![]() We shall copy the student’s name and address from Attendance table, paste it into a new spreadsheet, In all probability, some of us will start with rollnumber 1 of the studentinfo table If you want to see a student’s name, address, present and attendance date in a new spreadsheet, you can only use one row at a time of a table. The attendance table contains daily attendance of the students this table has the student’s roll number, present, and attendance date columns. StudentInfo table has student’s information it has roll number, name and address columns. For example, how would you match the following data manually, if you have these two tables given below: In relational databases, a JOIN is the mechanism which we use to combine the data set of two or more tables, and a Nested Loop Join is the simplest physical implementation of joining two tables. This article only focuses on the Nested Loop Join, and hence let us quickly move to the joining part. Whenever you join a table to another table logically, the Query Optimizer can choose one of the three physical join iterators based on some cost based decision, these are Hash Match, Nested Loop Join and Merge Join. ![]() ![]() However, in the Execution plan, there are many iterators for different operations, but in this article, we will learn one iterator only, that is, the Nested Loop Join. We need not to worry how things actually happen in the SQL Server, but it’s always good to know what’s happening behind the curtain sometimes so that we can figure out why a query is running slow. Optimizer which is responsible for fulfilling the user requests optimally. Now, it is the responsibility of the database to fulfill the user’s request optimally. SQL is a declarative language we just write a query by the SQL language standard and ask for the database to fulfill the request. All these types of joins that we use are actually based on the requirement of the users. To see the data of two or more tables together, we need to join the tables the joining can be further categorized into INNER JOIN, LEFT OUTER JOIN, RIGHT OUTER JOIN, FULL OUTER JOIN, and CROSS JOIN. A relational database system uses SQL as the language for querying and maintaining databases.
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