Order of Execution in SQL

Last Updated: 15th September, 2024

SQL Query Order of Execution is the arrangement in which a database framework executes SQL queries. It is imperative to understand the order of operations to optimize the execution order of sql queries and dodge errors.

Angelin recently accepted a new role as a Data Analyst for an expansive e-commerce company. She was energetic to learn and develop in her new role but rapidly found herself overpowered by the sum of information she had to work with. After some research and help from her team, Angelin decided to focus on mastering order of execution in SQL query. Angelin began by studying the basics of query execution order and the different methods of execution. Let's help her further.

Making an order is key when it comes to accomplishing a fruitful result. Usually true when preparing a cake, as you would like to preheat the stove, oil the skillet, and blend the fixings in the right order. The same guideline holds genuine when working with SQL queries, as the order of operations can majorly affect how productive and viable the query is.

Order of Execution in SQL (Clauses and Their Functions)

Defining Order of Execution in SQL

The order of query execution in SQL is the order in which the various clauses in a SQL statement are executed. Generally, the order is as follows:

1. FROM clause
2. WHERE clause
3. GROUP BY clause
4. HAVING clause
5. SELECT clause
6. ORDER BY clause
7. LIMIT clause

FROM Clause

The FROM clause is the primary clause in a SQL statement and is utilized to indicate the source tables for the query. It characterizes the table or tables from which the information will be recovered and can incorporate optional join conditions that indicate how the tables ought to be associated.

For illustration, the following query recovers information from the "Customers" and "Orders" tables:

SELECT *
FROM Customers
INNER JOIN Orders
ON Customers.CustomerID = Orders.CustomerID;

WHERE Clause

The WHERE clause is the second clause in a SQL statement and is utilized to indicate criteria for filtering the data. It is utilized to limit the results of a query by applying a filter condition to the information recovered from the source tables.

For illustration, the following query recovers information from the "Customers" table, but only for customers with a CustomerID more prominent than 10:

SELECT *
FROM Customers
WHERE CustomerID > 10;

GROUP BY Clause

The Group BY clause is the third clause in a SQL statement and is utilized to group information according to one or more columns. It is utilized to total the information retrieved from the source tables so that the comes about can be analyzed by grouping the information into categories.

For illustration, the following query recovers information from the "Orders" table and groups it by the "CustomerID" column:

SELECT CustomerID, SUM(TotalPrice)
FROM Orders
GROUP BY CustomerID;

HAVING Clause

The HAVING clause is the fourth clause in a SQL statement and is utilized to indicate conditions that must be met to return comes about.

It is utilized to channel the results of a query after the Group BY clause has grouped the information.

For illustration, the following query recoups information from the "Orders" table, groups it by the "CustomerID" column. It only returns results for customers with a add up to order sum greater than 1000:

SELECT CustomerID, SUM(TotalPrice)
FROM Orders
GROUP BY CustomerID
HAVING SUM(TotalPrice) > 1000;

SELECT Clause

The SELECT clause is the fifth clause in a SQL statement and is utilized to indicate the columns that will be returned within the query results. It is utilized to select which column from the source tables should be included in the query results.

For illustration, the following query recovers the "CustomerName" and "TotalPrice" columns from the "Clients" and "Orders" tables:

SELECT Customers.CustomerName, Orders.TotalPrice
FROM Customers
INNER JOIN Orders
ON Customers.CustomerID = Orders.CustomerID;

ORDER BY Clause

The ORDER BY clause is the sixth clause in a SQL statement and is used to specify the order in which the query results should be returned. It is used to sort the data retrieved from the source tables in either ascending or descending order.

For example, the following query retrieves data from the "Orders" table and orders the results by the "TotalPrice" column in descending order:

SELECT *
FROM Orders
ORDER BY TotalPrice DESC;

LIMIT Clause

The Limit clause is the seventh clause in a SQL statement and is utilized to limit the number of records that will be returned within the query results. It is utilized to restrict the number of rows returned from the source tables, permitting you to indicate a particular number or a range of records to be returned.

For illustration, the following query recovers the first 10 records from the "Orders" table:

SELECT *
FROM Orders
LIMIT 10;

Conclusion

As she continued to learn, Angelin was able to apply her knowledge to her company’s data. She optimized their queries and made them more efficient, saving the company time and money. Now, Angelin is a master order of SQL query execution and is an invaluable asset to her company. She is using her knowledge to help the company better analyze its data and make more informed decisions. Angelin’s dedication to learning and mastering SQL query execution orders has paid off, and she is now an essential part of her team.

Key Takeaways

• SQL queries are evaluated in a particular order, the query execution order.
• To begin with, the FROM clause is assessed, which decides the source of the information that will be utilized within the query.
• Next, the WHERE clause is evaluated to filter the information from the FROM clause.
• The Group BY clause is then assessed to group the information into distinct sets.
• Then, the HAVING clause is evaluated to filter the grouped data.
• Finally, the SELECT and ORDER BY clauses are evaluated to determine the query's output.

Quiz

1. What is the order of SQL query execution?  
   1. SELECT, FROM, WHERE, Group BY, Order BY 
   2. SELECT, FROM, WHERE, Order BY, Group BY 
   3. FROM, SELECT, WHERE, Group BY, Order BY 
   4. FROM, SELECT, WHERE, Order BY, Group BY

Answer: d.  FROM, SELECT, WHERE, Order BY, Group BY

2. What is the order of operations for SQL queries? 
   1. SELECT, JOIN, WHERE, GROUP BY, ORDER BY 
   2. SELECT, FROM, WHERE, GROUP BY, ORDER BY 
   3. SELECT, WHERE, JOIN, GROUP BY, ORDER BY  
   4. SELECT, FROM, WHERE, ORDER BY, GROUP BY

Answer:d. SELECT, FROM, WHERE, ORDER BY, GROUP BY

3. What is the order of operations for a SQL query? 
   1. SELECT, FROM, WHERE, JOIN, ORDER BY  
   2. SELECT, FROM, WHERE, ORDER BY, JOIN 
   3. SELECT, WHERE, JOIN, ORDER BY, FROM 
   4. SELECT, FROM, WHERE, ORDER BY, JOIN

Answer:d. SELECT, FROM, WHERE, ORDER BY, JOIN

4. What is the order of operations for a SQL query? 
   1. SELECT, FROM, WHERE, ORDER BY, GROUP BY 
   2. SELECT, WHERE, FROM, ORDER BY, GROUP BY 
   3. SELECT, FROM, WHERE, GROUP BY, ORDER BY 
   4. SELECT, WHERE, FROM, GROUP BY, ORDER BY

Answer:a. SELECT, FROM, WHERE, ORDER BY, GROUP BY