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SQL exercises on employee Database: Check whether all the employees numbers are indeed unique

SQL employee Database: Exercise-103 with Solution

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103. From the following table, write a SQL query to check whether the employees ID are unique or not. Return employee id, number of employees.

Sample table: employees


Sample Solution:

SELECT emp_id,
       count(*)
FROM employees
GROUP BY emp_id;

Sample Output:

 emp_id | count
--------+-------
  69324 |     1
  69062 |     1
  63679 |     1
  67858 |     1
  66564 |     1
  64989 |     1
  67832 |     1
  65646 |     1
  68319 |     1
  68454 |     1
  66928 |     1
  65271 |     1
  68736 |     1
  69000 |     1
(14 rows)

Relational Algebra Expression:

Relational Algebra Expression: Check whether all the employees numbers are indeed unique.

Relational Algebra Tree:

Relational Algebra Tree: Check whether all the employees numbers are indeed unique.

Practice Online


Sample Database: employee

employee database structure

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Previous: From the following tables, write a SQL query to find those departments where at least two employees work. Return department name, number of employees.
Next: From the following table, write a SQL query to find number of employees and average salary. Group the result set on department id and job name. Return number of employees, average salary, department ID, and job name.

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