How to diagnose and fix the 22026 string_data_length_mismatch error code in Postgres.

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The 22026 error code in PostgreSQL, which stands for string_data_length_mismatch, occurs when the length of a string does not match the length constraints specified for a column. For example, this can happen when you try to insert or update a string in a column that has a fixed character type (CHAR(n)) with a length different than the column’s specified size.

To diagnose and fix the 22026 error, here are the steps you should follow:

  1. Check Column Definitions: Look at the table’s column definitions to determine the exact length constraints for the CHAR(n) or other fixed-length string columns.
  2. Adjust String Length: Before inserting or updating data, make sure the length of the string matches the column’s fixed size. If the string is too long, it will need to be truncated; if it’s too short, you may need to pad it with spaces (for CHAR(n) fields).

Here’s an example of a situation that would cause a string_data_length_mismatch error:

-- Assuming there's a table with a column defined as CHAR(5)
CREATE TABLE example (
    fixed_string CHAR(5)
);

-- Trying to insert a string that's too long
INSERT INTO example (fixed_string) VALUES ('toolong');

This would cause an error because ‘toolong’ is 7 characters long, but the fixed_string column only accepts strings of exactly 5 characters.

To fix the error in this case, you would need to ensure the string is exactly 5 characters long:

-- Correctly inserting a string of length 5
INSERT INTO example (fixed_string) VALUES ('12345');

-- If the string is too short, it will be space-padded automatically by PostgreSQL
INSERT INTO example (fixed_string) VALUES ('abc');
-- The value 'abc' will be stored as 'abc  ' (with two trailing spaces)

If you have a string that’s too long and you want to forcibly truncate it to fit into the column, you could use a function like LEFT() to limit the length of the string:

-- Inserting a truncated string
INSERT INTO example (fixed_string) VALUES (LEFT('toolong', 5));

This would insert the value ‘toolo’ into the fixed_string column.

In summary, when you encounter the 22026 error code, you should verify the string lengths against the column definitions and adjust the data accordingly before attempting to insert or update the table.

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