Understanding Interval-based Date Ranges

In this article, we will explore a common problem in database management: handling interval-based date ranges. Specifically, we’ll examine how to merge two tables with overlapping dates while preserving the original data’s integrity.

Table Structure and Data Types

To approach this problem, it’s essential to understand the structure of our tables and the relationships between them. We have two primary tables:

1. Employees’ Career: This table contains information about an employee’s career history, including their start date, end date, year, code mission, employe number, and type.
2. Interruptions: This table stores information about interruptions during work time, such as the start date, end date, year, code mission, employe number, and type.

Both tables use standard date data types (e.g., DATE or DATETIME) to store dates. When working with interval-based ranges, it’s crucial to recognize that these data types can lead to issues when performing calculations or comparisons between dates.

The Problem Statement

Given the two tables, we aim to create a new table that contains all employees’ career information without interruptions. To achieve this, we need to merge the Employees' Career and Interruptions tables while preserving the original data’s integrity.

A Step-by-Step Approach

To solve this problem, we will follow these steps:

1. Create a New Table: We’ll create a new table with columns matching those in our original tables.
2. Merge Data Using Joins: We’ll use LEFT JOINs to join the Employees' Career and Interruptions tables based on common columns (employe number, year, and start date).
3. Update Start and End Dates: If there’s an entry in the Interruptions table for a particular employe number and year, we’ll update the corresponding start or end date in our new table.
4. Insert Remaining Data: We’ll insert any remaining data from the Employees' Career table.

Step 1: Create a New Table

We’ll create a new table called NewTable with columns matching those in our original tables:

CREATE TABLE NewTable (
    startDate DATE,
    endDate DATE,
    year INT,
    codeMission VARCHAR(255),
    employeNumber VARCHAR(255),
    type VARCHAR(255)
);

Step 2: Merge Data Using Joins

Next, we’ll use LEFT JOINs to merge the Employees' Career and Interruptions tables based on common columns (employe number, year, and start date):

INSERT INTO NewTable (
    startDate,
    endDate,
    year,
    codeMission,
    employeNumber,
    type
)
SELECT 
    NVL(i2.endDate+1,e.startDate) AS startDate,
    NVL(i1.startDate-1,e.endDate) AS endDate    
FROM Employee e
LEFT JOIN Interruption i1 ON e.employeNumber=i1.employeNumber AND YEAR(e.startDate)=YEAR(i1.startDate)
LEFT JOIN Interruption i2 ON e.employeNumber=i1.employeNumber AND YEAR(e.endDate)=YEAR(i2.endDate);

Step 3: Update Start and End Dates

If there’s an entry in the Interruptions table for a particular employe number and year, we’ll update the corresponding start or end date in our new table:

INSERT INTO NewTable (
    startDate,
    endDate,
    year,
    codeMission,
    employeNumber,
    type
)
SELECT 
    startDate
FROM Interruption;

Step 4: Insert Remaining Data

Finally, we’ll insert any remaining data from the Employees' Career table:

INSERT INTO NewTable (
    startDate,
    endDate,
    year,
    codeMission,
    employeNumber,
    type
)
SELECT 
    e.startDate,
    e.endDate,
    e.year,
    e.codeMission,
    e.employeNumber,
    e.type
FROM Employee e
WHERE (e.employeNumber, YEAR(e.startDate), YEAR(e.endDate)) NOT IN (
    SELECT i1.employeNumber, YEAR(i1.startDate), YEAR(i1.endDate) 
    FROM Interruption i1
    UNION
    SELECT i2.employeNumber, YEAR(i2.startDate), YEAR(i2.endDate)
    FROM Interruption i2
);

Handling Edge Cases

When working with interval-based ranges, it’s essential to consider edge cases:

• Overlapping Intervals: When two intervals overlap, we need to determine the valid range. In this case, we’ll use the union operator (UNION) to combine the start and end dates of both intervals.
• Gaps in Intervals: If there are gaps in an interval (e.g., a break in employment), we should also consider these gaps when merging data.

Conclusion

In this article, we’ve explored how to merge two tables with overlapping dates while preserving the original data’s integrity. We’ve followed a step-by-step approach using LEFT JOINs and updates to handle various edge cases. By understanding interval-based date ranges and how to work with them, you’ll be better equipped to tackle similar problems in your database management tasks.

Last modified on 2024-01-23