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  • mysql substring function
    mysql substring function
    MySQL's SUBSTRING function is used to extract substrings from strings. Its basic syntax is SUBSTRING(str, start, length) or SUBSTRING(strFROMstartFORlength), where str is the original string, start is the starting position (starting from 1), and length is the number of characters to be extracted (optional). 1. If length is omitted when using it, it will be extracted to the end of the string; 2. It is often used to extract specific parts from fields, such as extracting the user ID in the mailbox domain name or path; 3. Pay attention to the index starting from 1, start returning to an empty string beyond the length, and calculate according to characters instead of bytes when processing multi-byte characters; 4.
    Mysql Tutorial . Database 763 2025-07-16 03:06:20
  • mysql performance tuning
    mysql performance tuning
    The key to MySQL performance tuning is to grasp the core direction, which mainly includes the following points: 1. Query statement optimization, enable slow query logs and use EXPLAIN to analyze the execution plan, avoid index failure and unnecessary full table scanning; 2. Reasonably configure MySQL parameters, such as adjusting innodb_buffer_pool_size, max_connections and other parameters to improve IO and concurrency capabilities; 3. Table structure design and indexing strategy to avoid frequent occurrence of large fields in the main table. It is recommended to use self-incremental integers for the primary key, and composite indexes follow the principle of leftmost prefix to avoid blindly adding indexes to increase maintenance costs. By continuously optimizing these aspects, database performance can be effectively improved rather than relying solely on hardware upgrades.
    Mysql Tutorial . Database 492 2025-07-16 03:03:21
  • how to connect excel to mysql database
    how to connect excel to mysql database
    There are three ways to connect Excel to MySQL database: 1. Use PowerQuery: After installing the MySQLODBC driver, establish connections and import data through Excel's built-in PowerQuery function, and support timed refresh; 2. Use MySQLforExcel plug-in: The official plug-in provides a friendly interface, supports two-way synchronization and table import back to MySQL, and pay attention to version compatibility; 3. Use VBA ADO programming: suitable for advanced users, and achieve flexible connections and queries by writing macro code. Choose the appropriate method according to your needs and technical level. PowerQuery or MySQLforExcel is recommended for daily use, and VBA is better for automated processing.
    Mysql Tutorial . Database 853 2025-07-16 02:52:50
  • mysqldump without data (schema only)
    mysqldump without data (schema only)
    To only export the structure (schema) of the MySQL database without exporting the data, the core method is to use the mysqldump command and add the --no-data or -d parameter; 1. This parameter ensures that only table structures, view definitions, etc. are exported, and no data records are not included; 2. To export the structures of multiple databases at once, add the --databases parameter and list all database names; 3. If the database contains stored procedures, triggers or functions, additional --routines and --triggers parameters need to be added to ensure the complete export of structure information.
    Mysql Tutorial . Database 228 2025-07-16 01:51:50
  • how to get table schema in mysql
    how to get table schema in mysql
    To obtain MySQL table structure information, the following methods can be used: 1. Use DESCRIBE or DESC command to view basic information such as field names and types; 2. Use SHOWCREATETABLE to obtain complete table construction statements including indexes, engines and other details; 3. Query the information_schema system database to obtain more detailed metadata such as column annotations and data type length; 4. Use graphical tools such as Navicat and DBeaver to intuitively view and modify the table structure.
    Mysql Tutorial . Database 538 2025-07-16 01:48:52
  • Importing and Exporting Data Using LOAD DATA INFILE or SELECT INTO OUTFILE in MySQL
    Importing and Exporting Data Using LOAD DATA INFILE or SELECT INTO OUTFILE in MySQL
    MySQL provides two efficient data import and export methods: LOADDATAINFILE and SELECTINTOOUTFILE. LOADDATAINFILE can be used to quickly import CSV or TSV files into the database, supporting specified fields and line separators, skipping title lines and field order mapping; SELECTINTOOUTFILE is used to export query results into files, suitable for data backup or cross-system transmission. Note that the file path cannot be repeated and needs to be manually compressed; when using it, you must ensure that MySQL users have FILE permissions and follow the path restrictions of secure_file_priv, otherwise the operation will fail due to permission issues.
    Mysql Tutorial . Database 469 2025-07-16 01:36:20
  • how to add index to mysql table
    how to add index to mysql table
    The situations where indexing is required include: fields are often used for query conditions, JOIN connection, sorting or grouping; the syntax for adding a single column index is ALTERTABLEtable_nameADDINDEXindex_name(column_name), it is recommended to customize naming and avoid peak operations; combined indexes should ensure that leading columns and fields with high distinction are placed in front, not all multi-conditions are suitable; deleting indexes requires confirmation of dependence on SQL to avoid affecting query performance.
    Mysql Tutorial . Database 978 2025-07-16 00:21:11
  • mysqldump single table with where clause
    mysqldump single table with where clause
    The method of using mysqldump to export a single table and add WHERE conditions is as follows: 1. Use the --where parameter to specify the filter conditions, and the syntax is mysqldump-u[username]-p[database_name][table_name]-where="condition">output_file.sql; 2. Note that fields and values need to be quoted correctly, especially when containing spaces or special characters; 3. The default export includes table creation statements, if only data is required, the -t parameter can be added; 4. It is not supported to add different conditions to multiple tables at a time, and it needs to be executed separately. This method is suitable for data backup, migration or retrieval
    Mysql Tutorial . Database 757 2025-07-15 02:42:20
  • mysql incorrect string value for column
    mysql incorrect string value for column
    MySQL error "incorrectstringvalueforcolumn" is usually because the field character set does not support four-byte characters such as emoji. 1. Cause of error: MySQL's utf8 character set only supports three-byte characters and cannot store four-byte emoji; 2. Solution: Change the database, table, fields and connections to utf8mb4 character set; 3. Also check whether the configuration files, temporary tables, application layer encoding and client drivers all support utf8mb4; 4. Alternative solution: If you do not need to support four-byte characters, you can filter special characters such as emoji at the application layer.
    Mysql Tutorial . Database 735 2025-07-15 02:40:01
  • Setting up semi-synchronous replication in MySQL
    Setting up semi-synchronous replication in MySQL
    The steps for setting MySQL semi-synchronous replication are as follows: 1. Confirm the version supports and load the plug-in; 2. Turn on and enable semi-synchronous mode; 3. Check the status and operation status; 4. Pay attention to timeout settings, multi-slave library configuration and master-slave switching processing. It is necessary to ensure that MySQL 5.5 and above versions are installed, rpl_semi_sync_master and rpl_semi_sync_slave plugins, enable corresponding parameters in the master and slave library, and configure automatic loading in my.cnf, restart the service after the settings are completed, check the status through SHOWSTATUS, reasonably adjust the timeout time and monitor the plug-in operation.
    Mysql Tutorial . Database 255 2025-07-15 02:35:40
  • Exploring Window Functions Available in MySQL 8
    Exploring Window Functions Available in MySQL 8
    MySQL8.0 introduces window functions to improve SQL analysis capabilities. 1. RANK and ROW_NUMBER are used for rankings. The former handles the sorting rankings, and the latter forces unique numbers; 2. SUM and AVG support rolling calculations to achieve cumulative and moving averages; 3. FIRST_VALUE and LAST_VALUE extract window head and tail data, and the default range needs to be adjusted to obtain complete results. These functions retain the original row structure and simplify complex queries.
    Mysql Tutorial . Database 215 2025-07-15 02:32:30
  • mysql alter table add column
    mysql alter table add column
    The most common way to add new columns in MySQL is to use the ALTERTABLE...ADDCOLUMN statement. The basic syntax is: ALTERTABLE table name ADDCOLUMN new column name data type [constraint condition][position]; for example ALTERTABLEusersADDCOLUMNphoneVARCHAR(20); you can specify the location such as AFTERusername; add non-empty fields to set the default value, such as ALTERTABLEusersADDCOLUMNstatusTINYINTNOTNULLDEFAULT1; performance issues should be paid attention to when operating large data tables, and it is recommended to execute or use online D during low peak periods.
    Mysql Tutorial . Database 901 2025-07-15 02:27:31
  • Choosing appropriate data types for columns in MySQL tables
    Choosing appropriate data types for columns in MySQL tables
    WhensettingupMySQLtables,choosingtherightdatatypesiscrucialforefficiencyandscalability.1)Understandthedataeachcolumnwillstore—numbers,text,dates,orflags—andchooseaccordingly.2)UseCHARforfixed-lengthdatalikecountrycodesandVARCHARforvariable-lengthdata
    Mysql Tutorial . Database 873 2025-07-15 02:25:50
  • what is a mysql trigger
    what is a mysql trigger
    The actual function of MySQL trigger is to automatically perform additional operations when data changes, such as generating default settings, recording logs, data backup, etc. For example, when updating the order status, the old status will be automatically recorded in the log table. The basic types of triggers are divided into BEFORE triggers (for verification or preprocessing) and AFTER triggers (for logging or subsequent processing). Each type can correspond to three operations: INSERT, UPDATE, and DELETE, and a total of 6 combinations are formed, such as BEFOREINSERT, AFTERUPDATE, etc. The syntax for creating triggers includes defining the name, point in time, operation type, association table and specific SQL statements, such as automatically writing statistics tables when inserting new employees. Notes required to use triggers
    Mysql Tutorial . Database 923 2025-07-15 02:21:00

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