PostgreSQL raises duplicate_column when the same column name appears twice in the target list or table definition.
PostgreSQL duplicate_column (SQLSTATE 42701) occurs when a column is listed more than once in a CREATE TABLE, SELECT list, or ALTER TABLE statement. Rename or remove the repeated column to resolve the error.
duplicate_column
PostgreSQL throws duplicate_column when a statement defines or returns the same column name twice. The server halts execution because it cannot decide which duplicate to keep.
The error commonly appears during CREATE TABLE, ALTER TABLE ADD COLUMN, SELECT with column aliases, and materialized view creation. Fixing it ensures predictable column ordering and prevents silent data loss.
PostgreSQL scans every target list in a statement.
If two items resolve to the same identifier, the parser raises SQLSTATE 42701 before planning.
Typical triggers include copying column definitions, merging SELECT statements with *, or adding a column that already exists in the table.
Identify the repeated name in the failing statement. Remove it, change the alias, or qualify the column with a different label using AS.
When altering tables, check information_schema.columns before adding a new column.
In CREATE TABLE, ensure each column name is unique.
Scenario: CREATE TABLE AS SELECT * plus extra columns. Solution: list columns explicitly and rename duplicates.
Scenario: SELECT *, column AS column from table. Solution: omit the duplicate alias or give a new alias.
Always use explicit column lists instead of SELECT *.
Adopt naming conventions that prevent collision between generated and manual aliases.
In CI pipelines, run pg_dump --schema-only and lint DDL to catch duplicate names before deployment. Galaxy’s schema-aware autocomplete highlights duplicates in real time, preventing the error from reaching production.
42703 undefined_column - occurs when a referenced column does not exist. Verify spelling or schema search path.
42P07 duplicate_table - triggered by creating a table that already exists.
Drop or rename the existing table or use IF NOT EXISTS.
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The error exists in all supported PostgreSQL versions. Behavior is consistent across 9.x to 16.
No. PostgreSQL must know unique column names. You must rewrite the statement.
New columns introduced into tables can collide with manual aliases in existing queries, causing duplicate_column.
Galaxy’s editor warns when an alias duplicates an existing column and offers AI-powered refactors that automatically rename conflicts.
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