Common issues

Here are some common errors and issues with the Postgres node and steps to resolve or troubleshoot them.

Dynamically populate SQL IN groups with parameters

In Postgres, you can use the SQL IN comparison construct to make comparisons between groups of values:

SELECT color, shirt_size FROM shirts WHERE shirt_size IN ('small', 'medium', 'large');

While you can use n8n expressions in your query to dynamically populate the values in an IN group, combining this with query parameters provides extra protection by automatically sanitizing input.

To construct an IN group query with query parameters:

1. Set the Operation to Execute Query.

2. In Options, select Query Parameters.

3. Use an expression to select an array from the input data. For example, {{ $json.input_shirt_sizes }}.

4. In the Query parameter, write your query with the IN construct with an empty set of parentheses. For example:

   SELECT color, shirt_size FROM shirts WHERE shirt_size IN ();

5. Inside of the IN parentheses, use an expression to dynamically create index-based placeholders (like $1, $2, and $3) for the number of items in your query parameter array. You can do this by increasing each array index by one since the placeholder variables are 1 indexed:

   SELECT color, shirt_size FROM shirts WHERE shirt_size IN ({{ $json.input_shirt_sizes.map((i, pos) => "$" + (pos+1)).join(', ') }});

With this technique, n8n automatically creates the correct number of prepared statement placeholders for the IN values according to the number of items in your array.

Working with timestamps and time zones

To avoid complications with how n8n and Postgres interpret timestamp and time zone data, follow these general tips:

• Use UTC when storing and passing dates: Using UTC helps avoid confusion over timezone conversions when converting dates between different representations and systems.

• Set the execution timezone: Set the global timezone in n8n using either environment variables (for self-hosted) or in the settings (for n8n Cloud). You can set a workflow-specific timezone in the workflow settings.

• Use ISO 8601 format: The ISO 8601 format encodes the day of the month, month, year, hour, minutes, and seconds in a standardized string. n8n passes dates between nodes as strings and uses Luxon to parse dates. If you need to cast to ISO 8601 explicitly, you can use the Date & Time node and a custom format set to the string yyyy-MM-dd'T'HH:mm:ss.

Outputting Date columns as date strings instead of ISO datetime strings

n8n's uses the pg package to integrate with Postgres, which affects how n8n processes date, timestamp, and related types from Postgres.

The pg package parses DATE values into new Date(row_value) by default, which produces a date that follows the ISO 8601 datetime string format. For example, a date of 2025-12-25 might produce a datetime sting of 2025-12-25T23:00:00.000Z depending on the instance's timezone settings.

To work around this, use the Postgres TO_CHAR function to format the date into the expected format at query time:

SELECT TO_CHAR(date_col, 'YYYY-MM-DD') AS date_col_as_date FROM table_with_date_col

This will produce the date as a string without the time or timezone components. To continue the earlier example, with this casting, a date of 2025-12-25 would produce the string 2025-12-25. You can find out more in the pg package documentation on dates.