What is Query Optimization in SQL?

A query is the statements for interacting with databases and tables. Sometimes we observe the same results with different SQL queries but at that time the selection of best query is an important question and also performance. To access data fast  from your Server or Database it totally depends on your query. That’s why we optimize the query.

How can We Optimize the SQL Query?

We can increase the speed of query or optimize the query with a lot of tricks. Some of the tricks are given below:

  • The SQL query becomes faster if you use the names of the actual columns in a SELECT statement instead of than ‘*’. For Example: Write the query as

SELECT Student_id , fname , lname , age , Department, major

FROM students;

Instead of:

SELECT * FROM students;

  • We used HAVING clause for filter the record after selecting the all records from a given table. But some developers used HAVING clause for other purposes, that means your query will not work faster.

For Example:

SELECT Department , count(Department)

FROM students

WHERE Department ! = ‘ Computer Science ‘  AND major ! = ‘ Computer ‘

GROUP BY Department;

Instead of:

SELECT Department, count(Department)

FROM students
GROUP BY Department
HAVING Department! = ‘ Computer Science ‘  AND major! = ‘ Computer ‘

  • Try to minimize the subqueries, because sometimes you may have more than one subqueries in your main query block. A simple example of this trick is given below:

SELECT fname , lname
FROM customer
WHERE  ( salary , age ) = ( SELECT MAX ( salary ) , MAX ( age ) FROM customer_details ) AND Department = ‘ IT ‘ ;

Instead of:

SELECT fname , lname
FROM customer
WHERE salary = ( SELECT MAX ( salary ) FROM customer_details ) AND               age = ( SELECT MAX ( age ) FROM customer_details ) AND Department = ‘ EE ‘ ;

  • Proper use of these operators in EXISTS, IN, LIKE, AND, OR, UNION, WHERE and COUNT in your query.

Select * from product p
where EXISTS ( select * from order where product.product_id = order.product_id )

Instead of:

Select * from product p
where product_id IN ( select product_id from order )

  • Use carefully UNION clause in your query. For example, a simple query is given below.

SELECT std_id , fname
FROM students UNION ALL ( SELECT std_id , fname FROM programmingTeam ) ;

Instead of:

SELECT std_id , fname
FROM students UNION ( SELECT std_id , fname FROM ProgrammingTeam ) ;

Also a lot of tips and tricks that can help a data administrator to increase the speed and optimize the query.

Optimize the Query According to Database

The query speed and your database performance depends on a lot of factors, your database model, you add or not Indexes in your database and also your query length or kind of query. For example you are retrieving information from one or multiple tables.

What are query optimization techniques?

Query optimization is the overall process of choosing the most efficient means of executing a SQL statement. SQL is a nonprocedural language, so the optimizer is free to merge, reorganize, and process in any order. The database optimizes each SQL statement based on statistics collected about the accessed data.

What is the goal of query optimization?

The goal of query optimization is to choose the best execution strategy for a given query under the given resource constraints. While the query specifies the user intent (i.e., the desired output), it does not specify how the output should be produced.

What are query techniques?

Query optimization techniques in SQL Server: tips and tricks
  • OR in the Join Predicate/WHERE Clause Across Multiple Columns.
  • Over-Indexing a Table.
  • Under-Indexing a Table.
  • No Clustered Index/Primary Key.

How can I improve my SQL skills?

Let’s explore some of them:
  1. Make SQL Part of Your Work Day.
  2. Document Your SQL Learning Experience.
  3. Produce Reports using SQL for your business.
  4. Share Your SQL Knowledge with Others.
  5. Volunteer or Freelance on an SQL or Database Project.
  6. Learn SQL Early in Your Career.
  7. Once You Know SQL, Look at Performance.

How do I optimize multiple joins query?

A few observations: You are performing date manipulations before you join your dates. As a general rule this will prevent a query optimser from using an index even if it exists. You should try to write your expressions in such a way that indexed columns exist unaltered on one side of the expression.

What are the basic steps of query optimizer?

Query optimization involves three steps, namely query tree generation, plan generation, and query plan code generation. A query tree is a tree data structure representing a relational algebra expression. The tables of the query are represented as leaf nodes.

What is physical query plan?

Physical query plan = the (optimized) logical query plan with each node replaced by one or more physical operators used to implement the relational algebra operation.

How does query optimizer work?

The SQL Server Query Optimizer is a cost-based optimizer. It analyzes a number of candidate execution plans for a given query, estimates the cost of each of these plans and selects the plan with the lowest cost of the choices considered.

What is SQL performance tuning?

In a nutshell, SQL performance tuning consists of making queries of a relation database run as fast as possible. As you’ll see in this post, SQL performance tuning is not a single tool or technique. Rather, it’s a set of practices that makes uses of a wide array of techniques, tools, and processes.

How do I select a SQL query?

The SQL SELECT Statement
  1. SELECT column1, column2, FROM table_name;
  2. SELECT * FROM table_name;
  3. Example. SELECT CustomerName, City FROM Customers; Try it Yourself »
  4. Example. SELECT * FROM Customers; Try it Yourself »

What is the purpose of a query processor?

The query processor is the subcomponent of the data server that processes SQL requests. The SQL requests can access a single database or file system or reference multiple types of databases or file systems. Accesses and joins information from multiple data sources and performs updates to a single data source.

What are the main phases of query processing?

➢ Four main Phases: decomposition, optimization, code generation and execution.

What is query performance?

Query performance: The source system on which the virtual table is defined can be too slow for the performance requirements of the data consumers accessing a virtual table. It can also be that the underlying system is just slow by itself. Or the amount of data being accessed is so enormous that every query is slow.

What is SQL process?

SQL processing is the parsing, optimization, row source generation, and execution of a SQL statement. Depending on the statement, the database may omit some of these stages.

What triggers SQL?

Trigger: A trigger is a stored procedure in database which automatically invokes whenever a special event in the database occurs. For example, a trigger can be invoked when a row is inserted into a specified table or when certain table columns are being updated.