mysql-date-gaps

ChatGPT Practical Example: Solving MySQL Challenge by Finding Date Gaps

Requirements

Use of Chat GPT to solve practical challange in relational database mysql.

Description

Assume we have many employees.

• Each employee has many contracts.
• Each contract is composed of a start date and an end date.
• Some employees have been working continuously, while some other employees have a gap in between two or more contracts.

We are looking to:

• Write mysql query that shows the number of days under no contracts (gap of contracts) somewhere between their first and last contract.
• Write mysql query that gives the first ever start date for each employee since the beginning of their employment, OR since the last gap in their contracts.

Examples data and query results:

employeeId	startdate	enddate
1	2020-01-01	2020-12-31
1	2021-01-01	2021-12-31
1	2022-01-01	2022-12-31
2	2020-01-01	2020-12-31
2	2021-01-01	2021-11-30
2	2022-01-01	2022-12-31
3	2020-04-30	2020-12-31
3	2021-01-01	2021-11-30

Solution

mysql Create/Insert Statemets

-- Create the contracts table
CREATE TABLE contracts (
    employeeid INT,
    startdate DATE,
    enddate DATE
);

-- Insert data into the contracts table
INSERT INTO contracts (employeeid, startdate, enddate)
VALUES
    (1, '2020-01-01', '2020-12-31'),
    (1, '2021-01-01', '2021-12-31'),
    (1, '2022-01-01', '2022-12-31'),
    (2, '2020-01-01', '2020-12-31'),
    (2, '2021-01-01', '2021-11-30'),
    (2, '2022-01-01', '2022-12-31'),
    (3, '2020-04-30', '2020-12-31'),
    (3, '2021-01-01', '2021-11-30');

Query 1 - Number of days under no contracts (gap of contracts)

Query:

SELECT 
    employeeid,
    COALESCE(
        DATEDIFF(
            LEAD(startdate) OVER (PARTITION BY employeeid ORDER BY startdate), 
            enddate
        ) - 1, 
        0
    ) AS gap_days
FROM contracts
ORDER BY employeeid, startdate;

Results:

+------------+----------+
| employeeid | gap_days |
+------------+----------+
|          1 |        0 |
|          1 |        0 |
|          2 |       31 |
|          2 |        0 |
|          3 |        0 |
|          3 |        0 |
+------------+----------+

Query 2 - List first ever start date for each employee since the beginning of their employment, OR since the last gap in their contracts.

Query:

SELECT
    employeeid,
    MIN(startdate) AS first_start_date_or_since_gap
FROM (
    SELECT 
        employeeid,
        startdate,
        COALESCE(
            LAG(enddate) OVER (PARTITION BY employeeid ORDER BY startdate) + INTERVAL 1 DAY, 
            '1970-01-01'
        ) AS enddate_plus_one
    FROM contracts
) AS contract_with_lag
WHERE startdate > enddate_plus_one
    OR enddate_plus_one = '1970-01-01'
GROUP BY employeeid;

Results:

+------------+----------------------------+
| employeeid | first_start_date_or_since_gap|
+------------+----------------------------+
|          1 | 2020-01-01                 |
|          2 | 2020-01-01                 |
|          3 | 2020-04-30                 |
+------------+----------------------------+

Use ChatGPT to do all the Work!

See the chat: https://chat.openai.com/share/846020ed-e785-4421-a2ce-eef1eb962777