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Home

Technical Articles

Database

Mysql Tutorial

How to use the ON DUPLICATE KEY UPDATE statement in MySQL

ONDUPLICATEKEYUPDATE is used in MySQL to handle unique key conflicts. 1. When there is a primary key or unique constraint conflict in the insert row, an update is performed instead of an error is reported; 2. Use VALUES (column) to refer to the insert value, and can update specific fields in combination with expressions; 3. Applicable to counters, upsert operations and batch data import; 4. Only trigger unique key conflicts, and updates each row at most once; 5. Different from INSERTIGNORE (ignore) and REPLACE (delete and insert), it is more efficient and safe; 6. It is necessary to ensure that the table has a correct unique index, and pay attention to the self-increment field behavior; this mechanism reduces database round trips and improves performance.

Aug 12, 2025 pm 04:04 PM

How to use aggregate functions in MySQL?

The aggregation function in MySQL is used to calculate the data and return a single value, often used in conjunction with the GROUPBY clause to summarize the data. 1. The COUNT() function can count row counts. COUNT(*) contains NULL values. COUNT(column name) only counts non-NULL values; 2. SUM() and AVG() respectively calculate the sum and average of the numeric columns, and can control the decimal places in combination with the ROUND() function; 3. MAX() and MIN() return the maximum and minimum values, which are suitable for numerical, date and other types; 4. Use GROUPBY to group by specified columns, and apply aggregate functions to each group to implement classification statistics; 5. Use the HAVING clause to filter the results after grouping, and WHERE is used for row filtering before grouping

Aug 12, 2025 pm 04:01 PM

mysql aggregate function

How to use the IN operator in MySQL?

TheINoperatorinMySQLchecksifavaluematchesanyinaspecifiedlist,simplifyingmultipleORconditions;itworkswithliterals,strings,dates,andsubqueries,improvesqueryreadability,performswellonindexedcolumns,supportsNOTIN(withcautionforNULLs),andcanbecombinedwith

Aug 12, 2025 pm 03:46 PM

mysql IN操作符

Designing MySQL Databases for Billing and Subscription Services

When designing MySQL databases for billing and subscription services, the core goal is to ensure data accuracy, scalability, and query efficiency. 1. Use the intermediate table user_subscriptions to manage many-to-many relationships between users and subscription plans, and support history; 2. Bills record each deduction information, and indexes are established according to user_id and due_date for easy query; 3. Payment records separate table payments, supporting multiple payment methods and refund processing; 4. Automatically update subscription status through timed tasks, generate bills and trigger notifications; 5. Reasonably design index and table structure to improve performance and maintenance. Good database design helps the system stay stable and efficient when user growth and function expansion

Aug 12, 2025 pm 03:00 PM

How to use MySQL partitioning to manage large tables?

MySQL partitions can improve the performance and management of large tables. The key is to select the appropriate type and match the query mode: 1. Select RANGE (by time range), LIST (discrete value grouping), HASH (even distribution) or KEY (support non-integer columns) partitions according to the data characteristics; 2. Design partitions need to be around query mode to ensure that WHERE conditions include partition columns to achieve partition cropping; 3. Verify the cropping effect through EXPLAINPARTITIONS to avoid unnecessary sub-partitions; 4. Regularly manage the life cycle, such as adding new partitions in advance, quickly deleting old partitions, reorganizing future partitions, and automating with events or scripts; 5. Comply with restrictions and best practices, such as the unique key must contain partition columns, and InnoDB supports partitions

Aug 12, 2025 pm 02:57 PM

How to select random rows from a table in MySQL

To select random rows from MySQL table, the most common method is to use ORDERBYRAND(); the specific steps are: 1. Use SELECTFROMtable_nameORDERBYRAND()LIMITN to obtain N random records; 2. Note that this method has poor performance on large tables, because the full table needs to be scanned and sorted; 3. For large tables, you can use random offset SELECTFROMtable_nameLIMIT1OFFSETFLOOR(RAND()(SELECTCOUNT()FROMtable_name)); 4. If there is an ID gap, you can use SELECTFROMtable_nameWHEREid

Aug 12, 2025 pm 02:52 PM

How to handle time-series data effectively in MySQL?

To effectively process time series data in MySQL, schema design, indexing and query need to be optimized. The specific methods are: 1. Use DATETIME(6) or TIMESTAMP(6) to store timestamps to support microsecond accuracy and facilitate date calculation, avoid using integer timestamps; 2. Create composite indexes (such as sensor_id, timestamp) for time range and entity queries, and partition by time (such as one partition per month) to improve query efficiency and deletion speed; 3. Use batch insertion and transactions to reduce overhead when writing, and only select necessary fields when reading, use indexes and pre-aggregate data (such as maintaining hourly summary tables) to accelerate analysis; 4. Use efficient data retention through partition deletion or batch deletion to avoid large-scale DE

Aug 12, 2025 pm 02:49 PM

What is the purpose of an index in MySQL?

ThepurposeofanindexinMySQListoimprovequeryperformancebyenablingfasterdataretrieval.1)IndexesallowMySQLtoquicklylocaterowsusingafastlookupmechanism,avoidingfulltablescans.2)TheyspeedupsearchesinWHEREclauses,especiallyonfrequentlyqueriedcolumnslikeemai

Aug 12, 2025 pm 02:29 PM

mysql index

How to concatenate strings in MySQL

When using CONCAT(), if any parameter is NULL, the result is NULL, and it needs to be processed with IFNULL() or COALESCE(); use CONCAT_WS() to automatically ignore the NULL value and connect the string with the specified delimiter; 1. Use CONCAT() when it is determined that there is no NULL value or NULL needs to be explicitly processed; 2. Use CONCAT_WS() when you need a delimiter and want to skip the NULL value; 3. Combining IFNULL() or COALESCE() in CONCAT() can avoid the problem that NULL results in NULL, and you should select a suitable function based on whether NULL may contain NULL and whether a delimiter is required.

Aug 12, 2025 pm 02:23 PM

How to drop an index in MySQL

UseDROPINDEXindex_nameONtable_nameforregularanduniqueindexes.2.UseALTERTABLEtable_nameDROPINDEXindex_nameasanalternativesyntax.3.UseALTERTABLEtable_nameDROPPRIMARYKEYtoremoveaprimarykey,notingthatforeignkeyconstraintsmustberemovedfirstifpresent.4.For

Aug 12, 2025 pm 02:03 PM

How to optimize queries in MySQL

UseproperindexingbyaddingindexesoncolumnsinWHERE,JOIN,ORDERBY,andGROUPBYclauses,usingcompositeindexesformultiple-columnfilters,avoidingover-indexing,andremovingunusedindexes.2.WriteefficientqueriesbyselectingonlyneededcolumnsinsteadofusingSELECT*,avo

Aug 12, 2025 pm 01:58 PM

mysql Query optimization

How to use the JSON_ARRAY function in MySQL

The JSON_ARRAY() function is used to create JSON arrays. 1. You can pass in strings, numbers, NULL or JSON values to generate an array, such as JSON_ARRAY('apple','banana') returns ["apple","banana"]; 2. You can combine table columns to generate JSON arrays for each row, such as SELECTJSON_ARRAY(id, name, price)FROMproducts; 3. Support nested structures and can contain other JSON arrays or objects; 4. When any parameter is NULL, the result is displayed as null, and when there is no parameter, the empty array is returned []; this function is applicable

Aug 12, 2025 pm 01:54 PM

MySQL Database Performance Tuning for Complex Queries

Optimizing complex queries requires many aspects to start. 1. Use EXPLAIN to analyze the execution plan and see if the full table is scanned or temporary tables are used; 2. Design the index reasonably, combine indexes are better than single column indexes to avoid leading column mismatch, over-index and low-distinguishing fields; 3. Reduce data processing, avoid SELECT*, split large queries, and control the number of JOINs; 4. Adjust configuration parameters such as sort_buffer_size, join_buffer_size, and innodb_buffer_pool_size, but be cautiously verified.

Aug 12, 2025 am 10:56 AM

How to configure MySQL for UTF-8 support completely

To implement the full UTF-8 support of MySQL, you must use utf8mb4 and ensure that all levels of configuration are consistent. 1. Use utf8mb4 instead of utf8 because it supports 4-byte Unicode characters (such as emoji); 2. Configure the default character set of client, mysql and mysqld segments in my.cnf to utf8mb4, and enable the innodb_large_prefix and Barracuda file formats; 3. Convert existing databases, tables and columns to utf8mb4 through the ALTERDATABASE, ALTERTABLE and MODIFY commands; 4. Set the character set when applying connections, such as using PD in PHP;

Aug 12, 2025 am 09:48 AM