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Technical Articles

Database

Mysql Tutorial

How to Import and Export Data from a CSV File in MySQL?

ToexportdatatoaCSV,useSELECT...INTOOUTFILEwithproperpath,field,andlineformatting,ensuringtheMySQLuserhasFILEprivilegeandtheservercanwritetothespecifiedlocation;2.ToimportdatafromaCSV,useLOADDATAINFILEwithmatchingtablestructureandfielddefinitions,usin

Sep 02, 2025 am 06:47 AM

How to find the last inserted ID in MySQL?

TofindthelastinsertedIDinMySQL,usetheLAST_INSERT_ID()functionimmediatelyaftertheINSERTstatement;1.Itreturnstheauto-generatedIDfromthemostrecentINSERTinthecurrentsession;2.Itissession-specific,ensuringsafetyinmulti-userenvironments;3.Itpersistsuntilan

Sep 02, 2025 am 06:12 AM

How to insert data into a MySQL table?

Use the INSERTINTO statement to insert data into the MySQL table. The basic syntax is INSERTINTOtable_name(column1,column2,...)VALUES(value1,value2,...). You can insert a single row, multiple rows, or insert data from other table query results. For example, INSERTINTOusers(name,email,age)VALUES('JohnDoe','john@example.com',30) to insert a single record, or you can use INSERTINTOusers(name,email,age)VALUES(...),(..

Sep 02, 2025 am 04:04 AM

mysql Data insertion

How to drop a function in MySQL

To delete functions in MySQL, use the DROPFUNCTION statement; 1. Specify the function name: DROPFUNCTIONfunction_name; 2. Optional IFEXISTS to prevent error reporting: DROPFUNCTIONIFEXISTS function_name; 3. Make sure to have ALTERROUTINE permission; 4. Check whether there is a dependency before deletion; 5. You can view existing functions by querying INFORMATION_SCHEMA.ROUTINES; be careful when executing to avoid affecting the production environment.

Sep 02, 2025 am 03:54 AM

mysql

What is the SUBSTRING_INDEX() function in MySQL?

SUBSTRING_INDEX()extractsasubstringfromastringbasedonadelimiterandoccurrencecount,returningtheportionbeforethespecifiednumberofdelimiteroccurrenceswhencountispositiveandafterwhennegative,makingitidealforparsingemailaddresses,filepaths,andURLsinMySQLd

Sep 02, 2025 am 02:50 AM

mysql

How to connect to MySQL using PHP with PDO

Connecting MySQL to PDO using PHP is a safe and flexible method. 1. First set up a DSN containing the host, database name, user name, password and character set, and configure PDO options; 2. Key options include enabling exception mode, setting the associative array to return results, and disabling preprocessing statement simulation to improve security; 3. Use prepare and execute methods to combine placeholders to perform query or insert operations to effectively prevent SQL injection; 4. Use question marks or named parameters to bind data during query to ensure that all user input is processed through the preprocessing mechanism, thereby ensuring the security and maintainability of the application.

Sep 02, 2025 am 02:04 AM

How to get a random row from a MySQL table?

Forsmalltables,useORDERBYRAND()LIMIT1asitissimpleandeffective.2.Forlargetableswithfewgaps,usetherandomIDmethodbyselectingarandomIDbetweenMINandMAXandfetchingthefirstrowwithWHEREid>=random_valueORDERBYidLIMIT1,whichisfastandefficient.3.Forlargetabl

Sep 01, 2025 am 08:18 AM

mysql 隨機(jī)行

What is the maximum number of columns in a MySQL table?

MySQL 8.0.19 and above support the InnoDB table up to 4,096 columns, but the actual number of available columns is limited by row size (about 8,000 bytes), and requires the use of Dynamic or Compressed row format; the upper limit of earlier versions was 1,017 columns; the MyISAM engine supports 4,096 columns but is limited by 65,534 byte row size; despite this, more than tens of columns should be avoided during design, and it is recommended to optimize the structure through normalization, association tables or JSON columns to ensure maintainability and performance.

Sep 01, 2025 am 08:00 AM

How to join tables in MySQL

Table joins in MySQL are implemented through SELECT statement combined with JOIN clause. The main types include: 1.INNERJOIN: Only the matching rows in the two tables are returned; 2.LEFTJOIN: Return all rows in the left table and the right table match rows, if there is no match, the right table field is NULL; 3.RIGHTJOIN: Return all rows in the right table and the left table match rows, if there is no match, the left table field is NULL; 4.FULLOUTERJOIN: MySQL does not directly support it, but can be simulated by LEFTJOIN and RIGHTJOIN combined with UNION; use ON to specify the connection conditions, and it is recommended to use table alias to simplify query. Multi-table connections need to be linked step by step, and it should be ensured that the connection column has been indexed to improve performance.

Sep 01, 2025 am 07:57 AM

mysql table join

What is the difference between ENUM and SET data types in MySQL?

The ENUM type only allows the selection of a single value from a predefined list, which is suitable for single-select scenarios such as state or gender; the SET type allows the selection of zero or more values, which is suitable for multiple-select scenarios such as permissions or tags. ENUM supports up to 65,535 members, and is stored internally with indexes starting at 1; SET supports up to 64 members, and is stored internally in bitmap form, with each value corresponding to a binary bit. Inserting an invalid value in ENUM will report an error or be saved as an empty string, and SET will automatically ignore the invalid value or process it according to SQL mode. For example, ENUM('active','inactive') can only store one state, while SET('read','write') can store the 'read, write' combination. because

Sep 01, 2025 am 07:03 AM

set enum

Implementing MySQL Data Archiving with Partitioning

MySQL data archive can be implemented through partitioning to improve performance and maintenance efficiency. 1. Select the appropriate partitioning strategy: Priority is given to using RANGE partitions to archive by time, such as dividing order data by month; or use LIST partitions to archive by classification. 2. Notes should be paid attention to when designing table structure: Partition fields must be included in primary keys or unique constraints, and queries should be equipped with partition fields to enable partition cropping. 3. Automatic archives can regularly perform deletion of old partitions through scripts, and record logs and check the existence of partitions to avoid mistaken deletion. 4. Limited applicable scenarios: small tables, query without partition fields, cloud database restriction partitioning function, etc., other archive solutions should be considered, such as timed migration of archive tables. Under reasonable design, partition archives can efficiently manage historical data, otherwise it is easy to induce

Sep 01, 2025 am 04:12 AM

How to check the status of a MySQL server

Usemysqladmin-uroot-pstatustogetkeymetricslikeuptime,threads,andqueries,ormysqladminpingtocheckiftheserverisalive;2.Loginwithmysql-uroot-pandrunSHOWSTATUSLIKE'variable_name'toviewspecificserverstatusvariablessuchasUptime,Threads_connected,Queries,and

Sep 01, 2025 am 04:10 AM

How to export a MySQL table to a CSV file?

Use SELECTINTOOUTFILE to export tables as CSV files on MySQL server. It requires FILE permissions and the target path is writable. For example: SELECT*FROMusersINTOOUTFILE'/tmp/users.csv'FIELDSTERMINATEDBY','ENCLOSEDBY'"'LINESTERMINATEDBY'\n'; If there is no server access permission, you can export them through client commands combined with shell redirection or using scripting languages ??such as Python. The scripting method can better handle special characters, encodings and references to ensure data integrity. Therefore, it is recommended to replication

Sep 01, 2025 am 04:08 AM

How to use the REPLACE statement in MySQL?

REPLACE is used in MySQL to insert new rows. If a unique key or primary key conflict occurs, the old row will be deleted first and then inserted new rows; 2. Use scenarios include ensuring that the record exists and can be deleted and reinserted; 3. The syntax supports VALUES, SET and SELECT forms; 4. The example shows that the replacement operation is triggered through the primary key or unique key; 5. Notes: The automatic incrementing ID may change, the trigger will be deleted and then inserted, the performance is low, and data will be lost if the column is not specified; 6. A safer alternative is to use INSERT...ONDUPLICATEKEYUPDATE for updates rather than full row replacement.

Sep 01, 2025 am 01:09 AM

mysql replace