricter rules—you cannot dynamically resize them by assigning to arbitrary indices. Always initialize multi-dimensional arrays with array_fill() or literal syntax to define all dimensions upfront. In historical PostgreSQL versions, there were security fixes related to integer overflow in array subscript calculations, so ensure you are running a patched version if working with very large arrays.

Frequently asked questions

What does "Array subscript error" mean?
PostgreSQL arrays are 1-based by default, meaning the first element is at index 1, not 0. When you attempt to assign a value to an array element at an index outside the existing bounds, or access an index that does not exist, PostgreSQL raises an error. This is particularly important with multi-dimensional arrays, which cannot be dynamically resized like one-dimensional arrays.
How do I fix "Array subscript error"?
PostgreSQL raises an array subscript error when accessing an array element with an invalid or out-of-bounds index. This commonly occurs when using multi-dimensional arrays or when index values exceed the array bounds, especially in PL/pgSQL functions.
What causes "Array subscript error"?
Attempting to access array index 0 instead of 1 (PostgreSQL uses 1-based indexing) Using an index larger than the array size without first expanding the array In multi-dimensional arrays, trying to assign to elements that do not fit within existing dimensions
Is the "Array subscript error" error serious?
It is a medium-severity error — more of a blocker than a risk. The steps above resolve it.

Official resources & further reading