postgresql show tables with code examples

PostgreSQL is a powerful and open-source relational database management system. One of the common tasks when working with a database is to view the tables that are present in the database. In this article, we will look at how to show tables in PostgreSQL using various code examples.

The most basic way to show tables in PostgreSQL is to use the \dt command. This command is used to list the tables that are present in the current database. To use the \dt command, first, connect to the database using the psql command-line interface. Once connected, type \dt and press enter. This will display a list of tables in the current database.

$ psql
psql (12.5)
Type "help" for help.

postgres=# \dt
              List of relations
 Schema |   Name   | Type  |  Owner  
--------+----------+-------+---------
 public | employees | table | postgres
 public | orders    | table | postgres
(2 rows)

You can also show the tables in a specific schema by adding the schema name after the \dt command. For example, to show the tables in the 'public' schema, you can use the command \dt public.

postgres=# \dt public
              List of relations
 Schema |   Name   | Type  |  Owner  
--------+----------+-------+---------
 public | employees | table | postgres
 public | orders    | table | postgres
(2 rows)

Another way to show tables in PostgreSQL is to use the SELECT statement. The information_schema.tables view can be used to retrieve a list of tables in the current database. The following query can be used to show the tables in the current database:

SELECT table_name FROM information_schema.tables WHERE table_schema = 'public';

This query will return the list of table names in the 'public' schema. You can also use the 'WHERE' clause to filter the results based on the table name or table type.

SELECT table_name FROM information_schema.tables WHERE table_schema = 'public' AND table_name LIKE 'employ%';

This query will return the list of table names in the 'public' schema which starts with the word 'employ'.

In addition to the above methods, you can also use the pg_catalog.pg_tables view to show the tables in PostgreSQL. The pg_catalog.pg_tables view contains information about all tables in the current database. The following query can be used to show the tables in the current database:

SELECT tablename FROM pg_catalog.pg_tables WHERE schemaname = 'public';

This query will return the list of table names in the 'public' schema.

In conclusion, there are several ways to show tables in PostgreSQL. The \dt command is the simplest and easiest way to show tables in the current database. The SELECT statement can be used to retrieve a list of tables using the information_schema.tables view. The pg_catalog.pg_tables view can also be used to show tables in the current database. With these methods, you can easily view the tables in a PostgreSQL database.

In addition to showing tables in a PostgreSQL database, you may also need to perform other operations on the tables, such as creating, altering, and dropping tables.

To create a new table in PostgreSQL, you can use the CREATE TABLE statement. The basic syntax for creating a table is as follows:

CREATE TABLE table_name (
    column1 data_type constraint,
    column2 data_type constraint,
    ...
    columnN data_type constraint
);

For example, to create a table called "employees" with columns for "id", "name", and "salary", you can use the following query:

CREATE TABLE employees (
    id SERIAL PRIMARY KEY,
    name VARCHAR(50) NOT NULL,
    salary NUMERIC(8,2)
);

You can also use the ALTER TABLE statement to modify the structure of an existing table. For example, you can use the ADD COLUMN clause to add a new column to a table, or the DROP COLUMN clause to remove a column from a table.

ALTER TABLE employees ADD COLUMN address VARCHAR(255);

ALTER TABLE employees DROP COLUMN address;

To drop a table in PostgreSQL, you can use the DROP TABLE statement. The basic syntax for dropping a table is as follows:

DROP TABLE table_name;

For example, to drop the "employees" table, you can use the following query:

DROP TABLE employees;

It's important to note that when you drop a table, all the data and the table definition is permanently removed and cannot be recovered. So it's always a good practice to take a backup of the table before dropping it.

In addition to these basic table operations, PostgreSQL also provides several advanced features for managing tables. For example, you can use the WITH (OIDS=FALSE) option to disable the storage of OIDs (object identifiers) for a table, or use the INHERITS clause to create a table that inherits from one or more existing tables. You can also use the CLUSTER command to reorder the data rows of a table based on the values of a specified index.

In this article, we've covered the basics of showing tables in PostgreSQL, as well as how to create, alter, and drop tables. With this knowledge, you should be well equipped to work with tables in your PostgreSQL database.

Popular questions

1. How can I list the tables in a PostgreSQL database using the command line?

You can use the \dt command in the psql command-line interface to list the tables in a PostgreSQL database. Connect to the database using the psql command and type \dt and press enter. This will display a list of tables in the current database.

2. Can I list the tables in a specific schema using the \dt command?

Yes, you can list the tables in a specific schema by adding the schema name after the \dt command. For example, to show the tables in the 'public' schema, you can use the command \dt public.

3. How can I list the tables in a PostgreSQL database using SQL?

You can use the SELECT statement to list the tables in a PostgreSQL database. The information_schema.tables view can be used to retrieve a list of tables in the current database. The following query can be used to show the tables in the current database: SELECT table_name FROM information_schema.tables WHERE table_schema = 'public';

4. How can I add a column to an existing table in PostgreSQL?

You can use the ALTER TABLE statement to add a new column to an existing table. The basic syntax is: ALTER TABLE table_name ADD COLUMN column_name data_type;

5. How can I drop a table in PostgreSQL?

You can use the DROP TABLE statement to drop a table in PostgreSQL. The basic syntax is: DROP TABLE table_name;. It's important to note that when you drop a table, all the data and the table definition is permanently removed and cannot be recovered. So it's always a good practice to take a backup of the table before dropping it.

Tag

PostgreSQL