Understanding Case Sensitivity of Column Names in PostgreSQL

• SQL (Structured Query Language): This is a general language used to interact with relational databases like PostgreSQL. It allows you to perform tasks like creating tables, inserting data, and querying information.
• PostgreSQL: This is a specific database management system that implements the SQL language. There can be variations in how different SQL implementations handle certain features, like case sensitivity of column names.
• Identifier: In SQL, this refers to a name given to something in the database, like a table name, column name, or function name.

So, are PostgreSQL column names case-sensitive?

Yes, PostgreSQL column names are case-sensitive, but with a twist. By default, PostgreSQL converts all unquoted identifiers (including column names) to lowercase internally. This means that "MyColumn" and "mycolumn" would be treated as the same column.

However, you can use double quotes to force PostgreSQL to recognize the exact name you specify, including the case. So, "MyColumn" and ""MyColumn"" would be considered different columns.

Here's an example:

-- This will select data from the column named "username" (case-insensitive)
SELECT * FROM my_table WHERE username = 'Alice';

-- This will select data from the column named exactly "UserName" (case-sensitive)
SELECT * FROM my_table WHERE "UserName" = 'Alice';

In summary:

• By default, PostgreSQL treats unquoted column names as case-insensitive (converting them to lowercase).
• You can use double quotes to make column names case-sensitive.
• It's generally recommended to use lowercase with underscores (e.g., "first_name") for consistency and readability in PostgreSQL.

CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  "Username" VARCHAR(50) NOT NULL,  -- Username in double quotes (case-sensitive)
  username VARCHAR(50) NOT NULL  -- username in lowercase (treated the same as Username)
);

INSERT INTO users (Username, username) VALUES ('Bob', 'bob');

-- This will select the row because internally both usernames become 'bob'
SELECT * FROM users WHERE username = 'bob';

-- This will also select the row for the same reason
SELECT * FROM users WHERE "Username" = 'bob';

Scenario 2: Case-sensitive (using double quotes)

CREATE TABLE products (
  product_id SERIAL PRIMARY KEY,
  "Product_Name" VARCHAR(100) NOT NULL,
  price DECIMAL(10,2) NOT NULL
);

INSERT INTO products ("Product_Name", price) VALUES ('Coffee Mug', 12.99);

-- This will select the row because "Product_Name" matches exactly
SELECT * FROM products WHERE "Product_Name" = 'Coffee Mug';

-- This will NOT select any rows because 'product_name' is different from "Product_Name"
SELECT * FROM products WHERE product_name = 'Coffee Mug';

1. Information Schema Views:

PostgreSQL provides information schema views that store details about database objects. You can use the information_schema.columns view to retrieve information about columns, including their actual names (case preserved). Here's an example:

SELECT column_name
FROM information_schema.columns
WHERE table_name = 'your_table_name';

This will return a list of column names exactly as they were created, including any case sensitivity.

1. pg_catalog.pg_ident_schemaname:

This system function allows you to get the schema name of an identifier. Since PostgreSQL stores quoted identifiers with their original case, you can check if the returned schema name matches the expected name (including case) to determine if the column name is case-sensitive. Here's an example:

SELECT pg_ident_schemaname('MyColumn');  -- Case-sensitive
SELECT pg_ident_schemaname("MyColumn"); -- Case-sensitive
SELECT pg_ident_schemaname(mycolumn);   -- Not case-sensitive (converted to lowercase)

In this example, only the quoted versions of "MyColumn" will return the expected schema name, indicating they are case-sensitive.

1. Try-Catch Block (for DDL statements):

While not ideal for existing columns, you can use a try-catch block to test if a DDL statement (like a SELECT) would succeed with the expected case for the column name. If it fails due to case mismatch, you'll know the column is case-sensitive. This approach is more suitable for checking during development or scripting.

Here are some additional points to consider:

• These methods provide indirect ways to understand case sensitivity.
• Generally, it's recommended to use consistent lowercase with underscores for column names in PostgreSQL to avoid confusion.
• If you're unsure about existing column names, consult the table definition or information schema views.