﻿ SQL: Check if all the employees numbers are indeed unique

# SQL Exercise: Check if 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)
```

Explanation:

The given query in SQL that selects the "emp_id" and counts the number of times each "emp_id" appears in the 'employees' table. It then groups the results by "emp_id".

Relational Algebra Expression:

Relational Algebra Tree:

## Practice Online

Sample Database: employee

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Previous SQL Exercise: List the departments where atleast 2 employees work.
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