Sequence in SQL | Operations sequence in SQL | Query Execution Plan | Hindi

In this video we have discussed the order of execution of any SQL Query. This is an important interview question and everyone should be aware of this concept which will be very helpful in writing queries as well.

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SEQUENCE -

FROM clause: This is where you specify the tables or views from which you want to retrieve data. You identify the data sources that your query will work with.

JOIN operations: If your query involves multiple tables and you need to combine data from these tables, you use JOIN operations. JOINs allow you to connect rows from one table with rows from another table based on related columns.

WHERE clause: After specifying the source tables and performing any necessary joins, you can filter the rows using the WHERE clause. This clause allows you to specify conditions that determine which rows from the tables in the FROM clause should be included in the result set. It's used to narrow down the data set.

GROUP BY clause: If you need to perform aggregate calculations (such as SUM, COUNT, AVG) and group data based on one or more columns, you use the GROUP BY clause. This clause divides the result set into groups of rows based on the specified columns.

HAVING clause: After grouping the data using GROUP BY, you can further filter the grouped results using the HAVING clause. The HAVING clause is similar to the WHERE clause but is applied after grouping, allowing you to filter aggregated data.

SELECT clause: This clause specifies which columns you want to include in the result set. You can select specific columns from the tables, calculate new values using expressions and functions, or use wildcard characters to select all columns.

ORDER BY clause: If you want to control the order in which the rows are returned, you can use the ORDER BY clause. You can sort the result set based on one or more columns, either in ascending (ASC) or descending (DESC) order.

LIMIT/OFFSET or FETCH/FIRST clause: Depending on the database system you're using, you may use LIMIT/OFFSET (common in PostgreSQL and MySQL) or FETCH/FIRST (common in SQL Server and Oracle) to limit the number of rows returned or skip a certain number of rows for pagination.

UNION, INTERSECT, and EXCEPT clauses: If you are working with multiple SELECT statements or combining results from multiple queries, you can use these set operations to combine or compare result sets.

Subqueries and Joins: In more complex queries, you may have subqueries or additional joins to further refine your result set or combine data from multiple sources.

It's important to note that while this is the logical order of operations, the actual execution order may differ based on the query optimizer's decisions in the database management system. The optimizer may rearrange the operations for performance optimization, but the logical order you specify in your SQL query will still be followed in terms of the query's intent.

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