PostgresSQL Tables

• PostgresSQL Tables
  • CREATE Table
    • Syntax
    • Examples
  • DROP Table
    • Syntax
    • Example

CREATE Table

Syntax

Basic syntax of CREATE TABLE statement is as follows −

CREATE TABLE table_name(
    column1 datatype,
    column2 datatype,
    column3 datatype,
    .....
    columnN datatype,
    PRIMARY KEY (one or more columns)
);

CREATE TABLE is a keyword, telling the database system to create a new table. The unique name or identifier for the table follows the CREATE TABLE statement. Initially, the empty table in the current database is owned by the user issuing the command.

Then, in brackets, comes the list, defining each column in the table and what sort of data type it is. The syntax will become clear with an example given below.

Examples

The following is an example, which creates a COMPANY table with ID as primary key and NOT NULL are the constraints showing that these fields cannot be NULL while creating records in this table −

CREATE TABLE COMPANY(
   ID INT PRIMARY KEY     NOT NULL,
   NAME           TEXT    NOT NULL,
   AGE            INT     NOT NULL,
   ADDRESS        CHAR(50),
   SALARY         REAL
);

Let us create one more table, which we will use in our exercises in subsequent chapters −

CREATE TABLE DEPARTMENT(
   ID INT PRIMARY KEY      NOT NULL,
   DEPT           CHAR(50) NOT NULL,
   EMP_ID         INT      NOT NULL
);

You can verify if your table has been created successfully using \d command, which will be used to list down all the tables in an attached database.

testdb-# \d

The above given PostgreSQL statement will produce the following result −

           List of relations
 Schema |    Name    | Type  |  Owner
--------+------------+-------+----------
 public | company    | table | postgres
 public | department | table | postgres
(2 rows)

Use \d tablename to describe each table as shown below −

testdb-# \d company

The above given PostgreSQL statement will produce the following result −

        Table "public.company"
  Column   |     Type      | Modifiers
-----------+---------------+-----------
 id        | integer       | not null
 name      | text          | not null
 age       | integer       | not null
 address   | character(50) |
 salary    | real          |
 join_date | date          |
Indexes:
    "company_pkey" PRIMARY KEY, btree (id)

DROP Table

Syntax

DROP TABLE table_name;

Example

We had created the tables DEPARTMENT and COMPANY in the previous chapter. First, verify these tables (use \d to list the tables) −

testdb=# drop table department, company;

This would produce the following result −

DROP TABLE
testdb=# \d
relations found.
testdb=#

The message returned DROP TABLE indicates that drop command is executed successfully.