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  • mysql use random order
    mysql use random order
    Using ORDERBYRAND() to implement random sorting is suitable for small data volumes or temporary requirements, but has poor performance. The problem is that the full table scans and generates random numbers for each row and then sorts it, resulting in extremely low efficiency when queries are large data or high-frequency. Alternatives include: 1. Pre-random numbering; 2. Random ID range sampling; 3. Pagination cache; 4. Maintaining random pools separately. Which method to choose depends on business requirements and data structure.
    Mysql Tutorial . Database 777 2025-07-13 02:32:10
  • What is the mark tag for?
    What is the mark tag for?
    The main purpose of mark tags in HTML is to highlight relevant or important text in a document. 1. The most common purpose is to highlight matching keywords in the search result page to help users quickly locate content; 2. It can also be used to emphasize key information in the context, such as definitions, warnings or repeated topics; 3. You can customize the style through CSS and display it in a yellow background by default; 4. When using it, you should pay attention to avoid relying on colors to convey meaning, not overuse, and not affecting screen readers and other auxiliary tools; 5. It is not used for purely decorative purposes. In other cases, more suitable tags such as del, ins, strong or span should be selected.
    HTML Tutorial . Web Front-end 832 2025-07-13 02:31:31
  • What are custom data attributes and how are they used in html5?
    What are custom data attributes and how are they used in html5?
    CustomdataattributesinHTML5shouldbeusedtostoresmall,non-sensitivepiecesofdatadirectlyinHTMLforaccessbyJavaScriptorCSS.1.TheyareidealforstoringitemIDs,UIstates,orconfigurationoptions.2.AccessthemviagetAttribute()orthedatasetpropertyinJavaScript,withda
    HTML Tutorial . Web Front-end 821 2025-07-13 02:28:42
  • mysql transaction commit rollback
    mysql transaction commit rollback
    Transactions are the mechanism in MySQL to ensure data consistency, and have ACID characteristics (atomicity, consistency, isolation, and persistence). The core is to ensure that a set of SQL operations are either successful or all failed. commit is used to confirm all changes in the transaction and write to the database, and rollback is used to undo operations in the transaction and restore to the initial state. Note when using: 1. The default automatic commit needs to be closed for manual control; 2. Transactions cannot be nested, but partial rollback can be simulated by save points; 3. Long transactions affect performance as short as possible; 4. DDL statements will implicitly submit transactions; 5. Forgot to commit or the exception is not processed may lead to lock waiting or data inconsistency; 6. Multi-connection operations need to pay attention to transaction independence. Master these
    Mysql Tutorial . Database 223 2025-07-13 02:26:11
  • How to play a sound on a button click using HTML and JavaScript?
    How to play a sound on a button click using HTML and JavaScript?
    To make the sound play when the button is clicked, you need to bind the click event and trigger the audio playback. First prepare the audio file such as click-sound.mp3 and make sure the path is correct; then create buttons and hidden tags in HTML; then use JavaScript monitor button to click and call the .play() method to play the audio; if you need to play it repeatedly, you can add audio.currentTime=0; pay attention to browser restrictions, volume settings, cross-domain issues and mobile compatibility.
    HTML Tutorial . Web Front-end 774 2025-07-13 02:25:52
  • Styling links with pseudo-classes: :link, :visited, :hover, :active in css
    Styling links with pseudo-classes: :link, :visited, :hover, :active in css
    Defining link styles in sequence can avoid overwriting problems. The specific steps are: 1. First set the basic styles of: link (not accessed) and: visited (visited); 2. Then add transition effects and underscores through:hover; 3. Use:active (activate) to achieve click sinking or background changes; 4. Pay attention to the need to optimize the touch feedback of: active on the mobile terminal. At the same time, make sure that the color of the visited link has sufficient contrast and keep the overall style simple and unified.
    CSS Tutorial . Web Front-end 594 2025-07-13 02:25:40
  • how to use sqlalchemy with mysql
    how to use sqlalchemy with mysql
    The steps to operate MySQL using SQLAlchemy are as follows: 1. Install dependencies and configure connections; 2. Define the model or use native SQL; 3. Perform database operations through session or engine. First, you need to install sqlalchemy and mysql-connector-python, and then create an engine in the format create_engine('mysql mysqlconnector://user:password@host/database_name'). Then you can describe the table structure by defining the model class and use Base.metadata.create_all(engine)
    Mysql Tutorial . Database 665 2025-07-13 02:24:30
  • mysql temporary table vs memory table
    mysql temporary table vs memory table
    Temporary tables are tables with limited scope, and memory tables are tables with different storage methods. Temporary tables are visible in the current session and are automatically deleted after the connection is disconnected. Various storage engines can be used, which are suitable for saving intermediate results and avoiding repeated calculations; 1. Temporary tables support indexing, and multiple sessions can create tables with the same name without affecting each other; 2. The memory table uses the MEMORY engine, and the data is stored in memory, and the restart is lost, which is suitable for cache small data sets with high frequency access; 3. The memory table supports hash indexing, and does not support BLOB and TEXT types, so you need to pay attention to memory usage; 4. The life cycle of the temporary table is limited to the current session, and the memory table is shared by all connections. When choosing, it should be decided based on whether the data is private, whether high-speed access is required and whether it can tolerate loss.
    Mysql Tutorial . Database 554 2025-07-13 02:23:50
  • How to check if a string is valid JSON in PHP
    How to check if a string is valid JSON in PHP
    The method to verify whether a string is legal in PHP is to use json_decode to judge the parsing result with json_last_error. The specific steps are as follows: 1. Use json_decode to try to parse the string; 2. Check whether there is an error through json_last_error. If JSON_ERROR_NONE is returned, it means that it is legal; 3. For empty strings or simple values such as "null", you need to judge the type according to business needs; 4. If the expected result is an array, you can add is_array verification; 5. When processing unreliable input, it is recommended to use trim to remove the whitespace, and note that single quotes should be replaced with double quotes.
    PHP Tutorial . Backend Development 670 2025-07-13 02:21:31
  • How to include one HTML file in another?
    How to include one HTML file in another?
    To introduce another HTML file into HTML, it can be done in a variety of ways. First, use iframes to embed content, which is suitable for independent modules but is not conducive to SEO and style adaptation; second, use JavaScript to dynamically load HTML fragments, which are flexible and controllable, but are limited by cross-domain problems; third, use server-side inclusion (SSI), which is conducive to SEO but requires server configuration; fourth, it is automatic merging of HTML through construction tools, which is suitable for large projects but has high learning costs. Just choose the right method according to your needs.
    HTML Tutorial . Web Front-end 195 2025-07-13 02:20:52
  • How to get a string between two other strings in PHP
    How to get a string between two other strings in PHP
    To extract content from between two strings, you can use PHP's strpos() and substr() functions to implement it. First, find the position of the starting mark and calculate its end point, then find the starting position of the end mark, and finally use substr() to intercept the intermediate content. 1. Use strpos() to locate the starting mark position, and return an empty string if not found; 2. Calculate the actual starting position after the starting mark; 3. Use strpos() to search for the end mark position from the starting position, and return an empty string if not found; 4. Extract the content of the specified range through substr(). For complex scenarios such as multi-match or nested tags, the regular expression preg_match() or preg_m can be considered
    PHP Tutorial . Backend Development 162 2025-07-13 02:20:30
  • Managing overflow content with css overflow property
    Managing overflow content with css overflow property
    When the content exceeds the container, it is necessary to use the overflow attribute of the CSS. Common scenarios include too long pop-up windows, truncated card information, and displaying some content in fixed height areas. How to use: 1. overflow: visible default overflow displays external; 2. overflow:hidden hides overflow content; 3. overflow:scroll always displays scroll bars; 4. Overflow:auto automatically displays scroll bars when it exceeds. Implementing the ellipsis effect requires other attributes: use white-space:nowrap and text-overflow:ellipsis to achieve single line omission, and use -webkit-line-clam to omit multiple line omissions
    CSS Tutorial . Web Front-end 505 2025-07-13 02:18:20
  • Explain the use cases for php Closures and Anonymous Functions.
    Explain the use cases for php Closures and Anonymous Functions.
    ClosuresandanonymousfunctionsinPHPareusefulforwritingcleaner,moreexpressivecode.1.Theyserveascallbacksinarrayfunctionslikearray_mapandarray_filter,allowinginlinelogicwithoutdefiningseparatefunctions.2.Theyenabledelayedexecutionandencapsulation,mainta
    PHP Tutorial . Backend Development 130 2025-07-13 02:17:00
  • Securing MySQL installations with SSL/TLS connections
    Securing MySQL installations with SSL/TLS connections
    To configure MySQL's SSL/TLS encrypted connection, first generate a self-signed certificate and correctly configure the server and client settings. 1. Use OpenSSL to generate CA private key, CA certificate, server private key and certificate request, and sign the server certificate yourself; 2. Place the generated certificate file in the specified directory, and configure the ssl-ca, ssl-cert and ssl-key parameters in my.cnf or mysqld.cnf and restart MySQL; 3. Force SSL on the client, restrict users from connecting only through SSL through the GRANTUSAGE command, or specify the --ssl-mode=REQUIRED parameter when connecting; 4. After logging in, execute \s to check SSL status confirmation
    Mysql Tutorial . Database 778 2025-07-13 02:16:02

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