Postgresql "Column does not exist" but it actually does

Case sensitivity: nasty beast or helpful creature?

PostgreSQL identifiers, such as column names, are case-insensitive by default. However, the scene changes dramatically when double quotes enter the picture:

-- These are besties:
SELECT column_name FROM my_table;
SELECT COLUMN_NAME FROM my_table;
SELECT Column_Name FROM my_table;

-- These guys barely talk:
SELECT "column_name" FROM my_table; --"Hi, nice to meet you!"
SELECT "COLUMN_NAME" FROM my_table; --"Who are you again?"


Try using lowercase for column names to avoid case sensitivity. Unquoted names are stored in lowercase by default.

Special characters and whitespaces: wanted or not?

White spaces or special characters in column names require double quotes:

CREATE TABLE my_table (
    "A Column" text,
    "Another-Column" integer
);

SELECT "A Column", "Another-Column" FROM my_table;


Hidden characters or whitespaces? Those sneaky troublemakers could be in your column names! Paste the name from your DB schema to catch them red-handed.

What table are we eating at?

Confirm you're dining at the right table and serving from the correct schema:

--Waiter! I'd like to order "column_name" from "schema_name"."table_name". Table for one, please.
SELECT "column_name" FROM "schema_name"."table_name";


Mismatched application model and database structure can leave a sour taste in your mouth. Keep your schema migrations fresh from the kitchen!

SQL syntax: secret spice or bitter herb?

From column names to SQL syntax and operators:

• Single quotes for string literals—no doubles! Cheating on doubles with singles, staying string to our rule.
• Comparison operators must match the column data type. "Apples to apples, oranges to oranges."

Testing and Troubleshooting: keep or fold?

Always bet on testing your query directly in the PostgreSQL console or psql tool. Java application? Turn on the log-light to see what's being dished out to the DB:

--"Waiter! There's a typo in my soup."
LOG: SELECT "yourClumn" FROM your_table;


Quoting the unquoteables

Reserved words for column names? It's fraught with peril! Always keep them safe in quotes:

-- Yes, we have "user" on the menu. And yes, it comes quoted.
SELECT "user" FROM my_table;


Changing column names? Here's how you give your column a new identity:

-- Goodbye, Old Column. Welcome, new_column! New name, fresh start.
ALTER TABLE my_table RENAME COLUMN "Old Column" TO new_column;


Step-by-step elimination

Diagnosing the problem

Before making drastic changes, complete a thorough diagnosis:

• Run \d table_name in psql to reveal the truth.
• Toggle \x command for clarity's sake.
• Cross-verify column data types—incorrect types can wreak similar havoc in join or comparison queries.

Digging Deeper with PostgreSQL Functions

Meet the functions at your disposal:

SELECT * FROM pg_catalog.pg_attribute WHERE attrelid = 'my_table'::regclass;


This query lists the actual columns of my_table stored in the system catalog.

Controlled migrations

For renaming or changing schema:

• Have orderly migration scripts with definite up and down paths.
• After running migrations, schema diff tool will confirm the changes.
• Tools like Alembic or Flyway can ensure error-free schema migrations.

A developer's golden rules

Follow these simple rules:

• Keep sync between application and database schema.
• Stick to naming conventions: lowercase with underscores is friendly for PostgreSQL.
• Avoid altering the schema manually and breaking migration scripts' trust.