How to diagnose and fix the 25007 schema_and_data_statement_mixing_not_supported error code in Postgres.

by

The 25007 error code in PostgreSQL, schema_and_data_statement_mixing_not_supported, indicates that you are trying to execute schema and data definition statements within the same transaction while in a transaction block that has been set to READ ONLY. The PostgreSQL transaction mode READ ONLY is designed to prevent any changes to the database that would affect the data, including both data modifications and schema changes.

Here are several examples and solutions for fixing this error:

Example 1: Mixing Schema and Data Statements in READ ONLY Transaction

-- Incorrect way that causes error 25007
BEGIN TRANSACTION READ ONLY;
CREATE TABLE my_table (id SERIAL PRIMARY KEY, name TEXT);
INSERT INTO my_table (name) VALUES ('John Doe');
COMMIT;

-- Correct way
-- Separate the transactions or remove the READ ONLY restriction
BEGIN;
CREATE TABLE my_table (id SERIAL PRIMARY KEY, name TEXT);
COMMIT;

BEGIN;
INSERT INTO my_table (name) VALUES ('John Doe');
COMMIT;

Example 2: Altering a Table in READ ONLY Transaction

-- Incorrect way that causes error 25007
BEGIN TRANSACTION READ ONLY;
ALTER TABLE my_table ADD COLUMN email TEXT;
COMMIT;

-- Correct way
-- Run the ALTER TABLE statement outside of a READ ONLY transaction
BEGIN;
ALTER TABLE my_table ADD COLUMN email TEXT;
COMMIT;

Example 3: Using READ ONLY for Selective Operations

-- Incorrect way that causes error 25007
BEGIN TRANSACTION READ ONLY;
UPDATE my_table SET name = 'Jane Doe' WHERE id = 1;
COMMIT;

-- Correct way
-- Use READ ONLY transaction for SELECT statements only
BEGIN TRANSACTION READ ONLY;
SELECT * FROM my_table WHERE id = 1;
COMMIT;

-- Use a separate transaction for the UPDATE statement
BEGIN;
UPDATE my_table SET name = 'Jane Doe' WHERE id = 1;
COMMIT;

Example 4: Creating Index in READ ONLY Transaction

-- Incorrect way that causes error 25007
BEGIN TRANSACTION READ ONLY;
CREATE INDEX idx_name ON my_table (name);
COMMIT;

-- Correct way
-- Run the CREATE INDEX statement outside of a READ ONLY transaction
BEGIN;
CREATE INDEX idx_name ON my_table (name);
COMMIT;

Example 5: Using Savepoints to Partially Rollback

If you are using savepoints to partially rollback in a READ ONLY transaction, ensure that you do not include schema changes that would cause the 25007 error.

-- Incorrect way that causes error 25007
BEGIN TRANSACTION READ ONLY;
SAVEPOINT my_savepoint;
ALTER TABLE my_table ADD COLUMN phone TEXT;
ROLLBACK TO SAVEPOINT my_savepoint;
COMMIT;

-- Correct way
-- Do not include schema changes in the transaction
BEGIN TRANSACTION READ ONLY;
SAVEPOINT my_savepoint;
SELECT * FROM my_table;
-- Perform other read-only operations
ROLLBACK TO SAVEPOINT my_savepoint;
COMMIT;

To fix the 25007 error, ensure that you only perform data querying operations within a READ ONLY transaction, and handle schema changes or data modifications in a separate transaction without the READ ONLY restriction. Always check whether the transaction mode is appropriate for the operations you intend to perform.

For more details on transaction modes and restrictions in PostgreSQL, you can refer to the official PostgreSQL documentation, which provides comprehensive information on the SET TRANSACTION command and transaction isolation levels.

Leave a Comment