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- What is the difference between LEFT JOIN and RIGHT JOIN in MySQL?
- LEFTJOIN retains all rows on the left table, and RIGHTJOIN retains all rows on the right table. The two can be converted to each other by swapping the table order. For example, SELECTu.name, o.amountFROMuserssuRIGHTJOINordersoONu.id=o.user_id is equivalent to SELECTu.name, o.amountFROMordersoLEFTJOINuserssuONu.id=o.user_id. In actual use, LEFTJOIN is more common and easy to read, so RIGHTJOIN is less used, and the logic should be clear when selecting.
- Mysql Tutorial . Database 1042 2025-09-06 05:54:01
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- How to use the MAX function in MySQL
- TheMAX()functionreturnsthehighestvalueinaspecifiedcolumn.2.Itcanbeusedwithnumericdata,dates,orstrings,returningthelatestdateoralphabeticallylaststring.3.UseMAX()withWHEREtofilterrowsbeforefindingthemaximum.4.UseMAX()withGROUPBYtofindthemaximumvaluepe
- Mysql Tutorial . Database 246 2025-09-06 04:47:01
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- What is a composite primary key in MySQL?
- AcompositeprimarykeyinMySQLusesmultiplecolumnstouniquelyidentifyarow,suchas(student_id,course_id)inanenrollmentstable,wherethecombinationensuresuniquenessbecauseneithercolumnalonecan;thisenforcesNOTNULLconstraintsonbothcolumns,createsasingleclustered
- Mysql Tutorial . Database 586 2025-09-06 03:03:02
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- How to use prepared statements in MySQL
- Using preprocessing statements can effectively prevent SQL injection and improve performance. The answer is to separate SQL structure and data to achieve safe and efficient query execution. 1. In MySQL native commands, use PREPARE, SET, EXECUTE and DEALLOCATE statements to define and execute preprocessing statements, such as PREPAREstmt_nameFROM'SELECT*FROMusersWHEREid=?'; 2. In PHP's MySQLi, use prepare() to create a statement, bind_param() to bind parameters, execute() to execute, and finally close the statement; 3. In PHP's PDO, support naming placeholders such as:id,
- Mysql Tutorial . Database 434 2025-09-05 08:04:01
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- How to force a query to use a specific index in MySQL
- USEINDEXsuggestsanindexbutallowsMySQLtoignoreitifatablescanisbetter;2.FORCEINDEXrequirestheuseofaspecificindexandpreventstablescans,whichcanimproveperformancewhentheoptimizermakespoorchoicesbutmaydegradeperformanceifmisused;3.IGNOREINDEXpreventsMySQL
- Mysql Tutorial . Database 807 2025-09-05 06:53:01
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- How to get a list of columns for a table in MySQL
- To obtain the column name of the MySQL table, there are three methods: 1. Use DESCRIBEtable_name to quickly view the basic information of the column, which is suitable for manual queries; 2. Use SHOWCOLUMNSFROMtable_name to support database and column name filtering, which is suitable for use in scripts; 3. Query the INFORMATION_SCHEMA.COLUMNS table, which can flexibly obtain detailed column information and be used in programmatic scenarios, which is a standard cross-database practice. Just select the appropriate method according to the usage scenario.
- Mysql Tutorial . Database 630 2025-09-05 04:47:01
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- What is the difference between TRUNCATE and DELETE with no WHERE clause?
- TRUNCATEisfasterandmoreefficientthanDELETEwithnoWHEREclausebecauseitdeallocatesdatapagesandminimallylogstheoperation,whileDELETElogseachrowdeletionindividually,makingitslower;TRUNCATEresetsidentitycounters,doesnotfiretriggers,andmayberestrictedbyfore
- Mysql Tutorial . Database 345 2025-09-05 04:35:01
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- How to change a user's password in MySQL
- ForMySQL5.7.6andlater,useALTERUSER'username'@'host'IDENTIFIEDBY'new_password';2.Forolderversions,useSETPASSWORDFOR'username'@'host'=PASSWORD('new_password');3.Tochangeyourownpassword,useALTERUSERUSER()IDENTIFIEDBY'new_password';4.Alternatively,usethe
- Mysql Tutorial . Database 200 2025-09-05 04:29:01
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- What is the role of the database administrator in MySQL?
- ADBAsetsupandconfiguresMySQLinstanceswithoptimalversions,storageengines,andconfigurationparameterstopreventperformanceissues.2.Theymanageuseraccessandsecuritybycreatingaccounts,assigningprivileges,enforcingpasswordpolicies,andmonitoringforunauthorize
- Mysql Tutorial . Database 917 2025-09-05 04:12:01
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- Benchmarking MySQL Performance: Tools and Methodologies
- The key to MySQL performance benchmarking is to select the right tools and methods and develop scientific testing plans. 1. Common tools include sysbench (suitable for OLTP stress testing), mysqlslap (lightweight official tool), HammerDB (graphical enterprise-level testing) and JMeter (flexible database stress testing); 2. The test plan needs to clarify the goals, set parameters, use real data, and control variables to ensure accuracy; 3. Pay attention to core indicators such as QPS/TPS, response time, resource usage, and error rate; 4. The test environment should be close to production, maintain hardware consistency, network stability, shut down interfering services, multiple runs to average, and avoid direct testing in the production environment.
- Mysql Tutorial . Database 1055 2025-09-05 02:27:01
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- How to use RANK() and DENSE_RANK() in MySQL
- MySQL supports RANK() and DENSE_RANK() window functions since version 8.0, but was not supported in the previous version. 1. RANK() gives the same ranking when the values ??are equal, but subsequent rankings create gaps; 2. DENSE_RANK() ranks the same when the values ??are equal and there is no gaps in the future; 3. You can sort by group through PARTITIONBY; for versions below MySQL8.0, variable simulation is required. It is recommended to upgrade to obtain complete support. Use SELECTVERSION() to check the version to ensure that the window function function is correctly applied.
- Mysql Tutorial . Database 709 2025-09-05 01:41:00
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- How to use the NOW function in MySQL
- NOW() returns the current date and time, which is often used to record the exact moments of data operations; 1. It can be used directly in SELECT, such as SELECTNOW() to get the current timestamp; 2. Automatically record the creation time in INSERT, and supports setting DEFAULTNOW() to achieve automatic filling; 3. Automatically update and modify time in UPDATE combined with ONUPDATENOW(); 4. Compared with other functions, NOW() returns the local date and time, CURDATE() returns the date, CURTIME() returns the time, and UTC_TIMESTAMP() returns the UTC time; when using it, make sure that the field type is DATETIME or TIMESTAMP, and it is recommended to
- Mysql Tutorial . Database 451 2025-09-04 08:51:01
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- How to use the INSERT IGNORE statement in MySQL?
- INSERTIGNOREinMySQLallowsinsertingrowswhilesilentlyskippingerrorslikeduplicatekeysorinvaliddata,makingitidealforensuringrecordsexistwithoutduplicates.1)Useitwhenyouwanttoinsertarowonlyifitdoesn’talreadyexistbasedonuniqueorprimarykeyconstraints.2)Itpr
- Mysql Tutorial . Database 766 2025-09-04 08:23:01
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- What is the purpose of the ON DUPLICATE KEY UPDATE statement in MySQL?
- TheONDUPLICATEKEYUPDATEstatementinMySQLallowsanINSERToperationtoupdateanexistingrowifaduplicateuniqueorprimarykeyisfound,avoidingerrorsandenablingefficientupserts;whenaduplicateisdetected,thespecifiedcolumnsareupdatedusingtheVALUES()functiontoreferen
- Mysql Tutorial . Database 387 2025-09-04 08:21:00
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