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Technical Articles

Database

Mysql Tutorial

How to use FULL OUTER JOIN in MySQL?

MySQL does not support FULLOUTERJOIN, but it can be simulated by combining LEFTJOIN with RIGHTJOIN with UNIONALL, that is, first join left to obtain all left table records, then use right join to filter the records that are not matched in the right table and merge them, thereby returning all the data of the two tables and filling in the NULL value without matching, and finally achieving the result equivalent to FULLOUTERJOIN.

Aug 22, 2025 am 06:43 AM

How to write a recursive CTE in MySQL

MySQL supports recursive CTE starting from version 8.0. 1. The WITHRECURSIVE syntax must be used; 2. The anchor members and recursive members must be connected by UNIONALL; 3. The recursive members must refer to the CTE itself; 4. The termination condition must be set to prevent infinite loops; 5. The recursive depth can be controlled through cte_max_recursion_depth; 6. The use of window functions, GROUPBY, DISTINCT or LIMIT in the recursive part is not supported; 7. It is suitable for hierarchical data queries such as organizational structures. Through examples, digital sequences or employee management chains can be generated. As long as the version requirements are met and the structural specifications are followed, recursive CTE can be used safely.

Aug 22, 2025 am 06:30 AM

How to Create and Use Triggers in MySQL?

AtriggerinMySQLisastoredprogramthatautomaticallyexecutesinresponsetoINSERT,UPDATE,orDELETEeventsonatable.2.TriggersarecreatedusingtheCREATETRIGGERstatementwithBEFOREorAFTERtimingforeachrowaffected.3.UseBEFOREINSERTtovalidateormodifydata,suchasprevent

Aug 22, 2025 am 06:22 AM

How to handle deadlocks in MySQL?

DeadlocksinMySQLoccurwhentransactionsblockeachotherbyholdingneededlocks,butcanbemanagedeffectivelythroughprevention,handling,andmonitoring.1.Minimizedeadlocksbyaccessingrowsinaconsistentorder,keepingtransactionssmallandfast,usinglowerisolationlevelsl

Aug 22, 2025 am 04:25 AM

mysql deadlock

How to use the LIKE operator in MySQL

TheLIKEoperatorinMySQLisusedtosearchforpatternsintextdatausingwildcards;1.Use%tomatchanysequenceofcharactersandtomatchasinglecharacter;2.Forexample,'John%'findsnamesstartingwithJohn,'%son'findsnamesendingwithson,'%ar%'findsnamescontainingar,'\_\_\_\_

Aug 22, 2025 am 12:23 AM

mysql LIKE operator

How to use UNION ALL vs UNION in MySQL

ThekeydifferencebetweenUNIONandUNIONALLinMySQListhatUNIONremovesduplicaterowswhileUNIONALLretainsallrows,includingduplicates;1.UseUNIONwhenyouneeduniqueresultsfromcombinedqueries,asitautomaticallyeliminatesduplicatesandtreatsNULLsasequal;2.UseUNIONAL

Aug 21, 2025 am 11:20 AM

What is the sql_mode ONLY_FULL_GROUP_BY in MySQL?

ONLY_FULL_GROUP_BYexiststopreventambiguousresultsbyrequiringallnon-aggregatedSELECTcolumnstobeintheGROUPBYclause;forexample,withoutit,aquerygroupingbycustomerbutselectingproductwithoutaggregationcouldreturnanarbitraryproductvalue,leadingtomisleadingd

Aug 21, 2025 am 10:58 AM

sql_mode

How to create and use MySQL events

To use MySQL events, you must first enable the event scheduler and then create, manage, and monitor events to automate database tasks. 1. Enable event scheduler: Turn on by executing SETGLOBALevent_scheduler=ON;, if persistence is required, it should be added to the configuration file. 2. Create event: Use the CREATEEVENT statement to define tasks, such as cleaning old logs every day: CREATEEVENTcleanup_old_logsONSCHEDULEEVERY1DAYSTARTSCURRENT_TIMESTAMPDODELETEFROMlogsWHERE created_at

Aug 21, 2025 am 10:38 AM

Scheduled Tasks

How to connect to a remote MySQL server

Enableremoteaccessbysettingbind-address=0.0.0.0inmy.cnfandrestartMySQL;2.CreatearemoteuserwithGRANTALLPRIVILEGESON.TO'username'@'remote_ip'IDENTIFIEDBY'password';3.Allowport3306inthefirewallfortheclientIPorusesecuritygroups;4.Connectfromtheclientusin

Aug 21, 2025 am 10:13 AM

How to get the table size in MySQL?

To check the size of the MySQL table, you can get it by querying information_schema.tables; the specific method is to use a SELECT statement to combine the data_length and index_length fields and convert it into MB units. You can view the data and index sizes for a single table, all tables, or separately. This method is suitable for most cases, but the values ??are approximate. There may be differences for InnoDB tables. The most common and standard way is to query the tables table in the information_schema database to get the results.

Aug 21, 2025 am 10:02 AM

mysql 表大小

Securing MySQL with Network Segmentation

Network segmentation is crucial to MySQL security because it can effectively isolate database services. Specific measures include: 1. Setting a listening address to a local or private IP to restrict external access. 2. Configuring a firewall or security group allows only specific IP access. 3. Strictly manage account permissions to limit login IP and avoid using high-permissions common accounts. Coordinated protection can greatly improve MySQL security.

Aug 21, 2025 am 09:39 AM

How to use RIGHT JOIN in MySQL

Use RIGHTJOIN to get all records in the right table and matching records in the left table, and those that do not match will be displayed as NULL; 1. RIGHTJOIN ensure that every row of the right table appears in the result; 2. The left table is only included when the ON condition matches, otherwise the corresponding field is NULL; 3. Use RIGHTJOIN when the focus is on the right table data; 4. Most developers prefer to use LEFTJOIN and adjust the table order to improve readability; 5. The same results can be implemented by exchanging table order and using LEFTJOIN, so LEFTJOIN is more common in practice.

Aug 21, 2025 am 08:12 AM

How to add a unique constraint to a column in MySQL?

To add unique constraints to columns in MySQL, you can use the ALTERTABLE statement to cooperate with the ADDUNIQUE clause, such as ALTERTABLEusersADDUNIQUE(email). This operation ensures that all values ??in the column are unique. If there is duplicate data, an error will be reported. Therefore, the data needs to be cleaned in advance. The constraint can be specified through ALTERTABLEusersADDCONSTRAINTuk_emailUNIQUE(email) to facilitate subsequent management; it can also be directly defined when creating a table, such as CREATETABLEusers(idINTPRIMARYKEY, emailVARCHAR(255)UNI

Aug 21, 2025 am 07:38 AM

mysql 唯一約束

Optimizing MySQL Query Performance for Large Databases

The key to optimizing the performance of large-scale data query in MySQL database is the rational use of indexes, writing efficient SQL statements, optimizing patterns and data types, and continuously monitoring query performance. 1. Use strategic indexing, prioritize indexing of highly selective columns, avoid over-index, and consider composite indexing; 2. Write efficient queries, select only necessary columns, limit the size of the result set, avoid using functions on indexed columns, and use subqueries with caution; 3. Optimize Schema and data types, select appropriate data types, reasonably standardize design, partition large tables, and ensure that the primary keys are sequential; 4. Monitor and analyze query performance, enable slow query logs, use EXPLAIN to analyze execution plans, and use tools to deeply analyze time-consuming problems to achieve continuous optimization

Aug 21, 2025 am 07:01 AM