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- How to get the current date and time in MySQL?
- To get the current date and time, you should use the NOW() function because it returns the date and time when the statement starts to execute; if it needs to be precise to the time of the function execution moment, use SYSDATE(); use CURDATE() when only the date is needed, and use CURTIME() when only the time is needed; these functions can be used to query, insert or set default values, such as CREATETABLElogs(idINTPRIMARYKEY, messageTEXT, created_atDATETIMEDEFAULTNOW());, NOW() is usually recommended unless the real-time feature of SYSDATE() is required.
- Mysql Tutorial . Database 656 2025-09-02 08:27:01
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- How to find all leaf nodes in a tree structure in MySQL
- Inanadjacencylistmodel,leafnodesarefoundusingaLEFTJOINtoidentifynodeswithoutchildren:SELECTt1.id,t1.nameFROMtreet1LEFTJOINtreet2ONt1.id=t2.parent_idWHEREt2.parent_idISNULL;2.Inanestedsetmodel,leafnodesareidentifiedwherergt=lft 1:SELECTid,nameFROMtree
- Mysql Tutorial . Database 924 2025-09-02 07:51:00
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- How to Import and Export Data from a CSV File in MySQL?
- ToexportdatatoaCSV,useSELECT...INTOOUTFILEwithproperpath,field,andlineformatting,ensuringtheMySQLuserhasFILEprivilegeandtheservercanwritetothespecifiedlocation;2.ToimportdatafromaCSV,useLOADDATAINFILEwithmatchingtablestructureandfielddefinitions,usin
- Mysql Tutorial . Database 299 2025-09-02 06:47:01
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- How to find the last inserted ID in MySQL?
- TofindthelastinsertedIDinMySQL,usetheLAST_INSERT_ID()functionimmediatelyaftertheINSERTstatement;1.Itreturnstheauto-generatedIDfromthemostrecentINSERTinthecurrentsession;2.Itissession-specific,ensuringsafetyinmulti-userenvironments;3.Itpersistsuntilan
- Mysql Tutorial . Database 636 2025-09-02 06:12:01
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- 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(...),(..
- Mysql Tutorial . Database 578 2025-09-02 04:04:01
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- 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.
- Mysql Tutorial . Database 210 2025-09-02 03:54:01
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- What is the SUBSTRING_INDEX() function in MySQL?
- SUBSTRING_INDEX()extractsasubstringfromastringbasedonadelimiterandoccurrencecount,returningtheportionbeforethespecifiednumberofdelimiteroccurrenceswhencountispositiveandafterwhennegative,makingitidealforparsingemailaddresses,filepaths,andURLsinMySQLd
- Mysql Tutorial . Database 744 2025-09-02 02:50:00
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- 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.
- Mysql Tutorial . Database 783 2025-09-02 02:04:00
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- How to get a random row from a MySQL table?
- Forsmalltables,useORDERBYRAND()LIMIT1asitissimpleandeffective.2.Forlargetableswithfewgaps,usetherandomIDmethodbyselectingarandomIDbetweenMINandMAXandfetchingthefirstrowwithWHEREid>=random_valueORDERBYidLIMIT1,whichisfastandefficient.3.Forlargetabl
- Mysql Tutorial . Database 550 2025-09-01 08:18:01
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- 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.
- Mysql Tutorial . Database 772 2025-09-01 08:00:04
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- 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.
- Mysql Tutorial . Database 861 2025-09-01 07:57:01
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- 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
- Mysql Tutorial . Database 943 2025-09-01 07:03:01
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- 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
- Mysql Tutorial . Database 144 2025-09-01 04:12:00
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- 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
- Mysql Tutorial . Database 563 2025-09-01 04:10:00
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