How to fix 42P14: invalid_prepared_statement_definition in PostgreSQL

Examine your PREPARE statement for SQL syntax errors. The statement must be valid SQL that can execute independently.

Example of correct PREPARE syntax:

PREPARE get_user (integer, text) AS
SELECT id, name, email FROM users
WHERE id = $1 AND status = $2;

Check for common syntax issues:
- Missing or misplaced keywords (SELECT, WHERE, FROM)
- Unmatched parentheses or quotes
- Invalid column or table names
- Missing commas in column lists

Ensure the number of parameters declared in PREPARE matches the number of placeholders ($1, $2, etc.) used in the statement.

Correct example:

-- Declares 2 parameters
PREPARE find_items (integer, text) AS
SELECT * FROM items
WHERE category_id = $1 AND name LIKE $2;

-- Execute with exactly 2 arguments
EXECUTE find_items(5, 'widget%');

Common mistakes:
- Missing parameter: PREPARE stmt (integer, text) AS SELECT * WHERE id = $1; (declares 2, uses 1)
- Extra parameter: PREPARE stmt (integer) AS SELECT * WHERE id = $1 AND name = $2; (declares 1, uses 2)
- Skipped placeholder: PREPARE stmt (int, int) AS SELECT * WHERE id = $1 AND date > $3; (uses $3 but declares 2)

Ensure parameter types are valid PostgreSQL types and consistent with how they're used in the statement.

-- Valid type examples
PREPARE stmt1 (integer, text, boolean) AS SELECT ...;
PREPARE stmt2 (numeric, timestamp) AS SELECT ...;
PREPARE stmt3 (integer[], jsonb) AS SELECT ...;

-- Invalid types that cause 42P14
PREPARE stmt4 (int64) AS SELECT ...;  -- Use "bigint" not "int64"
PREPARE stmt5 (varchar(50)) AS SELECT ...;  -- Use "varchar" or "text", not "varchar(50)" in PREPARE

Type-related issues:
- Using non-existent type names
- Mixing type name variations (int vs integer)
- Specifying length constraints on text types in parameter declarations

Verify that all tables and columns referenced in the prepared statement actually exist in the database.

-- First, verify the table structure
\d users
\d items

-- Then create the prepared statement
PREPARE get_user (integer) AS
SELECT id, name, email FROM users WHERE user_id = $1;

-- Query to check if references exist
SELECT table_name, column_name
FROM information_schema.columns
WHERE table_name = 'users';

Common reference errors:
- Typos in table names: FROM users_table when table is users
- Typos in column names: WHERE userID = $1 when column is user_id
- Using unqualified names without proper schema specification

Create and execute the same SQL as a regular statement (not prepared) to isolate syntax issues.

-- Test the SQL directly with literal values
SELECT id, name FROM users WHERE id = 123 AND status = 'active';

-- If this works, try the prepared statement with the same structure
PREPARE find_user (integer, text) AS
SELECT id, name FROM users WHERE id = $1 AND status = $2;

-- Then execute
EXECUTE find_user(123, 'active');

This approach helps identify whether the issue is with SQL syntax or parameter handling. If the direct query fails, fix the SQL before preparing it.

If you've modified a prepared statement definition, deallocate the old one first to avoid conflicts.

-- Remove the old prepared statement
DEALLOCATE prepared_statement_name;

-- Or deallocate all prepared statements in the session
DEALLOCATE ALL;

-- Create the corrected version
PREPARE prepared_statement_name (integer, text) AS
SELECT * FROM users WHERE id = $1 AND name = $2;

Important notes:
- Prepared statements are session-specific and automatically removed when the session ends
- Multiple PREPARE commands with the same name without DEALLOCATE will fail
- Some connection poolers (PgBouncer, pgpool) may need special configuration to preserve prepared statements

Ensure column or table names that are PostgreSQL reserved keywords are properly quoted.

-- Invalid: 'order' is a reserved keyword
PREPARE get_order (integer) AS
SELECT order, customer FROM orders WHERE id = $1;

-- Valid: quote the keyword
PREPARE get_order (integer) AS
SELECT "order", customer FROM orders WHERE id = $1;

-- Or use a full identifier path
PREPARE get_order (integer) AS
SELECT orders."order", orders.customer FROM orders WHERE id = $1;

Keywords to watch for: SELECT, WHERE, FROM, ORDER, GROUP, HAVING, LIMIT, etc.