PostgreSQL - CREATE TABLE

The PostgreSQL CREATE TABLE statement is used to create a new table. Creating a table involves providing a name to the table and defining name and data type (e.g. varchar, integer, date, etc.) of each column.

Syntax

The syntax of using CREATE TABLE statement in PostgreSQL is given below:

CREATE TABLE table_name (
  column1 datatype,
  column2 datatype,
  column3 datatype,
  .....
  .....
);

Example: Create a table

The mentioned below statement creates a table called Employee which contains five columns: EmpID, Name, City, Age and Salary.

CREATE TABLE Employee (
  EmpID INT NOT NULL PRIMARY KEY,
  Name VARCHAR(255) NOT NULL,
  City VARCHAR(100),
  Age INT,
  Salary DECIMAL(18,2)
);

In the above statement, the data type specifies what type of data the column can hold. After the data type, optional attributes can be provided for each column, like NOT NULL is used to ensure that a column cannot have a NULL value. See PostgreSQL Constraints for more information.

The above statement will create a empty table named Employee containing five columns. When the table is created successfully it displays a message. Along with this, it can also be checked using \d command as follows:

\d Employee;

This will produce the result as shown below:

                     Table "public.employee"
 Column |          Type          | Collation | Nullable | Default 
--------+------------------------+-----------+----------+---------
 empid  | integer                |           | not null | 
 name   | character varying(255) |           | not null | 
 city   | character varying(100) |           |          | 
 age    | integer                |           |          | 
 salary | numeric(18,2)          |           |          | 
Indexes:
    "employee_pkey" PRIMARY KEY, btree (empid)

This indicates that the Employee is now available in the database which can be used to store information related to employee.

Create a table using Another table

The following statements are used to create a table from an existing table:

• CREATE TABLE AS Statement
• SELECT INTO Statement

CREATE TABLE AS Statement

The PostgreSQL CREATE TABLE AS statement is used to create a table from an existing table by copying the existing table's columns. When creating a table in this way, the new table will be populated with the records from the existing table (based on the SELECT statement).

Syntax

The syntax for using CREATE TABLE AS statement in PostgreSQL is given below:

/* copy all columns from a table */
CREATE TABLE new_table
  AS (SELECT * FROM old_table);

/* copy selected columns from a table */
CREATE TABLE new_table
  AS (SELECT column_1, column2, ...
      FROM old_table);

/* copy columns from multiple table */
CREATE TABLE new_table
  AS (SELECT column_1, column2, ...
      FROM old_table_1, old_table_2, ...);

Example:

Consider a database table called Employee with the following records:

• Copy all columns of a table: The below statement is used to create a new table called Employee_PT by copying all columns of Employee table. The new table will contain those records of Employee table where the age of the employee is less than 28.

  CREATE TABLE Employee_PT
    AS (SELECT * FROM Employee
      WHERE Age < 28);
  
  -- see the result
  SELECT * FROM Employee_PT;
  

  
  

  This will produce the result as shown below:

  EmpID	Name	City	Age	Salary
  1	John	London	25	3000
  2	Marry	New York	24	2750
  3	Jo	Paris	27	2800

• Copy selected columns of a table: It is also possible to copy selected columns when using CREATE TABLE AS statement. In the example below, the columns which are copied are: EmpID, Name and City.

  CREATE TABLE Employee_PT
    AS (SELECT EmpID, Name, City FROM Employee
      WHERE Age < 28);
  
  -- see the result
  SELECT * FROM Employee_PT;
  

  
  

  This will produce the result as shown below:

  EmpID	Name	City
  1	John	London
  2	Marry	New York
  3	Jo	Paris

• Using AS clause: The AS clause can be used to rename the column name. See the example below:

  CREATE TABLE Employee_PT
    AS (SELECT EmpID, Name AS EmployeeName, City FROM Employee
      WHERE Age < 28);
  
  -- see the result
  SELECT * FROM Employee_PT;
  

  
  

  This will produce the result as shown below:

  EmpID	EmployeeName	City
  1	John	London
  2	Marry	New York
  3	Jo	Paris

• Copy columns from multiple tables: Consider one more table called Contact_Info with the following records:

  Phone_Number	EmpID	Address	Gender
  +1-8054098000	2	Brooklyn, New York, USA	F
  +33-147996101	3	Grenelle, Paris, France	M
  +31-201150319	4	Geuzenveld, Amsterdam, Netherlands	F
  +86-1099732458	6	Yizhuangzhen, Beijing, China	M
  +65-67234824	7	Yishun, Singapore	M
  +81-357799072	8	Koto City, Tokyo, Japan	M

  
  

  The below statement is used to create a new table called Employee_PT which will contain selected columns of Employee and Contact_Info tables. The new table will contain records based on INNER JOIN.

  CREATE TABLE Employee_PT
    AS (SELECT A.EmpID, A.Name, A.City, B.Address 
      FROM Employee A
      INNER JOIN Contact_Info B
      ON A.EmpID = B.EmpID);
  
  -- see the result
  SELECT * FROM Employee_PT;
  

  
  

  This will produce the result as shown below:

  EmpID	Name	City	Address
  2	Marry	New York	Brooklyn, New York, USA
  3	Jo	Paris	Grenelle, Paris, France
  4	Kim	Amsterdam	Geuzenveld, Amsterdam, Netherlands
  6	Huang	Beijing	Yizhuangzhen, Beijing, China

SELECT INTO Statement

The PostgreSQL SELECT INTO statement is used to create a table from an existing table by copying the existing table's columns. When creating a table in this way, the new table will be populated with the records from the existing table (based on the SELECT statement).

Syntax

The syntax for using SELECT INTO statement in PostgreSQL is given below:

/* copy all columns into new_table */
SELECT *
INTO new_table
FROM old_table
WHERE condition;

/* copy selected columns into new_table */
SELECT column1, column2, column3, ...
INTO new_table
FROM old_table
WHERE condition;

Example:

Consider a database table called Employee with the following records:

• Copy all columns of a table: The below statement is used to copy all columns of Employee table into a new table called Employee_PT. The new table will contain all records of Employee table where the age of the employee is less than 28.

  SELECT * INTO Employee_PT 
  FROM Employee
  WHERE Age < 28;
  
  -- see the result
  SELECT * FROM Employee_PT;
  

  
  

  This will produce the result as shown below:

  EmpID	Name	City	Age	Salary
  1	John	London	25	3000
  2	Marry	New York	24	2750
  3	Jo	Paris	27	2800

• Copy selected columns of a table: It is also possible to copy selected columns when using SELECT INTO statement. In the example below, the columns which are copied are: EmpID, Name and City.

  SELECT EmpID, Name, City INTO Employee_PT 
  FROM Employee
  WHERE Age < 28;
  
  -- see the result
  SELECT * FROM Employee_PT;
  

  
  

  This will produce the result as shown below:

  EmpID	Name	City
  1	John	London
  2	Marry	New York
  3	Jo	Paris

• Using AS clause: The AS clause can be used to rename the column name. See the example below:

  SELECT EmpID, Name AS EmployeeName, City INTO Employee_PT 
  FROM Employee
  WHERE Age < 28;
  
  -- see the result
  SELECT * FROM Employee_PT;
  

  
  

  This will produce the result as shown below:

  EmpID	EmployeeName	City
  1	John	London
  2	Marry	New York
  3	Jo	Paris