PostgreSQL error 42703 occurs when a query references a column that doesn't exist in the table. This is usually caused by typos, case sensitivity issues, or schema changes.
PostgreSQL error 42703 (undefined_column) indicates that your SQL query is trying to access a column that the database cannot find. This error happens at parse time, before the actual query executes, which protects your data by preventing invalid operations. The column name mismatch can occur in SELECT, INSERT, UPDATE, or DELETE statements, and is one of the most common SQL errors developers encounter when working with PostgreSQL databases.
First, check your query for typos. Review the exact spelling of the column name you're referencing:
SELECT * FROM users WHERE user_name = 'john';Compare it carefully with the actual column name in your table. Even one character difference will cause the error.
Use the information_schema to list all columns in your target table:
SELECT column_name
FROM information_schema.columns
WHERE table_name = 'users';Alternatively, use the psql command line tool:
\d usersThis will show you all columns with their exact names and types. Verify that the column you're trying to access actually exists.
If your column was created with mixed case (e.g., "UserName"), you must use double quotes to reference it:
SELECT "UserName" FROM users WHERE id = 1;Without quotes, PostgreSQL converts unquoted identifiers to lowercase, resulting in the undefined column error. This is PostgreSQL's standard behavior for identifier case handling.
When using multiple tables, always prefix column names with the appropriate table alias:
SELECT u.id, u.name, p.title
FROM users u
JOIN posts p ON u.id = p.user_id
WHERE u.id = 1;Without the table prefix (u., p.), PostgreSQL cannot determine which table the column belongs to, causing the undefined_column error.
If the column truly doesn't exist and you need to add it, use ALTER TABLE:
ALTER TABLE users ADD COLUMN email VARCHAR(255);After adding the column, update your queries to reference it correctly. For optional columns that may not have values yet, consider adding a DEFAULT value or making the column nullable.
PostgreSQL is case-sensitive for quoted identifiers but case-insensitive for unquoted ones. When a column is created with quotes (e.g., CREATE TABLE users (id INT, "UserName" VARCHAR)), it preserves the exact case. Referencing it later without quotes converts the identifier to lowercase, causing a mismatch. Additionally, schema search path issues can cause similar errors if multiple schemas contain tables with the same name but different columns. Check your current schema search path with "SHOW search_path;" and ensure you're querying the correct schema. For CTEs (WITH clauses), ensure column references match the CTE column names exactly. This error also occurs in views, functions, triggers, and prepared statements when their body contains unresolved column references.
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