Conditional Join

DBMS or Database Management Systems consist of data collected from various sources. Database administrators and analysts use this data to analyze the collected data. Database administrators execute the query through which some output is generated, the conditions are passed through the query. This query can vary from simple to complex query. Joins in a database management system is the concept where the data is been retrieved from more than two tables.

So there is the advanced concept of the database management system which is Conditional Join, which is helpful for database administrators to define the custom query or the complex query having various functions like aggregation functions comparison operators, logical operators, etc. So in this article, we will understand the concept of conditional join. We will see the uses of conditional join. Later we will understand the concept through a simple example.

What is a Conditional Join?

Conditional Join in DBMS is the concept where the database administrators have the provision to design a complex query, which includes conditions, including aggregative functions that can return some values, or which can perform mathematical calculations, These conditional joins also allow various types of operators to be used in the query, like logical orbitals, comparison operators, etc.

Uses of Conditional Join

• Record Filtering: Data stored in the tables, may not be completely useful for analysis, so by using the Conditional Join in the query formation, we can retrieve the only data which can be helpful in analysis.
  
• Aggregating Data: If the data is in numerical format, then the aggregating functions can be applied to the database to get the results in the form of numerical value. We can use SUM, AVG, MIN, etc functions to get the absolute value as the result.
  
• Handling Missing Data: Conditional join in DBMS can be also helpful in handling missing or incomplete data. We can apply proper conditions and remove missing or incomplete data from the tables and database.

Operators Used in Conditional Join

Below mentioned are the operators that are used in the conditional join.

Comparison Operators

Comparison operators are used to compare Values and are used to specify conditions in the where clause of the conditional join query.

• (>): Greater Than Comparison Operator
• (<): Less Than Comparison Operator
• (>=): Greater Than or Equal to Comparison Operator
• (<=): Less Than or Equal to Comparison Operator
• (=): Equal To Comparison Operator
• (!= or <>): Not Equals To Comparison Operator

Logical Operators

Logical operators in Conditional Join are used to combine multiple conditions.

• AND: And operator combines two or more conditions and requires all conditions to be true for a row that is to be included in the output.
  
• OR: Mod logical operator combines two or more conditions and requires at least one condition to be true for a row that is to be included in the output.
  
• NOT: This is also known as the negation operator, which excludes rows that satisfy the negation condition.

Aggregation Function used in Conditional Join

Aggregation functions in conditional join are used to perform mathematical calculations on the subsets of records that meet the specific condition. It summarised the data and returns a single value for each group of rows.

• COUNT: This function returns the total number of rows that satisfy the condition which was specified by the user in the query.
  
• SUM: This function returns the addition of the row data for the given condition by the user.
  
• AVG: This function returns the average of the row data for the given condition by the user.
  
• MIN: This function returns the minimum value as the output for the given condition.
  
• MAX: This function returns the maximum value as the output for the given condition.

Example of Conditional Join

Let us understand the Conditional Join concept using an example.

Consider the below tables (Orders and OrderItems).

Table 1: Order_Data Table

Table 2: Items_Data Table

Query for Conditional Join

SELECT o.CustomerID, SUM(oi.Quantity) AS TotalQuantitySell
FROM Orders_Data o
INNER JOIN Items_Data oi ON o.OrderID = oi.OrderID
WHERE o.OrderDate > '2023-07-16'
GROUP BY o.CustomerID;

Output:

Explanation: In the above example, we have got the result, where we used the comparison operator in the where clause of the query. Along, with this, we have also used the SUM function that calculates the total value of items sold for the individual customer.