How to check if a table exists in a given schema

How to Check if a Table Exists in a Given Schema 📊💡

Are you working with a PostgreSQL database and need to check if a specific table exists in a particular schema?

In this blog post, we'll address this common issue and provide you with easy solutions. By the end, you'll be able to determine if a table exists, even in cases where it exists in multiple schemas. Let's get started! 🚀💻

The Context 📝🔍

In PostgreSQL 8.4 and greater databases, common tables are typically stored in the public schema, while company-specific tables are stored in individual company schemas. The company schemas are named in the format companyX, where X represents the company number.

For example, you may have schemas such as:

• public
• company1
• company2
• company3

• ...

Each application works with a single company, and the search_path parameter in the connection string specifies the schema order to search for tables.

The Problem 🔍❓

Given this context, how can you check if a table exists in a specified companyn schema?

For instance, when using the following query:

select isSpecific('company3','tablenotincompany3schema')

The expected result is false.

And when using:

select isSpecific('company3','tableincompany3schema')

The expected result is true.

The function should only check the specified companyn schema and not other schemas. Additionally, if the given table exists in both the public schema and the specified schema, the function should return true. Finally, it should be compatible with PostgreSQL 8.4 and later versions.

Easy Solution 💡🛠️

To solve this problem, we can create a function that checks for the existence of a table in a given schema. Here's an example of how the function can be implemented:

CREATE OR REPLACE FUNCTION isSpecific(schema_name text, table_name text)
  RETURNS boolean
AS $$
BEGIN
  RETURN EXISTS (
    SELECT 1
    FROM pg_catalog.pg_tables
    WHERE schemaname = schema_name
    AND tablename = table_name
  );
END;
$$ LANGUAGE plpgsql;

How the Function Works 🔄🛠️

The isSpecific function takes two parameters: schema_name and table_name. It uses the EXISTS keyword to determine whether a table exists in the specified schema.

Here's how the function works:

1. It queries the pg_catalog.pg_tables system catalog view.

2. The schemaname column is compared with the schema_name parameter to ensure that the table is checked only in the specified schema.

3. The tablename column is compared with the table_name parameter.

4. If a row is found, the function returns true; otherwise, it returns false.

Conclusion and Call-to-Action ✅📢

You've now learned how to check if a table exists in a given schema in PostgreSQL. By using the isSpecific function we created, you can easily determine whether a table exists, even if it exists in multiple schemas.

Feel free to implement this function in your own PostgreSQL database and adjust it to fit your specific needs. If you have any questions or encounter any issues, don't hesitate to reach out for further assistance.

So go ahead, try out the isSpecific function and let us know how it works for you! 😄🎉