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How does the database cow optimize SQL?

2022-01-27 04:33:37 InfoQ

SQL  Query optimization reduces the resources required for query and improves the overall system performance , In this paper , We will discuss  SQL  Query optimization 、 How is it done 、 Best practices and their importance .

What is?  SQL  Query optimization ?

SQL  Query optimization is an efficient way to write  SQL  Inquire about , And in terms of execution time and database representation
Improve query performance
Iterative process of , Query optimization is one of several relational database management systems  (RDBMS)  An important function of .

Poorly written queries will consume more system resources , Long execution time , And may result in loss of service .

A query is a question or request for data or information from a database , You need to write a set of predefined code that the database can understand , Structured query language  (SQL)  And other query languages are designed to retrieve or manage data in relational databases .

Queries in a database can be written in many different structures , And can be executed by different algorithms , Poorly written queries will consume more system resources , Long execution time , And may result in loss of service , A perfect query can reduce execution time and bring the best  SQL  performance .

SQL The main purpose of query optimization is :

  • Reduce response time and improve query performance
  • Reduce  CPU  Execution time for faster results
  • Minimize the number of resources used to improve throughput

SQL  How query optimization is accomplished ?

It is important to ensure that the query is in the best path and form ,SQL  The query process requires the best execution plan and computing resources , Because they are  CPU  Intensive operation ,SQL  Query optimization is accomplished through three basic steps :

  • Query resolution
  • Optimize
  • Query execution

Parsing ensures that the query is syntactically and semantically correct , If the query syntax is correct , Then convert it into an expression and pass it to the next step .

Optimization plays an important role in query performance , And it can be difficult , Any query execution plan considering optimization must return the same results as before , But the optimized performance should be improved .

SQL  Query optimization includes the following basic tasks :

  • Detect key components that need to be improved
  • Analyze query execution to find problems causing poor performance
  • Improve query execution plan to optimize query execution

Last , Query execution involves converting the plan generated by the query optimization step into an operation , If nothing goes wrong , This step will return the result to the user .

What are best practices ?

Once the user determines that a query needs to be improved to optimize  SQL  performance , They can choose any optimization method —— Optimize  SQL  There are many ways to query performance , Here are some best practices .

avoid select *

A simple way to improve query performance is to  
SELECT *
  Replace with the actual column name , When developers use... In tables  
SELECT *
  When the sentence is , It will read the available data of each column .

Use  
SELECT  Field name  FROM
  instead of  
SELECT * FROM
  when , You can narrow the range of data extracted from the table during the query , This helps to improve query speed .

Avoid queries in loops

In the loop  SQL  The query is run more than once , This will significantly reduce the running speed , These queries unnecessarily consume memory 、CPU  Capacity and bandwidth , This affects performance , Especially when  SQL  When the server is not on the local computer , Deleting queries within a loop can improve overall query performance .

establish  SQL Server  Indexes

Use SQL  Server indexing can reduce running time and retrieve data faster , You can use aggregate and non aggregate  SQL  Index to optimize  SQL  Inquire about , Nonclustered indexes are stored separately , Need more disk space , therefore , It's important to know when to use indexes .

Use  OLAP  function

The OLAP function “ Expanded SQL Parsing function syntax .” SQL  Medium  OLAP  Faster and easier to use , Familiar with these grammars  SQL  Developers and  DBA  They can be easily adapted and used .

OLAP  Function can create all standard calculation metrics , For example, ranking 、 Mobile aggregation 、 share 、 Beginning to present 、 Early and future periods 、 Parallel period, etc .

Keep statistics up to date

The query optimizer uses statistics to determine how best to join tables 、 When to use indexes and how to access them , Whether it's manual or automatic ,SQL  Server statistics should be kept up to date .

Out of date  SQL Server  Statistics will affect the table 、 Index or column Statistics , And leads to poor query plan performance .

Why?  SQL  Query optimization is important ?

SQL  Query optimization can easily improve system performance , To save money , Optimize  SQL  Queries can improve operational efficiency and speed up performance , So as to improve the online progress of the system .

SQL  Query optimization is important , There are many reasons , Include :

  • stay  SQL  Provide faster results in the database
  • Reduce the processing cost of each query
  • Reduce the query processing pressure of the database
  • Consume less memory for query processing
  • Improve the overall performance of the system

Organizations can achieve reliable data access and high levels of performance through faster response time , Optimize  SQL  Query can not only improve the overall system performance , It can also improve the reputation of the organization , Final ,SQL  Best practices in query optimization help users get accurate results 、 Fast database results .

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