How to use join on in sql
JOIN ON in SQL combines records in multiple tables based on common fields. The usage is as follows: Define JOIN type: INNER JOIN, LEFT JOIN, RIGHT JOIN. Specify comparison operators: =, >, <, etc. Specify the connection field: used to match the column names of the two tables
JOIN ON in SQL
What is JOIN ON?
JOIN ON is a SQL statement used to combine records from two or more tables based on one or more fields in common between them.
Usage:
SELECT * FROM table1 JOIN table2 ON table1.key_field = table2.key_field;
Parameters:
- table1 and table2 : The name of the table to be connected
- key_field: The name of the matching field (column) between the two tables
How to use JOIN ON?
- Define JOIN types: The JOIN ON statement can create different JOIN types, such as INNER JOIN, LEFT JOIN and RIGHT JOIN.
- Specify comparison operators: You can specify comparison operators (such as =, >, <) to match records in two tables.
- Specify the join fields: Specify the join fields of the two tables in the ON clause to determine which records should be merged.
Example:
Consider the following two tables:
| Customers | Orders | |
|---|---|---|
| id | ||
| date | ||
| product_id | ||
| quantity |
SELECT * FROM Customers JOIN Orders ON Customers.id = Orders.customer_id;
Advantages:
- Easily combine data from different tables
- Create More complex queries, linking multiple data sets
- Improving performance and reducing the use of subqueries and nested joins
The above is the detailed content of How to use join on in sql. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
What are the BLOB and CLOB data types in SQL?
Aug 07, 2025 pm 04:22 PM
BLOBstoresbinarydatalikeimages,audio,orPDFsasrawbyteswithoutcharacterencoding,whileCLOBstoreslargetextsuchasarticlesorJSONusingcharacterencodinglikeUTF-8andsupportsstringoperations;2.Bothcanhandleuptogigabytesofdatadependingonthedatabase,butperforman
How does the EXISTS operator compare to the IN operator in SQL?
Aug 05, 2025 pm 01:08 PM
UseEXISTSforexistencechecks,especiallywithlargeorcorrelatedsubqueriesandwhenNULLvaluesarepresent,asitstopsatthefirstmatchandhandlesNULLssafely;useINformembershipchecksagainstsmall,known,ornon-nullvaluesetswherereadabilitymattersandperformanceisnotcri
How do you grant and revoke permissions in SQL?
Aug 04, 2025 am 09:19 AM
GRANTandREVOKEstatementsareusedtomanageuserpermissionsinSQL.1.GRANTprovidesprivilegeslikeSELECT,INSERT,UPDATE,DELETE,ALTER,EXECUTE,orALLPRIVILEGESondatabaseobjectstousersorroles.2.SyntaxforgrantingisGRANTprivilege_typeONobject_nameTOuser_or_role,allo
Optimizing SQL ORDER BY for Query Performance
Aug 04, 2025 am 11:19 AM
To optimize the performance of ORDERBY in SQL, you must first understand its execution mechanism and make rational use of index and query structure. When the sorting field has no index, the database will trigger "filesort", consuming a lot of resources; therefore, direct sorting of large tables should be avoided and the amount of sorted data should be reduced through WHERE conditions. Secondly, establishing a matching index for sorting fields can greatly speed up queries, such as creating reverse order indexes in MySQL 8.0 to improve efficiency. In addition, deep paging (such as LIMIT1000, 10) should be used instead with index-based cursor paging (such as WHEREid>12345) to skip invalid scans. Finally, combining caching, asynchronous aggregation and other means can also further optimize the sorting performance in large data set scenarios.
Understanding SQL Execution Context and Permissions
Aug 16, 2025 am 08:57 AM
SQL execution context refers to the identity or role when running SQL statements, which determine which resources and operation permissions can be accessed. Permission setting should follow the principle of minimum permissions, and common permissions include SELECT, INSERT, EXECUTE, etc. To troubleshoot permission issues, you need to confirm the login name, role permissions, EXECUTEAS settings and schema authorization. Performing context switching can be implemented through EXECUTEAS, but attention should be paid to user existence, permission granting and performance security impact. It is recommended to avoid arbitrarily assigning db_owner or sysadmin roles. The application account should only access necessary objects and be authorized through schema.
How to get the first and last day of the year in SQL?
Aug 11, 2025 pm 05:42 PM
ThefirstdayoftheyearisobtainedbyconstructingortruncatingtoJanuary1stofthegivenyear,andthelastdayisDecember31stofthesameyear,withmethodsvaryingbydatabasesystem;2.Fordynamiccurrentyeardates,MySQLusesDATE_FORMATorMAKEDATE,PostgreSQLusesDATE_TRUNCorDATE_
How to find the sum of a column in SQL?
Aug 08, 2025 pm 05:54 PM
TofindthesumofacolumninSQL,usetheSUM()function,whichreturnsthetotalofallnumericvaluesinaspecifiedcolumnwhileignoringNULLs;1.Usebasicsyntax:SELECTSUM(column_name)ASaliasFROMtable_name;2.Ensurethecolumnhasnumericdatatoavoiderrors;3.ApplyWHEREtofilterro
How to join a table to itself in SQL
Aug 16, 2025 am 09:37 AM
Aself-joinisusedtocomparerowswithinthesametable,suchasinhierarchicaldatalikeemployee-managerrelationships,bytreatingthetableastwoseparateinstancesusingaliases,asdemonstratedwhenlistingemployeesalongsidetheirmanagers'nameswithaLEFTJOINtoincludetop-lev
