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Technical Articles

Database

Mysql Tutorial

What is a primary key in MySQL?

AprimarykeyinMySQLisacolumnorsetofcolumnsthatuniquelyidentifieseachrow,ensuringdataintegritybyenforcinguniquenessandprohibitingnullvalues;itmustbeunique,notnull,limitedtoonepertable(thoughitcanspanmultiplecolumns),andautomaticallycreatesaclusteredind

Aug 18, 2025 am 11:14 AM

What is database normalization in MySQL?

NormalizationinMySQLisadatabasedesignprinciplethatorganizestablestoreduceredundancyandimprovedataintegritybyeliminatingduplicatedataandensuringproperdependencies.Itinvolvesdividinglargetablesintosmaller,relatedonesandlinkingthemthroughkeys,followinga

Aug 18, 2025 am 10:32 AM

mysql 數(shù)據(jù)庫規(guī)范化

How to create a database in MySQL?

To create a MySQL database, first use mysql-uusername-p to log in to the server, and then execute the CREATEDATABASEdatabase_name; command to create a database, such as CREATEDATABASEmyapp_db; to avoid duplicate name errors, use CREATEDATABASEIFNOTEXISTSmyapp_db;, and then select the database through USEmyapp_db;, optionally specify the character set and proofreading rules at creation time such as CREATEDATABASEmyapp_dbCHARACTERSETutf8mb4COLLATEutf8mb4_unic

Aug 18, 2025 am 10:02 AM

How to extract the year, month, or day from a date in MySQL

Use the YEAR() function to extract the year, such as SELECTYEAR('2025-04-05') to return 2025; 2. Use the MONTH() function to extract the month (1-12), or MONTHNAME() to obtain the month name, such as SELECTMONTH('2025-04-05') to return 4; 3. Use DAY() or DAYOFMONTH() to extract the date (1-31), DAYOFWEEK() to return the week value (1-7), DAYNAME() to return the week name, such as SELECTDAY('2025-04-05') to return 5, all functions return NULL when the date is invalid or NULL, which can be used in combination with the query

Aug 18, 2025 am 08:57 AM

How to select data from a table in MySQL

To select data from MySQL table, you need to use SELECT statement. The basic syntax is SELECTcolumn1, column2FROMtable_name; 1. List the column names when selecting a specific column, such as SELECTname, emailFROMusers; 2. Select all data to use SELECTFROMusers, but you need to handle large tables with caution; 3. Use WHERE clause to filter the results, such as SELECTname, ageFROMusersWHEREage>25, and support operators such as =, , IN, LIKE, BETWEEN, etc.; 4. Use ORDERBY to sort the results, such as SELECTna

Aug 18, 2025 am 08:42 AM

What is the FIND_IN_SET() function in MySQL?

FIND_IN_SET()returnsthe1-basedpositionofastringinacomma-separatedlist,or0ifnotfound,andisusefulforsearchingdenormalizeddata;however,itrequiresexactmatches,iscase-insensitivebydefault,performspoorlyonlargetablesduetolackofindexsupport,andshouldbeavoid

Aug 18, 2025 am 07:57 AM

How to work with spatial data in MySQL

To use spatial data in MySQL, you need to make sure to use the InnoDB storage engine that supports spatial indexing and enable the spatial function; 1. When creating a table, specify space types such as POINT and SRID4326, and add SPATIALINDEX to improve query performance; 2. Use OGC standard spatial data types such as POINT, LINESTRING, POLYGON, and insert data through ST_PointFromText, pay attention to the coordinate order of longitude and latitude behind; 3. Use ST_Distance_Sphere to calculate the earth's surface distance (unit in meters), use ST_Contains to determine whether the points are in the polygon, or use ORDERBY distance through ORDERBY distance; 3. Use ST_Distance_Sphere to calculate the earth's surface distance (unit in meters), use ST_Contains to determine whether the points are in the polygon, or use ORDERBY distance

Aug 18, 2025 am 07:35 AM

mysql spatial data

How to delete a database in MySQL?

To delete the MySQL database, use the DROPDATABASE statement. This operation will permanently delete the database and all data and must be executed with caution. The basic syntax is DROPDATABASEdatabase_name, such as DROPDATABASEtest_db; if you are not sure whether the database exists, you should use DROPDATABASEIFEXISTSdatabase_name to avoid errors, such as DROPDATABASEIFEXISTSold_project; this operation is irreversible and requires DROP permissions. In the production environment, you should first confirm the database name, back up important data, and pass SHOWDATABA after deletion.

Aug 18, 2025 am 07:06 AM

How to format dates in MySQL

Date formatting in MySQL is implemented through the DATE_FORMAT() function, which uses formatting symbols to customize the date display method. The basic syntax is DATE_FORMAT(date,format); common formatting characters include: %Y (4-bit year), %m (two-digit month), %d (two-digit date), %M (full month name), %b (abbreviated month name), %H (24-hour hours), %i (minutes), %p (AM/PM), etc.; for example, format "2025-03-1514:35:45" to "March15,2025" with '%M%d,%Y', and convert it to "15-Mar-202502:35PM" with '%d-%

Aug 18, 2025 am 06:25 AM

Optimizing MySQL for Big Data Integration

Using the correct storage engine, optimized pattern design, adjusting configuration parameters and continuous monitoring can improve the performance of MySQL processing big data integration. 1. Priority is given to InnoDB that supports transaction and row-level locks; 2. Reasonably design the pattern according to the access mode, moderately anti-standardize and use the index reasonably; 3. Adjust configuration parameters such as buffer pool size, log file size and connection restrictions; 4. Regularly use EXPLAIN, slow query log and other tools to monitor performance and optimize query and lock contention.

Aug 18, 2025 am 05:25 AM

How to store and query IP addresses in MySQL

Use VARBINARY(16) or BIGINT to store IP addresses, 1. Use INTUNSIGNED to pair with INET_ATON()/INET_NTOA() on IPv4, 2. Use VARBINARY(16) to pair with INET6_ATON()/INET6_NTOA() when IPv4/IPv6 is supported at the same time, 3. Avoid using VARCHAR, 4. Create indexes of IP columns to improve query performance, 5. Use binary operations to achieve subnet matching, 6. Normalize IP input at the application layer or through triggers, thereby ensuring efficient storage and query.

Aug 18, 2025 am 03:01 AM

How to use the ORDER BY clause in MySQL

ORDERBY is used to sort the query results in columns, in order of ascending by default, and can specify ASC or DESC; 1. Single-column sort: For example, ORDERBYsalaryDESC is descending by salary; 2. Multi-column sort: For example, ORDERBYdepartmentASC, salaryDESC is first ascending by department, and then descending by salary; 3. Sort by column position: For example, ORDERBY2DESC is descending by second column, but it is not recommended; 4. Process NULL value: NULL is ranked first in ascending by default, and ORDERBYcommissionISNULL and commissionASC can be used to sort NULL later; 5. Sorting strings is affected by character sets, and COLLATE can be used to specify the area.

Aug 18, 2025 am 01:54 AM

mysql order by

What is the difference between NOW() and CURRENT_TIMESTAMP in MySQL?

NOW() and CURRENT_TIMESTAMP return the same result in a SELECT query, but only CURRENT_TIMESTAMP is available for default values and automatic updates in the table definition, and CURRENT_TIMESTAMP complies with SQL standards and supports unbranched syntax, so CURRENT_TIMESTAMP must be used in DDL to avoid errors.

Aug 18, 2025 am 01:35 AM

How to work with JSON data in MySQL?

Use MySQL to process JSON data to directly store, query and operate semi-structured data in relational databases. Since version 5.7, JSON types are supported; columns are defined through JSON data types and legal JSON values are inserted, MySQL will automatically verify the syntax; data can be extracted using JSON_EXTRACT() or -> (returns quoted strings) and ->> (returns unquoted values), such as profile->> "$.city" to obtain city names; support filtering JSON values through WHERE clauses, and it is recommended to use generated columns and indexes to improve performance, such as ADDcityVARCHAR(50)GENERA

Aug 17, 2025 am 11:21 AM

mysql json