The September 2021 DB‑Engines ranking shows Oracle, MySQL and SQL Server plummeting while MongoDB, Snowflake and ClickHouse surge, highlighting a shift toward niche and cloud‑native databases, and the article also recommends ten essential database books for professionals.
This article details NetEase Games’ evolution of its Flink SQL platform, from the early StreamflySQL v1 template‑JAR approach to the v2 SQL‑Gateway architecture, discussing design decisions, challenges such as metadata persistence, multi‑tenant security, horizontal scaling, and job state management.
This article compares Elasticsearch and ClickHouse in terms of architecture, query capabilities, and performance for log analytics, presenting test setups, Docker‑compose configurations, query examples, and benchmark results that show ClickHouse generally outperforms Elasticsearch in most basic query scenarios.
The September 2021 DB‑Engines ranking shows major declines for Oracle, MySQL and SQL Server, rapid gains for Snowflake and MongoDB, and highlights emerging time‑series and key‑value databases like InfluxDB, Redis, and ClickHouse reshaping the database market.
The article explains ClickHouse's new Projection feature, how it overcomes MergeTree's single‑sort limitation and materialized view drawbacks, provides step‑by‑step commands to create, materialize, and query projections, demonstrates massive performance gains, and outlines the rules for automatic projection selection.
This article provides a comprehensive guide to Flink Table and SQL window semantics—including group, tumbling, sliding, and session windows—covers over windows, demonstrates how to define windows in SQL, explains built‑in functions, shows how to implement scalar, table, aggregate and table‑aggregate UDFs, and details Flink's integration with Hive, complete with Maven dependencies and runnable examples.
This article explains why duplicate rows appeared in production MySQL tables, demonstrates how to identify them with SELECT queries, and provides two SQL solutions—one to delete all duplicates and another to keep a single record per duplicated key—while preserving data integrity.
This guide explains how LEFT JOIN creates a temporary result set, compares the effects of applying a WHERE filter after the join versus embedding the condition in the ON clause, and shows practical SQL examples with sample tables and result analysis.
This article provides a comprehensive guide to Apache Flink's Table API and SQL, covering required dependencies, the differences between old and Blink planners, program structure, table environment creation, catalog registration, query execution, conversion between DataStream and Table, update modes, and time attribute handling, with Scala code examples throughout.
This guide explains how multi‑index support in Table Store enables SQL push‑down of filters, relational operators, aggregation functions, and LIMIT clauses, dramatically reducing query latency on non‑primary‑key columns and providing practical examples with a bike‑rental dataset.
This article explains the impact of slow SQL on database resources and user experience, outlines priority rules for addressing slow queries, details MySQL execution steps, identifies key performance factors, and provides concrete optimization methods including enabling slow‑query logs, indexing, I/O merging, and distributed architecture.
This article examines how Oracle, PostgreSQL, and MySQL implement and use database sequences for primary keys, covering explicit calls, trigger‑based, DEFAULT, and AUTO_INCREMENT methods, version support, and the effects of INSERT, UPDATE, DELETE, and TRUNCATE operations, concluding with a comparative summary.
This comprehensive guide covers essential SQL concepts, clause usage, aggregate functions, view creation, sequences, indexes, and a collection of classic interview questions with detailed solutions, helping readers deepen their database knowledge and ace SQL interviews.
This article explains why mastering SQL and PostgreSQL is essential for data scientists, outlines the core skills of the role, describes PostgreSQL’s features, lists its advantages and drawbacks for data science, and suggests resources for getting started.
This article explores TiDB performance optimization by examining layered approaches—hardware, software, and SQL—and scenario‑specific tactics such as read/write hotspot handling, OLAP challenges, and distributed transaction tuning, offering practical insights and real‑world case studies from industry experts.
This article provides a thorough introduction to MyBatis, including a complete beginner example with database schema, Maven configuration, XML and Java mapper files, and a demo program, followed by an in‑depth explanation of MyBatis’s lifecycle, core components such as SqlSession, Executor, StatementHandler, ParameterHandler, ResultSetHandler, and their interactions.
The article presents a step‑by‑step MyBatis tutorial that creates a sample user table, adds Maven dependencies, configures MyBatis, defines mapper XML and Java interfaces, demonstrates a test program, and explains core components such as SqlSession, Executor, StatementHandler, ParameterHandler, and ResultSetHandler.
Geohash encodes latitude‑longitude pairs into short base‑32 strings by recursively bisecting coordinate ranges and interleaving bits, allowing fast proximity queries via prefix matching, with precision controlled by string length, and is supported natively in Redis and useful for location‑based services.
This article explains the purpose and interpretation of each column in MySQL's EXPLAIN output, covering identifiers, select types, table sources, partition info, access types, possible keys, actual keys, key lengths, row estimates, filtering percentages, and extra execution details, with visual examples and code snippets.
The article explains why TiDB discourages large transactions, outlines the historical transaction limits, shows how to configure size thresholds, and provides concrete scripts for splitting big updates based on primary‑key characteristics to keep transaction size within safe bounds.
This article reviews the evolution of big data technologies in the last five years, covering streaming and batch processing frameworks, column‑store NoSQL databases, programming language trends, the cloud‑native multi‑model database Lindorm, and practical Flink/Blink usage with code examples.
This article introduces the six fundamental parts of Structured Query Language (SQL)—DQL, DML, TPL, DCL, DDL, and CCL—while promoting a comprehensive Alibaba Cloud developer course that covers each component with detailed lessons and practical examples.
This article compiles a comprehensive set of MySQL interview questions covering index types, the differences between MyISAM and InnoDB, the rationale for auto‑increment primary keys, sharding strategies, ACID properties, isolation levels, storage‑engine trade‑offs, normalization, index best practices, data types, performance tuning, locking mechanisms, B+Tree characteristics, and common SQL operations.
This article presents a detailed performance benchmark comparing MariaDB 10.4.12 and MySQL 8.0.19 on an i7 Windows 10 system, covering single and batch inserts, indexed and non-indexed queries, and analyzes speed and memory usage differences between the two databases.
This guide introduces DBeaver, a free open‑source database management tool, covering its cross‑platform installation, how to create and configure database connections (including JDBC driver handling), and the steps to generate entity‑relationship diagrams from existing databases.
This article explains why MySQL uses locks, describes table‑level, row‑level, and page‑level locking, outlines lock types such as shared, exclusive, and intention locks, and provides practical usage examples and common troubleshooting tips for InnoDB and other storage engines.
This article demonstrates how Fluent Mybatis can build complex SQL without XML, compares its implementation with native Mybatis and Mybatis‑Plus for a student score statistics query, and reviews code‑generation settings and feature overviews to help developers choose the most efficient data‑access framework.
This article presents a complete MySQL interview guide, including a script to create and populate tables for students, teachers, courses, scores, and grades, followed by 33 common interview questions with detailed SQL solutions covering selection, aggregation, joins, subqueries, and ordering.
Using MySQL's ORDER BY with LIMIT can yield an unexpected row order because duplicate values in the sorting column cause nondeterministic results; adding a unique secondary column like id stabilizes the order, and the official documentation explains how LIMIT influences query planning and optimization.
This article introduces ClickHouse, a high‑performance open‑source columnar database, explains its architecture versus row‑based systems, details migration from MySQL, showcases installation, performance benchmarks, data‑sync strategies, common pitfalls, and summarizes its benefits for large‑scale analytical workloads.
This article explains several MySQL techniques—INSERT IGNORE, ON DUPLICATE KEY UPDATE, INSERT…SELECT WHERE NOT EXISTS, and REPLACE—plus a practical MyBatis batch‑insert example, to handle large‑scale data imports while preventing duplicate records.
This article introduces ClickHouse as a column‑oriented OLAP database, compares it with traditional row‑based databases, and details a real‑world migration from MySQL that reduced query time from minutes to under one second, along with performance testing, sync strategies, and common pitfalls.
The article examines a real‑world scenario where a developer tried to reuse existing stored procedures to merely check the presence of Job, Certification, and Disclosure records, discusses the pitfalls of such an approach, and explains why storing this logic in T‑SQL is often fragile and hard to maintain.
This whitepaper explains the concept of in‑memory databases, traces their historical development, outlines core attributes and typical use cases in e‑commerce, live streaming and telecom, compares leading products, and provides technical and management recommendations for hardware and product selection as well as future trends.
This article explains how to retrieve sales statistics for multiple business units and their associated products from a MySQL table, compares several implementation approaches—including loop queries, OR concatenation, mixed filtering, and row‑comparison using MyBatis dynamic SQL—evaluates index usage, and provides the final recommended solution.
During a performance test a MySQL server showed one CPU core constantly at 99% while the others were idle, prompting a detailed investigation that checks I/O thread settings, multi‑core utilization, transaction locks, slow‑query logging, and index optimization to resolve the bottleneck.
This comprehensive guide covers fundamental SQL concepts, syntax, and terminology, then walks through CRUD operations, subqueries, joins, unions, functions, ordering, grouping, data definition, transaction control, permission management, stored procedures, cursors, and triggers, providing clear examples for each.
The article explains the drawbacks of strict relational normalization, introduces the concept of anti‑normalization (controlled redundancy) to simplify queries, demonstrates it with a set of employee, department, salary tables and four typical query scenarios, and shows how denormalizing the schema can dramatically improve MySQL query performance.
This guide walks you through installing DataGrip, configuring connections and drivers, using its powerful SQL editor, navigating objects, exporting and importing data, and leveraging advanced shortcuts and features to streamline database development and management.
MySQL 8.0 introduces several relational‑database enhancements, including invisible indexes for performance tuning, persistent configuration via SET PERSIST, default utf8mb4 character set, support for Common Table Expressions, and window functions, each illustrated with practical SQL examples.
The article describes how to design a MySQL table for product sales statistics, initialize large data sets, and compare several approaches—including loop queries, OR concatenation, mixed filtering, and row‑comparison techniques—ultimately selecting row‑comparison as the most efficient solution within MyBatis dynamic SQL constraints.
This article provides a comprehensive overview of data warehouse concepts, compares classic warehouse models, explains dimensional modeling fundamentals such as fact and dimension tables, demonstrates a practical e‑commerce scenario with schema design and SQL query examples, and discusses real‑world trade‑offs.
When a MySQL query uses LIMIT with a large offset on a table of millions of rows, the database must scan hundreds of thousands of index entries and corresponding clustered rows, causing massive random I/O; rewriting the query with a sub‑query join reduces I/O dramatically, cutting execution time from over a minute to under a second while also preventing buffer‑pool pollution.
This article demonstrates how to use Fluent MyBatis, native MyBatis, and MyBatis‑Plus to query a student_score table for term‑wise statistics of English, Math, and Chinese scores, providing complete code examples, SQL statements, mapper definitions, and code‑generation configurations for each approach.
This guide explains step‑by‑step how to identify and delete duplicate records in MySQL tables, covering simple SELECT checks, handling MySQL’s update‑from limitation, and fast deletion techniques that keep one record per duplicate group.
This article offers a thorough overview of relational database fundamentals and SQL syntax, detailing core concepts, clause structures, DDL/DML/TCL/DCL commands, functions, transaction handling, user privileges, stored procedures, cursors, and triggers with practical code examples.
This article explains why a naïve Python script for deleting duplicate MySQL rows is too slow, demonstrates the MySQL error caused by deleting from the same table you query, and provides two pure‑SQL solutions: one that removes all duplicates and another that keeps a single row per duplicate key.
This article benchmarks MySQL's datetime, timestamp, and bigint columns by inserting 500,000 rows and measuring query, group‑by, and order‑by performance, concluding that bigint generally offers the best speed for time‑based operations while timestamp saves space for static timestamps.
This article explains how MySQL treats NULL values, the operators and functions for handling them, demonstrates that IS NULL can still use indexes, shows the impact on aggregate functions, distinct, group by and order by, and recommends defining columns NOT NULL to avoid performance pitfalls.
This article examines the requirements of commercial advertising systems for data storage, traces the evolution from single‑node MySQL to BaikalDB’s cloud‑native, MySQL‑compatible distributed architecture, and details its storage, compute, and scheduling designs, highlighting key features such as Raft replication, RocksDB storage, and hybrid OLTP/OLAP support.
This article explains how PolarDB‑X classifies different data‑deletion scenarios, compares traditional recovery methods like PITR, Flashback Query, and binlog‑based tools, and introduces its precise SQL‑level flashback feature that uses TraceID to quickly and accurately restore mistakenly deleted rows.
The article presents a detailed interview‑style walkthrough of MySQL InnoDB locking mechanisms, covering table‑ versus row‑level locks, shared and exclusive locks, intention locks, gap and next‑key locks, auto‑increment locks, predicate locks, and related SQL statements, illustrated with tables and code examples.
This article explains how Vipshop built the Hera data service since 2019 to provide a unified API for warehouse access, detailing its background, architecture, core features such as multi‑engine queries, adaptive execution, custom Lisp syntax, task scheduling, metrics collection, and performance gains for both B‑to‑B and B‑to‑C workloads.
This article analyzes MySQL 8.0.25 source code, detailing the server architecture, parser reconstruction, prepare/rewrite stages, the optimizer transformations, and the new hypergraph optimizer, while also comparing these mechanisms with PostgreSQL’s processing pipeline.
This article provides a detailed tutorial on relational database fundamentals, covering key terminology, SQL syntax, DDL/DML/DCL/TCL commands, query clauses, joins, set operations, functions, aggregation, indexing, constraints, transactions, permission management, stored procedures, cursors, and triggers with practical code examples.
This article compiles extensive interview questions and topics covering Hadoop, Spark, Flink, Hive, Kafka, MySQL, Redis, Java fundamentals, and algorithms, organized by companies such as Xiaomi, ByteDance, Alibaba, Shopee, Tencent, Meituan, NetEase, and Baidu, to help candidates prepare effectively for big‑data engineering roles.
This article explains why MySQL's auto‑increment counter can be lost after a server restart for InnoDB tables, compares the behavior with MyISAM, demonstrates the problem with practical SQL examples, and shows how MySQL 8.0 fixes the counter logic.
This article explains several MySQL techniques—INSERT IGNORE, ON DUPLICATE KEY UPDATE, and REPLACE INTO—to efficiently insert large volumes of data while preventing duplicate primary‑key or unique‑key rows, and provides practical code examples for single and batch operations.
This article details the practical challenges encountered when migrating a MariaDB 10.3 database to MySQL 5.7.25, explains why certain defaults and engine-specific options cause import errors, and provides step‑by‑step fixes such as adjusting default expressions, removing Aria‑specific parameters, and configuring sql_mode.
This article explains MySQL's three‑layer logical architecture, the end‑to‑end query execution flow, and the inner workings of the optimizer, cache, and storage engine, then offers practical schema, index, and specific‑query tuning techniques to boost database performance.
This article provides a comprehensive collection of MySQL command-line instructions for exporting databases or tables, importing data, managing databases and tables, performing DDL and DML operations, handling field types, and configuring user privileges, all illustrated with practical code examples.
This article explains why a naïve Python script for deduplicating millions of rows is too slow, then walks through a series of MySQL queries—including how to identify duplicate names, avoid the 1093 error, and delete duplicates while keeping a single representative row—demonstrating fast, reliable cleanup of large tables.
This article provides a comprehensive collection of MySQL optimization techniques—including storage engine characteristics, data type selection, index design, and query rewriting—targeted at teams without a dedicated DBA, using MySQL 5.5 and InnoDB as the reference platform.
Flyway is an open‑source database migration tool that version‑controls SQL scripts, supports many databases, and integrates with Maven and Spring to automate schema changes across environments, offering commands such as migrate, clean, info, validate, baseline, undo and repair, with detailed configuration examples.
This article investigates the meaning of the number in parentheses for MySQL INT types, demonstrates through storage tests that INT(4) and INT(11) have identical storage size and range, and explains how the ZEROFILL attribute changes only the displayed width.
This tutorial walks data analysts through setting up a Python environment with Jupyter and Anaconda, importing diverse datasets via Pandas, cleaning and reshaping data, performing calculations, filtering, visualizing results, and finally merging and grouping data to produce insightful analyses comparable to SQL and Excel workflows.
This article explains how to identify and delete duplicate records in large MySQL tables, discusses why a naïve delete fails, and provides two robust SQL solutions—one that removes all duplicates and another that retains a single row per duplicated key—demonstrating fast execution even on tables with hundreds of thousands of rows.
This comprehensive guide covers SQL fundamentals—including database terminology, syntax structure, DDL/DML/TCL/DCL commands, CRUD operations, subqueries, joins, unions, functions, ordering, grouping, indexes, constraints, transactions, permissions, stored procedures, cursors, and triggers—providing clear examples and best practices for relational database development.
This article compiles 100 common MySQL interview questions for developers, covering index structures and optimization, transaction ACID properties and isolation levels, primary‑key design, storage‑engine choices, sharding strategies, and miscellaneous SQL nuances such as binlog formats and MyBatis parameter handling.
This article summarizes comprehensive MySQL index design guidelines, covering naming conventions, column selection criteria, index count control, handling of frequently updated columns, function and duplicate indexes, small‑table considerations, and index ordering to optimize query performance.
This article describes how to identify and delete duplicate rows in MySQL tables—first showing a naive Python‑based approach, then presenting efficient SQL queries that locate duplicate names, explain MySQL's limitation on deleting from the same table being queried, and provide a safe sub‑query solution to remove all duplicates while preserving a single representative row.
This article explains MySQL's SQL Mode concept, lists the default mode values for MySQL 5.7, demonstrates how to view and change the mode with SQL commands, describes the impact of common modes such as STRICT_TRANS_TABLES and ONLY_FULL_GROUP_BY, and provides a complete reference table of all supported mode values and predefined mode combinations.
This article demonstrates how to use the RETURNING clause in Tencent Cloud Enterprise MySQL to retrieve inserted, replaced, or deleted rows directly, showing step‑by‑step examples with images and explaining the behavior of RETURNING, REPLACE RETURNING, and DELETE RETURNING statements.
This article provides a comprehensive collection of 52 practical tips for improving SQL query performance, covering index creation, query rewriting, data type selection, storage engine choices, and execution plan analysis to help developers write faster, more efficient database statements.
This article explains how data-driven decision making evolves from simple Excel and Python analysis to robust data warehouses, introduces star‑schema dimension modeling, and demonstrates practical integration of Alibaba Cloud MaxCompute with Tableau for interactive OLAP‑style analytics.
This article examines a real‑world Oracle SQL query, identifies costly full‑table scans and low‑selectivity columns, and demonstrates how creating an index on a key column reduces execution time from 24 minutes to just one second, highlighting essential SQL performance‑tuning techniques.
This article explains MySQL’s logical architecture, query processing steps, and the principles behind query optimization, covering topics such as client‑server protocol, query cache, parsing, cost‑based optimizer, execution engine, and practical index design strategies to improve performance.
Developers often use SELECT count(*) to check record existence, but replacing it with SELECT 1 … LIMIT 1 improves performance by stopping after the first match, allowing simpler Java null checks and potentially reducing index usage, especially when only a binary presence test is needed.
This article compares Elasticsearch and ClickHouse for log analytics, detailing their architectures, node roles, query capabilities, and performance through Docker‑Compose stacks and synthetic syslog data, concluding that ClickHouse generally outperforms Elasticsearch in speed and aggregation efficiency.
This tutorial explains how to import the built‑in sqlite3 library in Python, create and connect to a SQLite database file, define tables, insert and query records, and seamlessly exchange data with Pandas data frames, while also showing how to access the database via SQL client tools.
The article explains why using COUNT(*) for existence checks is inefficient and demonstrates a more performant approach by selecting a constant with LIMIT 1, providing Java examples and showing how this reduces database work and improves query speed.
This article explores how backend developers can handle intricate e‑commerce search filters by first attempting a monolithic SQL solution, then improving performance with index analysis and query splitting, and finally achieving fast, scalable results using Redis sets, sorted sets, and transaction commands.
ClickHouse is an MPP column‑oriented DBMS that combines full DBMS functionality, advanced columnar storage with high compression, SIMD‑based vectorized execution, a rich relational SQL interface, diverse table engines, multi‑master clustering, and flexible sharding and distributed query capabilities, making it exceptionally fast for analytical workloads.
This article compares ClickHouse and Elasticsearch for API log storage, detailing development activity, schema handling, query performance, statistical functions, MySQL integration, new features, and practical drawbacks, while providing concrete SQL examples and migration tips.
The article introduces the command‑line utility q, explains how to install it on Linux and Windows, and demonstrates using familiar SQLite‑style SQL queries to search, filter, join, and aggregate log files and command output, offering a convenient alternative to traditional shell tools.
This tutorial walks through MySQL join techniques—including WHERE, LEFT, and INNER joins—shows how to retrieve specific columns, and provides clear examples of inserting single or multiple rows, updating records, and deleting data, all illustrated with step‑by‑step SQL code and result screenshots.
This article walks you through using Navicat for MySQL to create databases and tables, design table structures, and perform native SQL SELECT queries—including filtering, multiple conditions, and column selection—illustrated with step‑by‑step screenshots and code examples.
The article explains why a simple GROUP BY query in MySQL 5.6 returns the earliest rows instead of the most recent ones, demonstrates how to correctly obtain the latest record per name using sub‑queries or window functions, and discusses the impact of the ONLY_FULL_GROUP_BY mode in MySQL 5.7.
MySQL deep pagination can be dramatically accelerated by ordering on the primary key, indexing the sort column, and using keyset pagination or a sub‑query join instead of scanning millions of rows, while only minor tweaks like increasing sort_buffer_size provide negligible gains.
This article explains how MySQL may rewrite a LEFT JOIN as an INNER JOIN during optimization when the WHERE clause filters the joined table, demonstrates the behavior with sample class and student tables, and presents test cases confirming the optimizer's decision.
This article investigates why MySQL queries with large LIMIT offsets become extremely slow, demonstrates the issue with simulated millions‑of‑row datasets, and presents three optimization strategies—including index‑covering subqueries, remembering the last primary‑key position, and applying offset throttling—to achieve consistent, fast pagination performance.
This article walks through a practical MySQL tutorial that identifies duplicate records, explains why naïve row‑by‑row deletion is slow, and provides efficient DELETE statements—including derived‑table tricks—to clean up large tables while preserving one record per duplicate group.
This article provides a comprehensive overview of Apache Flink SQL 1.13, detailing new Window TVF support, cumulate windows, performance optimizations, time‑zone handling, enhanced Hive compatibility, SQL client upgrades, DataStream‑Table conversion improvements, and outlines the roadmap for the upcoming 1.14 release.
This article explains how to detect table‑space fragmentation in MySQL, demonstrates the performance impact of deleted rows, and provides step‑by‑step commands—including ALTER TABLE FORCE, OPTIMIZE TABLE, and mysqlcheck—to reclaim space and improve query speed.
The article recounts a recent project where reusing existing stored procedures to check a user's Job, Certification, and Disclosure data led to maintenance headaches, prompting a discussion of alternative approaches, their drawbacks, and why duplicating the query sometimes becomes the only viable solution.
SQLFlow is an open‑source platform that lets users build and run machine‑learning and deep‑learning models directly from SQL statements, lowering the barrier for business analysts to apply AI by abstracting complex pipelines into familiar database queries.
This article provides a comprehensive overview of ClickHouse, covering its columnar OLAP architecture, key features such as data compression, vectorized processing, distributed query handling, and SQL support, followed by detailed step‑by‑step instructions for deploying a multi‑node ClickHouse cluster with MergeTree and ReplicatedMergeTree engines, configuration files, and Java MyBatis integration.
This article introduces the command‑line utility q, explains how to install it on Linux and Windows, and demonstrates using full SQLite‑compatible SQL syntax to query, filter, join, and aggregate plain‑text log files, offering a database‑style alternative to traditional shell tools.
This guide walks you through installing DataGrip, configuring drivers, connecting to various databases, using its powerful SQL editor with shortcuts, customizing appearance, performing data export/import, and leveraging advanced navigation and editing features to boost productivity.
This article explains why correlated subqueries are a performance bottleneck, introduces the Apply (Correlated Join) operator, classifies subquery types, shows how to transform them into efficient joins, and discusses rule‑based push‑down techniques for Project, Filter, Aggregate, and Set operations.
