﻿ SQL: List the employees who joined before 1991

SQL Exercise: List the employees who joined before 1991

SQL employee Database: Exercise-12 with Solution

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12. From the following table, write a SQL query to find those employees who joined before 1991. Return complete information about the employees.

Sample table: employees

Pictorial Presentation:

Sample Solution:

``````SELECT *
FROM employees
WHERE hire_date<('1991-1-1');
``````

Sample Output:

``` emp_id | emp_name | job_name | manager_id | hire_date  | salary | commission | dep_id
--------+----------+----------+------------+------------+--------+------------+--------
63679 | SANDRINE | CLERK    |      69062 | 1990-12-18 | 900.00 |            |   2001
(1 row)
```

Explanation:

The said query in SQL that selects all columns from the 'employees' table where the hire_date is before January 1, 1991.

The "WHERE" clause filters the results for all employees whose hire date is earlier than January 1, 1991.

Relational Algebra Expression:

Relational Algebra Tree:

Practice Online

Sample Database: employee

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Previous SQL Exercise: List the employees not in department 2001.
Next SQL Exercise: Average salaries of the employees works as ANALYST.

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SQL: Tips of the Day

Grouped LIMIT in PostgreSQL: Show the first N rows for each group?

```db=# SELECT * FROM xxx;
id | section_id | name
----+------------+------
1 |          1 | A
2 |          1 | B
3 |          1 | C
4 |          1 | D
5 |          2 | E
6 |          2 | F
7 |          3 | G
8 |          2 | H
(8 rows)
```

I need the first 2 rows (ordered by name) for each section_id, i.e. a result similar to:

```id | section_id | name
----+------------+------
1 |          1 | A
2 |          1 | B
5 |          2 | E
6 |          2 | F
7 |          3 | G
(5 rows)
```

PostgreSQL v9.3 you can do a lateral join

```select distinct t_outer.section_id, t_top.id, t_top.name from t t_outer
join lateral (
select * from t t_inner
where t_inner.section_id = t_outer.section_id
order by t_inner.name
limit 2
) t_top on true
order by t_outer.section_id;
```

Database: PostgreSQL

Ref: https://bit.ly/3AfYwZI

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