# Source: https://docs.oxla.com/system-catalogs/catalogs/pg_class.md

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# pg_class

## Overview

The `pg_class` stores information about tables and indexes in the database. It contains exactly one row per table (or index) created in the database. It mimics the [pg\_class](https://www.postgresql.org/docs/15/catalog-pg-class.html) PostgreSQL system catalog.

## Columns

<Note>This table is designed for compatibility with tools that require PostgreSQL system tables, so it mostly has dummy data. Please note that not all columns in `pg_class` are applicable to every type of relation.</Note>

The following columns are available for querying in `pg_class`:

| Column                | Type    | Description                                                                          |
| --------------------- | ------- | ------------------------------------------------------------------------------------ |
| `oid`                 | `int`   | This column represents the table/index object ID (OID) generated by oxla             |
| `relname`             | `text`  | This column represents the table/index name as specified by the user during creation |
| `relnamespace`        | `int`   | This column represents the OID of the namespace the relation resides in              |
| `relhasindex`         | `bool`  | Returns `true` if the table has any indexes                                          |
| `relkind`             | `text`  | This column represents the type of relation: `r` for tables and `i` for indexes      |
| `reltype`             | `int`   | *Unused*                                                                             |
| `reloftype`           | `int`   | *Unused*                                                                             |
| `relowner`            | `int`   | *Unused*                                                                             |
| `relam`               | `int`   | *Unused*                                                                             |
| `relfilenode`         | `int`   | *Unused*                                                                             |
| `reltablespace`       | `int`   | *Unused*                                                                             |
| `relpages`            | `int`   | *Unused*                                                                             |
| `reltuples`           | `float` | *Unused*                                                                             |
| `relallvisible`       | `int`   | *Unused*                                                                             |
| `reltoastrelid`       | `int`   | *Unused*                                                                             |
| `relisshared`         | `bool`  | *Unused*                                                                             |
| `relpersistence`      | `text`  | *Unused*                                                                             |
| `relnatts`            | `int`   | *Unused*                                                                             |
| `relchecks`           | `int`   | *Unused*                                                                             |
| `relhasrules`         | `bool`  | *Unused*                                                                             |
| `relhastriggers`      | `bool`  | *Unused*                                                                             |
| `relhassubclass`      | `bool`  | *Unused*                                                                             |
| `relrowsecurity`      | `bool`  | *Unused*                                                                             |
| `relforcerowsecurity` | `bool`  | *Unused*                                                                             |
| `relispopulated`      | `bool`  | *Unused*                                                                             |
| `relreplident`        | `text`  | *Unused*                                                                             |
| `relispartition`      | `bool`  | *Unused*                                                                             |
| `relrewrite`          | `int`   | *Unused*                                                                             |
| `relfrozenxid`        | `int`   | *Unused*                                                                             |
| `relacl`              | `text`  | *Unused*                                                                             |
| `reloptions`          | `text`  | *Unused*                                                                             |
| `relminmxid`          | `text`  | *Unused*                                                                             |
| `relpartbound`        | `text`  | *Unused*                                                                             |

## Example

1. Create a table and define its schema:

```sql  theme={null}
CREATE TABLE customer_orders (
    order_id INT,
    customer_id INT,
    order_date DATE,
    total_amount INT
);
```

2. Create an index on the `customer_orders` table for the `customer_id` column:

```sql  theme={null}
CREATE INDEX idx_customer_id ON customer_orders (customer_id);
```

3. Query the `pg_class` catalog to retrieve information about the `customer_orders` table and the index you’ve just created:

```sql  theme={null}
SELECT oid, relname, relkind, relhasindex, relnamespace 
FROM pg_class 
WHERE relname IN ('customer_orders', 'idx_customer_id');
```

4. The query will return information about the `customer_orders` table and the index:

```sql  theme={null}
 oid  |     relname     | relkind | relhasindex | relnamespace 
------+-----------------+---------+-------------+--------------
 1013 | idx_customer_id | i       | f           |            0
 1012 | customer_orders | r       | t           |            0
(2 rows)
```