TABLESAMPLE

PostgreSQL

Example

SELECT * FROM employees TABLESAMPLE BERNOULLI(5);

Output

 emp_id | name   | department
--------+--------+------------
  1001  | John   | Sales
  2002  | Alice  | Marketing
  3003  | Bob    | IT

Explanation

The TABLESAMPLE keyword uses the Bernoulli method to return 5% of the rows in the ‘employees’ table. The result can vary, as the Bernoulli method employs randomness in row selection.

SQL Server

Example

SELECT * FROM Sales.SalesOrderDetail
TABLESAMPLE (10 PERCENT)

Output

SalesOrderID    SalesOrderDetailID  CarrierTrackingNumber  OrderQty    ProductID    ...
43659      517        4911-403C-98        1    776
43659      518        4911-403C-98        3    777
...

Explanation

The TABLESAMPLE clause is used to return a sample percentage of rows from a table. In the example above, we are querying the SalesOrderDetail table from the Sales schema and we are asking for 10% of the rows to be returned. The output shown is a subset of the full table, representing approximately 10% of the entire data set. Please note that the actual number of rows returned by TABLESAMPLE can vary because the function is based on statistical methods.

Oracle

Example

SELECT *
FROM employees
TABLESAMPLE (10);

Output

| EMPLOYEE_ID | FIRST_NAME | LAST_NAME | EMAIL | PHONE_NUMBER | HIRE_DATE | JOB_ID | SALARY | COMMISSION_PCT | MANAGER_ID | DEPARTMENT_ID |
|-------------|------------|-----------|-------|--------------|-----------|--------|--------|----------------|------------|---------------|
| 200         | Jennifer   | Whalen    | JWHALEN| 515.123.4444 | 17-JUN-03 | AD_ASST| 4400   | NULL           | 101        | 10            |
| 202         | Pat        | Fay       | PFAY   | 603.123.6666 | 17-AUG-05 | MK_REP | 6000   | NULL           | 201        | 20            |

Explanation

The TABLESAMPLE clause is used to perform a random sample of the table data. In the provided example, 10% of the rows from ‘employees’ table are selected randomly. The output shows the attributes of the selected employees. Results may vary because of randomness.