mysql optimize join statement-Mysql Tutorial-php.cn

Home

Database

Mysql Tutorial

mysql optimize join statement

黄舟

Dec 19, 2016 pm 04:54 PM

Optimize the join statement:
Mysql4.1 begins to support SQL subqueries. This technique allows you to use a SELECT statement to create a single column of query results, and then use this result as a filter condition in another query. Using subqueries can complete many SQL operations that logically require multiple steps to complete at one time. It can also avoid transaction or table locks, and it is also easy to write. However, in some cases, subqueries can be replaced by more efficient joins (JOIN)..
.
Suppose we want to extract all users who do not have order records, we can use the following query to complete this query:
SELECT * FROM customerinfo WHERE CustomerID NOT in (SELECT CustomerID FROM salesinfo)
If you use a connection (JOIN)... to complete this query , the speed will be much faster. Especially if there is an index on CustomerID in the salesinfo table, the performance will be better. The query is as follows:
SELECT * FROM customerinfo LEFT JOIN salesinfoON customerinfo.CustomerID=salesinfo.CustomerID
WHERE salesinfo.CustomerID IS NULL
Connection (JOIN). . The reason why it is more efficient is that MySQL does not need to create a temporary table in memory to complete this logical two-step query.

The above is the content of mysql optimized join statement. For more related content, please pay attention to the PHP Chinese website (www.php.cn)!

Statement

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

MySQL: BLOB and other no-sql storage, what are the differences?May 13, 2025 am 12:14 AM

MySQL'sBLOBissuitableforstoringbinarydatawithinarelationaldatabase,whileNoSQLoptionslikeMongoDB,Redis,andCassandraofferflexible,scalablesolutionsforunstructureddata.BLOBissimplerbutcanslowdownperformancewithlargedata;NoSQLprovidesbetterscalabilityand

MySQL Add User: Syntax, Options, and Security Best PracticesMay 13, 2025 am 12:12 AM

ToaddauserinMySQL,use:CREATEUSER'username'@'host'IDENTIFIEDBY'password';Here'showtodoitsecurely:1)Choosethehostcarefullytocontrolaccess.2)SetresourcelimitswithoptionslikeMAX_QUERIES_PER_HOUR.3)Usestrong,uniquepasswords.4)EnforceSSL/TLSconnectionswith

MySQL: How to avoid String Data Types common mistakes?May 13, 2025 am 12:09 AM

ToavoidcommonmistakeswithstringdatatypesinMySQL,understandstringtypenuances,choosetherighttype,andmanageencodingandcollationsettingseffectively.1)UseCHARforfixed-lengthstrings,VARCHARforvariable-length,andTEXT/BLOBforlargerdata.2)Setcorrectcharacters

MySQL: String Data Types and ENUMs?May 13, 2025 am 12:05 AM

MySQloffersechar, Varchar, text, Anddenumforstringdata.usecharforfixed-Lengthstrings, VarcharerForvariable-Length, text forlarger text, AndenumforenforcingdataAntegritywithaetofvalues.

MySQL BLOB: how to optimize BLOBs requestsMay 13, 2025 am 12:03 AM

Optimizing MySQLBLOB requests can be done through the following strategies: 1. Reduce the frequency of BLOB query, use independent requests or delay loading; 2. Select the appropriate BLOB type (such as TINYBLOB); 3. Separate the BLOB data into separate tables; 4. Compress the BLOB data at the application layer; 5. Index the BLOB metadata. These methods can effectively improve performance by combining monitoring, caching and data sharding in actual applications.

Adding Users to MySQL: The Complete TutorialMay 12, 2025 am 12:14 AM

Mastering the method of adding MySQL users is crucial for database administrators and developers because it ensures the security and access control of the database. 1) Create a new user using the CREATEUSER command, 2) Assign permissions through the GRANT command, 3) Use FLUSHPRIVILEGES to ensure permissions take effect, 4) Regularly audit and clean user accounts to maintain performance and security.

Mastering MySQL String Data Types: VARCHAR vs. TEXT vs. CHARMay 12, 2025 am 12:12 AM

ChooseCHARforfixed-lengthdata,VARCHARforvariable-lengthdata,andTEXTforlargetextfields.1)CHARisefficientforconsistent-lengthdatalikecodes.2)VARCHARsuitsvariable-lengthdatalikenames,balancingflexibilityandperformance.3)TEXTisidealforlargetextslikeartic

MySQL: String Data Types and Indexing: Best PracticesMay 12, 2025 am 12:11 AM

Best practices for handling string data types and indexes in MySQL include: 1) Selecting the appropriate string type, such as CHAR for fixed length, VARCHAR for variable length, and TEXT for large text; 2) Be cautious in indexing, avoid over-indexing, and create indexes for common queries; 3) Use prefix indexes and full-text indexes to optimize long string searches; 4) Regularly monitor and optimize indexes to keep indexes small and efficient. Through these methods, we can balance read and write performance and improve database efficiency.

See all articles