# Tables

## What is a Table?

Tables are the core unit of database [schema](/concepts/sql/schema.md). Tables are defined by a set of columns. Columns can be [primary keys](/concepts/sql/primary-key.md) which act as a unique identifier for each row. Once a table schema is defined, rows containing data can be inserted into the table.

Table data is stored on disk. The way a database lays out it's table data on disk defines some of the performance characteristics of the database.

## How to use Tables

Structure the data in your database into tables. Define relationships between tables using foreign key [constraints](/concepts/sql/constraints.md). Use `CREATE` statements to create tables and `ALTER` statements to change their schema.

## Difference between Postgres Table and Doltgres Table

A Postgres and Dolt table function the same on the surface. `CREATE` and `ALTER` statements work the same on both.

Dolt and Postgres are [row major](https://en.wikipedia.org/wiki/Row-_and_column-major_order), meaning row values are stored next to each other. However, Postgres stores data in a binary tree structure while Dolt stores table data on disk using a content-addressed binary tree called a [prolly tree](https://docs.dolthub.com/architecture/storage-engine/prolly-tree). This setup makes Dolt [fairly comparable in query performance to Postgres](/reference/benchmarks/latency.md) while also providing history-independence and fast `diff` between versions. Fast `diff` powers Dolt's version control capabilities.

## Interaction with Dolt Version Control

Dolt versions table schema and data. A table in Dolt is akin to a file in Git, it is the unit of change. Tables are the target of `select dolt_add()`.

## Example

```SQL
doltgres=> \dt
        List of relations
 Schema | Name | Type  |  Owner
--------+------+-------+----------
 public | t1   | table | postgres
(1 row)
```


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