How to Implement CONNECT BY PRIOR Functionality in MySQL?

CheckQcachestatusvariablesusingSHOWSTATUSLIKE'Qcache%'tomonitorhits,inserts,prunes,andmemoryusage;2.Calculatehitratewith(Qcache_hits/(Qcache_hits Qcache_inserts))*100,aimingfor70–80%orhigher;3.AssessmemoryefficiencybyanalyzingQcache_free_memoryandfra

TolistallusersinMySQL,executeSELECTUser,HostFROMmysql.user;afterlogginginwithsufficientprivileges.2.Fordetailedinformationsuchasauthenticationpluginandaccountstatus,useSELECTUser,Host,authentication_string,plugin,account_locked,password_expiredFROMmy

TofindthelengthofastringinMySQL,useLENGTH()forbytesorCHAR_LENGTH()forcharacters.1.LENGTH()returnsthenumberofbytes,soSELECTLENGTH('Hello')returns5,butSELECTLENGTH('café')returns5inUTF8mb4because'é'uses2bytes.2.CHAR_LENGTH()returnsthenumberofcharacters

To add a primary key to an existing table, use the ALTERTABLE statement with the ADDPRIMARYKEY clause. 1. Ensure that the target column has no NULL value, no duplication and is defined as NOTNULL; 2. The single-column primary key syntax is ALTERTABLE table name ADDPRIMARYKEY (column name); 3. The multi-column combination primary key syntax is ALTERTABLE table name ADDPRIMARYKEY (column 1, column 2); 4. If the column allows NULL, you must first execute MODIFY to set NOTNULL; 5. Each table can only have one primary key, and the old primary key must be deleted before adding; 6. If you need to increase it yourself, you can use MODIFY to set AUTO_INCREMENT. Ensure data before operation

TheSETdatatypeinMySQLstoreszeroormorevaluesfromapredefinedlist,idealformultiplechoiceslikepreferencesortags.2.DefineaSETcolumnbyspecifyingallowedstringvaluesinparenthesesduringtablecreation,suchasSET('email','sms','push','mail').3.Insertvaluesascomma

ALTERTABLEinMySQLisusedtomodifyanexistingtable’sstructure,andthemostcommonoperationsinclude:1.AddingacolumnusingADDCOLUMN,optionallyspecifyingpositionwithAFTERorFIRST;2.DroppingacolumnusingDROPCOLUMN,whichpermanentlyremovesthecolumnanditsdata;3.Modif

Use LIMIT to limit the number of rows returned by the query, such as SELECTFROMemployeesLIMIT5 returns up to 5 rows; 2. Combining ORDERBY can ensure the order, such as SELECTFROMemployeesORDERBYsalaryDESCLIMIT3 to obtain the highest salary of 3 employees; 3. Use OFFSET to implement paging, such as LIMIT5OFFSET10 means skipping the first 10 rows and returning 5 rows, which is equivalent to LIMIT10,5; 4. It is often used to paging, obtain the first N records or data sampling; 5. Note that the order should always be guaranteed with ORDERBY. LIMIT is MySQL-specific syntax, and high offset may affect performance. It is recommended that

First, make sure to enable and correctly configure the slow query log, set slow_query_log=ON, long_query_time=1.0, and log_queries_not_using_indexes=ON, and restart MySQL or dynamic application configuration; 2. Use mysqldumpslow tool to analyze the log, view the most frequent slow query through mysqldumpslow-sc-t10, or filter specific tables with the -g parameter; 3. Use pt-query-digest in PerconaToolkit for in-depth analysis, generate detailed statistics and optimization suggestions, such as identifying that Rows_examined is much larger than Ro