38002ERRORTier 2 — Caution✅ HIGH confidence

modifying SQL data not permitted

Category: External Routine ExceptionVersions: All Postgres versions

What this means

SQLSTATE 38002 is raised when an external routine declared as READS SQL DATA or CONTAINS SQL (read-only) attempts to execute a data-modifying statement.

Why it happens

1An external function declared with a read-only data access attribute executes INSERT, UPDATE, DELETE, or other data-modifying SQL

How to reproduce

Read-only external function attempting a write.

trigger — this will ERROR

ERROR: modifying SQL-data not permitted

Fix 1: Declare the external function as MODIFIES SQL DATA if it writes data

When the function needs to modify data.

fix

CREATE FUNCTION my_c_func() RETURNS VOID
AS 'my_extension', 'my_c_func'
LANGUAGE C
MODIFIES SQL DATA;

Why this works

The MODIFIES SQL DATA attribute permits the function to execute write operations.

Sources

📚 Official docs: https://www.postgresql.org/docs/current/errcodes-appendix.html

🔧 Source ref: Class 38 — External Routine Exception

Confidence assessment

✅ HIGH confidence

Standard SQLSTATE. Stable across versions.