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
SELECT emp_id, count(*) FROM employees GROUP BY emp_id;
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)
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:
Sample Database: employee
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Previous SQL Exercise: List the departments where atleast 2 employees work.
Next SQL Exercise: List the number of employees and average salary.
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