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Improve SQL queries and table creation for department managers and employees #1

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Improve SQL queries and table creation for department managers and employees #1

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139 changes: 55 additions & 84 deletions ...ata Analytics and Business Intelligence/15.SQL Subqueries/15.Employees_SQL_SUBQUERIES.sql
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Original file line number Diff line number Diff line change
@@ -1,108 +1,79 @@
/*Extract the information about all department managers who were hired between the 1st of January 1990 and the 1st of January 1995.*/
-- Extract the information about all department managers who were hired between the 1st of January 1990 and the 1st of January 1995.
SELECT *
FROM dept_manager
WHERE emp_no IN (
SELECT emp_no FROM employees
SELECT emp_no
FROM employees
WHERE hire_date BETWEEN '1990-01-01' AND '1995-01-01'
);

/*Select the entire information for all employees whose job title is “Assistant Engineer”.
Hint: To solve this exercise, use the 'employees' table.*/
-- Select the entire information for all employees whose job title is “Assistant Engineer”.
-- Hint: To solve this exercise, use the 'employees' table.
SELECT *
FROM employees e
WHERE EXISTS(
SELECT emp_no FROM titles t
WHERE title LIKE 'Assistant Engineer'
WHERE EXISTS (
SELECT 1
FROM titles t
WHERE t.title = 'Assistant Engineer'
AND e.emp_no = t.emp_no
);

/*Starting your code with “DROP TABLE”, create a table called “emp_manager”
(emp_no – integer of 11, not null; dept_no – CHAR of 4, null; manager_no – integer of 11, not null). */
-- Starting your code with “DROP TABLE”, create a table called “emp_manager”
-- (emp_no – integer of 11, not null; dept_no – CHAR of 4, null; manager_no – integer of 11, not null).
DROP TABLE IF EXISTS emp_manager;

CREATE TABLE emp_manager(
emp_no INT NOT NULL,
CREATE TABLE emp_manager (
emp_no INT NOT NULL,
dept_no CHAR(4) NULL,
manager_no INT NOT NULL
);


/*Fill emp_manager with data about employees, the number of the department they are working in, and their managers.
Your output must contain 42 rows.*/
INSERT INTO emp_manager
-- Fill emp_manager with data about employees, the number of the department they are working in, and their managers.
-- Your output must contain 42 rows.
INSERT INTO emp_manager (emp_no, dept_no, manager_no)
SELECT
u.*
FROM
(SELECT
a.*
FROM
(SELECT
e.emp_no AS employee_ID,
MIN(de.dept_no) AS department_code,
(SELECT
emp_no
FROM
dept_manager
WHERE
emp_no = 110022) AS manager_ID
FROM
employees e
u.emp_no, u.dept_no, u.manager_no
FROM (
SELECT
e.emp_no AS emp_no,
MIN(de.dept_no) AS dept_no,
110022 AS manager_no
FROM employees e
JOIN dept_emp de ON e.emp_no = de.emp_no
WHERE
e.emp_no <= 10020
WHERE e.emp_no <= 10020
GROUP BY e.emp_no
ORDER BY e.emp_no) AS a UNION SELECT
b.*
FROM
(SELECT
e.emp_no AS employee_ID,
MIN(de.dept_no) AS department_code,
(SELECT
emp_no
FROM
dept_manager
WHERE
emp_no = 110039) AS manager_ID
FROM
employees e

UNION

SELECT
e.emp_no AS emp_no,
MIN(de.dept_no) AS dept_no,
110039 AS manager_no
FROM employees e
JOIN dept_emp de ON e.emp_no = de.emp_no
WHERE
e.emp_no > 10020
WHERE e.emp_no > 10020
GROUP BY e.emp_no
ORDER BY e.emp_no
LIMIT 20) AS b UNION SELECT
c.*
FROM
(SELECT
e.emp_no AS employee_ID,
MIN(de.dept_no) AS department_code,
(SELECT
emp_no
FROM
dept_manager
WHERE
emp_no = 110039) AS manager_ID
FROM
employees e
JOIN dept_emp de ON e.emp_no = de.emp_no
WHERE
e.emp_no = 110022
GROUP BY e.emp_no) AS c UNION SELECT
d.*
FROM
(SELECT
e.emp_no AS employee_ID,
MIN(de.dept_no) AS department_code,
(SELECT
emp_no
FROM
dept_manager
WHERE
emp_no = 110022) AS manager_ID
FROM
employees e
LIMIT 20

UNION

SELECT
e.emp_no AS emp_no,
MIN(de.dept_no) AS dept_no,
110039 AS manager_no
FROM employees e
JOIN dept_emp de ON e.emp_no = de.emp_no
WHERE
e.emp_no = 110039
GROUP BY e.emp_no) AS d) as u;
WHERE e.emp_no = 110022
GROUP BY e.emp_no

UNION

SELECT
e.emp_no AS emp_no,
MIN(de.dept_no) AS dept_no,
110022 AS manager_no
FROM employees e
JOIN dept_emp de ON e.emp_no = de.emp_no
WHERE e.emp_no = 110039
GROUP BY e.emp_no
) u;