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  • mysql recursive cte example
    mysql recursive cte example
    MySQL's RecursiveCTE is mainly used to process hierarchical data. 1. It realizes traversal of the tree structure through initial queries and recursive queries, such as finding all subordinates of a certain employee; 2. It can be used to generate numerical sequences, such as 1 to 100; 3. When using them, you need to pay attention to avoid infinite loops, control recursive depth, optimize indexes, and first test small data to verify the correctness of the logic.
    Mysql Tutorial . Database 991 2025-07-12 02:28:40
  • Best Practices for Securing Remote Access to MySQL
    Best Practices for Securing Remote Access to MySQL
    The security of remote access to MySQL can be guaranteed by restricting permissions, encrypting communications, and regular audits. 1. Set a strong password and enable SSL encryption. Force-ssl-mode=REQUIRED when connecting to the client; 2. Restrict access to IP and user rights, create a dedicated account and grant the minimum necessary permissions, and disable root remote login; 3. Configure firewall rules, close unnecessary ports, and use springboard machines or SSH tunnels to enhance access control; 4. Enable logging and regularly audit connection behavior, use monitoring tools to detect abnormal activities in a timely manner to ensure database security.
    Mysql Tutorial . Database 386 2025-07-12 02:25:11
  • mysql find duplicate records in a table
    mysql find duplicate records in a table
    Repetition checking can be implemented in MySQL through GROUPBY and HAVING; single-field repeated use of SELECT field COUNT and grouped, such as SELECTemail, COUNT(*)FROMtableGROUPBYemailHAVINGCOUNT>1; multiple fields need to be grouped at the same time, such as SELECTname, birthdayFROMtableGROUPBYname, birthdayHAVINGCOUNT>1; if specific records are required, you can combine JOIN query; performance optimization includes adding composite indexes, limiting query scope and using LIMIT to reduce data scans.
    Mysql Tutorial . Database 135 2025-07-12 02:23:50
  • Using Common Table Expressions (CTEs) in MySQL 8
    Using Common Table Expressions (CTEs) in MySQL 8
    CTEs are a feature introduced by MySQL8.0 to improve the readability and maintenance of complex queries. 1. CTE is a temporary result set, which is only valid in the current query, has a clear structure, and supports duplicate references; 2. Compared with subqueries, CTE is more readable, reusable and supports recursion; 3. Recursive CTE can process hierarchical data, such as organizational structure, which needs to include initial query and recursion parts; 4. Use suggestions include avoiding abuse, naming specifications, paying attention to performance and debugging methods.
    Mysql Tutorial . Database 808 2025-07-12 02:23:11
  • what is mysql query cache
    what is mysql query cache
    MySQLQueryCache is a built-in caching mechanism used to cache query statements and their results to improve the performance of duplicate queries. 1. It avoids repeated execution of the same query by directly returning cached results; 2. The cache is based on a complete SQL statement, and statement differences or table data changes will cause cache failure; 3. MySQL8.0 has completely removed this function due to poor concurrency performance, low hit rate and high maintenance costs; 4. Alternative solutions include using Redis/Memcached, database middleware ProxySQL, page cache and other more flexible and efficient caching strategies.
    Mysql Tutorial . Database 112 2025-07-12 02:20:51
  • Applying Aggregate Functions and GROUP BY in MySQL
    Applying Aggregate Functions and GROUP BY in MySQL
    The aggregation function is used to perform calculations on a set of values ??and return a single value. Common ones include COUNT, SUM, AVG, MAX, and MIN; GROUPBY groups data by one or more columns and applies an aggregation function to each group. For example, GROUPBYuser_id is required to count the total order amount of each user; SELECTuser_id, SUM(amount)FROMordersGROUPBYuser_id; non-aggregated fields must appear in GROUPBY; multiple fields can be used for multi-condition grouping; HAVING is used instead of WHERE after grouping; application scenarios such as counting the number of classified products, maximum ordering users, monthly sales trends, etc. Mastering these can effectively solve the number
    Mysql Tutorial . Database 257 2025-07-12 02:19:01
  • Implementing foreign key constraints and cascade actions in MySQL
    Implementing foreign key constraints and cascade actions in MySQL
    ToimplementforeignkeysandcascadeactionsinMySQL,useInnoDBtables,definerelationshipswithproperconstraints,andspecifyONDELETEorONUPDATECASCADEbehavior.1)EnsurebothtablesusetheInnoDBengine;2)Createaforeignkeythatreferencesaprimaryoruniquekeyinanothertabl
    Mysql Tutorial . Database 179 2025-07-12 02:17:21
  • Describe the differences between using `echo`, `print`, and `print_r` in php.
    Describe the differences between using `echo`, `print`, and `print_r` in php.
    In PHP, echo, print, and print_r are used to output data but have different uses. 1. echo is used to quickly output one or more strings, with no return value, suitable for outputting plain text or string variables; 2. print is similar to echo but returns 1, and can be used as an expression, but has a slightly poor performance; 3. print_r is used for debugging, can output arrays and objects in an easy-to-read format, and can use the second parameter to decide whether to return the result instead of directly output.
    PHP Tutorial . Backend Development 133 2025-07-12 02:15:31
  • mysql error 1205 lock wait timeout exceeded
    mysql error 1205 lock wait timeout exceeded
    MySQL error 1205: The core reason for Lockwaittimeoutexceeded is that the time when a transaction waits for a lock exceeds the set threshold (default 50 seconds), which is often caused by fierce resource competition, excessive transaction execution or failure to commit, and excessive lock range due to no appropriate index. Troubleshooting methods include: 1. Use SHOWENGINEINNODBSTATUS\G and information_schema.innodb_trx to view active transactions and lock waiting conditions; 2. Use PROCESSLIST to locate stuck SQL; 3. Adjust the innodb_lock_wait_timeout parameter as a temporary mitigation measure; 4. Optimize SQL and transactions
    Mysql Tutorial . Database 378 2025-07-12 02:14:31
  • What are PHP PSR standards and why are they important?
    What are PHP PSR standards and why are they important?
    PSRstandardsareasetofcodingguidelinescreatedbyPHP-FIGtopromoteconsistencyandinteroperabilityacrossPHPprojects.TheyincludePSR-1,whichcoversbasiccodingstandardslikeproperuseofPHPtagsandnamingconventions;PSR-4,whichdefinesanautoloadingstandardforclassfi
    PHP Tutorial . Backend Development 771 2025-07-12 02:14:11
  • PHP str_replace using an array for search and replace
    PHP str_replace using an array for search and replace
    PHP's str_replace function supports batch replacement of strings through arrays. 1. One-to-one replacement: Set $search and $replace as arrays, replace one by one in order, such as ['apple','banana'] with ['fruit A','fruit B']; 2. Unified replacement: $search is an array, $replace is a single string, and all matches are replaced with this string, such as ['cat','dog','bird'] with 'animal'; 3. Notes: str_replace is case sensitive, and str_ireplace can ignore case; the replacement order affects the result, and the first match is preferred.
    PHP Tutorial . Backend Development 494 2025-07-12 02:13:51
  • What is the CSS calc() function and what are its use cases?
    What is the CSS calc() function and what are its use cases?
    TheCSScalc()functionenablesdynamicmathematicalcalculationswithinstylesheets.Itsupportsoperationslikeaddition,subtraction,multiplication,anddivision,allowingdeveloperstomixunitsandadjustsizesonthefly.1.Alwaysusespacesaround and-operators.2.Itsimplifie
    CSS Tutorial . Web Front-end 681 2025-07-12 02:13:41
  • Implementing smooth scrolling experiences with CSS Scroll Snap
    Implementing smooth scrolling experiences with CSS Scroll Snap
    CSSScrollSnap can create a smooth scrolling experience, suitable for scenes such as horizontal sliding, paging scrolling, etc. 1. Set the container to use overflow and scroll-snap-type, and add scroll-snap-align to achieve alignment in the child; 2. The scrolling direction can be selected as x or y axis, and the adsorption behavior is controlled through mandatory or proximity; 3. Common problems include unclear container size, child not full of viewport or abnormal stacking context, fixed size and min-width/height should be set; 4. Combined with scroll-behavior to achieve smooth scrolling, and combined with overscroll-behavior to control the boundary
    CSS Tutorial . Web Front-end 859 2025-07-12 02:13:21
  • PHP strip_tags how to allow some tags
    PHP strip_tags how to allow some tags
    strip_tags can specify the reserved HTML tags through the second parameter. For example, strip_tags($input,'') can retain and tag. Common retained tags include,,,,,,, and (need to be used with caution). When using, you should avoid retaining,,, and other dangerous tags, and pay attention to the security of src. In actual applications, it is recommended to test and combine functions such as htmlspecialchars to ensure security.
    PHP Tutorial . Backend Development 468 2025-07-12 02:12:41

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