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1. Concept: Java database connectivity, Java database connection, Java language operation database JDBC essence: it is actually a set of rules defined by the official (sun company) to operate all relational databases, that is, interfaces. Each database manufacturer implements this interface and provides database driver jar package. We can use ...

background MySQL has become the first choice for most companies with low-cost and rich Internet resources. Although the performance is excellent, how to better use the so-called "good horse with good saddle" has become a compulsory course for development engineers. We often see requirements such as "proficient in MySQL", &q ...

Slow query and slow log Query and start of slow log Query whether the slow log is enabled mysql> show variables like 'slow_query_log'; +----------------+-------+ | Variable_name | Value | +----------------+-------+ | slow_query_log | OFF | +----------------+-------+ 1 row in set (0.00 sec) Enable slow query log # It is convenien ...

1, Meaning of subquery Meaning: select statements that appear in other statements are called subqueries or intra queries; The external query statement is called primary query or external query Classification: According to the location of sub query: After select: only scalar subqueries are supported After from: only table subqueries are ...

preface The ECS that Alibaba cloud bought for 95 yuan is about to expire. It needs more than 1000 to renew. I thought there was nothing important on the server, so I took advantage of Tencent cloud discount and spent 288 to buy a three-year CVM. CVM is a cloud virtual machine. Let's call it a server for the time being. 1 core 2G, it seems tha ...

catalogue 12.1MySQL configuration file (1) Configuration section (2) Basic configuration (3) Memory and optimized configuration (4) Log configuration 12.2 data backup and restore (1) Data backup (2) Data restore (3) Binary log 12.3 multi instance deployment 12.4 master slave replication 12.1MySQL configuration file (1) Configu ...

Connection query (this article only introduces the connection query of SQL 92 standard in detail) 1, Meaning and classification of connection query meaning: Also known as multi table query, join query will be used when the query fields come from multiple tables Cartesian product phenomenon: Suppose that table 1 has m rows, table 2 has n ...

Database structure diagram 1. Retrieve data 1.1 select database USE sql5th; 1.2 select a single column select prod_name from Products; +---------------------+ | prod_name | +---------------------+ | Fish bean bag toy | | Bird bean bag toy | | Rabbit bean bag toy | | 8 inch teddy bear | | 12 inch teddy bear | | ...

1 Overview 1.1 what are the sub warehouse and sub table Xiao Ming is a developer of a start-up e-commerce platform. He is responsible for the function development of the seller module, The related businesses of shops and commodities are involved, and the design is as follows Database: Store information and geographical area inform ...

– one Prepare data Four tables are known as follows: Student form: student (student number, student name, date of birth, gender) Transcript: score (student number, course number, grade) Course schedule: Course (course number, course name, teacher number) Teacher form: teacher (teacher number, teacher name) Write the corresponding SQL sta ...