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Execution of a SQL statement

The MySQL driver helps us connect to the database at the bottom level. Only after the connection is established can subsequent interactions be possible. Using a connection pool greatly saves the overhead of constantly creating and destroying threads. This is the famous "pooling" idea, which can be seen in both thread pools and HTTP connection pools.

Feb 17, 2021 am 10:32 AM

SQL

Introduction to database sql view

View introduction A view (View) is a virtual table that is basically transparent to users who use the view. The view does not actually exist in the database. The row and column data come from the tables used in the query of the custom view and are dynamically generated when the view is used. Define the view create view view name as select statement SELECT * FROM provinces;CREATE VIEW v_pro AS SELECT * FROM provinces;SELECT * FROM v_pro; View view When viewing the table, the view table will also be listed show table

Feb 04, 2021 am 07:58 AM

sql视图

Does the sql statement between include boundary values?

In SQL Server, the SQL statement "between and" includes boundary values, and "not between" does not include boundary values. The "BETWEEN ... AND" statement selects a range of data between two values; these values can be numeric, text, or dates.

Feb 03, 2021 pm 04:38 PM

sql语句between

shock! There are so many locks in one SQL statement...

The concept of gap lock is indeed a bit difficult to understand, especially after working with uplink lock, it is easy to make mistakes in judging whether lock waiting will occur. So today, let’s start with this locking rule. First of all, let me explain that I have not seen a similar summary of these locking rules elsewhere. In the past, when I made my own judgments, I always thought about the implementation in the code. This time, in order to summarize the rules into rules that students who don’t read the code can understand, I re-brushed the code and temporarily summarized it.

Feb 02, 2021 pm 05:53 PM

SQL锁

Learn about SQL injection and how to fix it

SQL injection means that the web application does not judge the legality of the user input data or does not filter it strictly. The attacker can add additional SQL statements at the end of the pre-defined query statements in the web application without the administrator's knowledge. Implement illegal operations in order to deceive the database server into executing unauthorized arbitrary queries, thus further

Jan 28, 2021 pm 06:17 PM

SQL注入

A flip-flop has several steady states

The flip-flop has two stable states, which can represent binary numbers 0 and 1 respectively. It can maintain the stable state without external trigger; under external trigger, the two stable states can be converted into each other, and the converted stable state can be maintained for a long time. This is Enables flip-flops to memorize binary information and is often used as a binary storage unit.

Jan 28, 2021 pm 06:11 PM

触发器

How to set foreign keys in database sql statement

Methods for setting foreign keys in database SQL statements: 1. Add foreign key constraints [alter table add foreign key (foreign key field) references from table main table (primary key field)]; 2. Delete foreign key constraints [alter table table name drop foreig 】.

Jan 26, 2021 pm 03:39 PM

数据库sql外键

What type of database management system is sql?

SQL, the full name of SQL Server, is a relational database management system. The SQL Server database engine provides more secure and reliable storage capabilities for relational and structured data, allowing you to build and manage highly available and high-performance data applications for your business.

Jan 22, 2021 pm 01:45 PM

sqlSQL Server数据库管理系统

Understand inner joins, left outer joins, and right outer joins of sql statements

When you first learn databases, do you have some doubts about the connection query in DQL? Do you know when and what kind of connection query should be used in what scenario? Don't worry, let me introduce to you the understanding of the characteristics and application scenarios of inner joins, left outer joins, and right outer joins in the SQL tutorial column for your reference.

Jan 15, 2021 am 10:20 AM

左连接特点

Troubleshooting SQL injection issues

What is SQL injection? Take a look at the definition of Baidu Encyclopedia. The following SQL tutorial uses an example to explain what SQL injection is: Create a new database, create a table, and add two rows of data: use db1;create table user(id int...

Jan 12, 2021 am 09:22 AM

SQL注入

SQL optimization minimalist rules that you must not know

SQL Tutorial As the standard language of relational database, it is one of the essential skills for IT practitioners. SQL itself is not difficult to learn, and writing query statements is also very easy, but it is difficult to write query statements that can run efficiently.

Jan 02, 2021 am 11:23 AM

sql数据库优化法则

Introducing ten steps to fully understand SQL

Many programmers view SQL as a scourge. SQL is one of the few declarative languages that operates completely differently from the command line languages, object-oriented programming languages, and even functional languages we are familiar with (although some people think that the SQL language is also a functional language ).

Dec 29, 2020 pm 05:57 PM

sql数据库后端运维程序员

Solving SQL problems will definitely take your understanding of MySQL one step further!

The structure of the attribute table (product_props) introduced in the SQL tutorial column is as follows. Data volume is more than 800W. Field name type description id int id pn_id int attribute type pv_id int attribute value product_id int product ID.

Dec 26, 2020 pm 05:42 PM

MySQLSQL

Record slow SQL optimization practice

Introduction to sql tutorial After optimizing sql slow query, we found the following types of problems in our system: 1. No index built: no index built for the entire table; 2. Index miss: there is an index, but the index is under some query conditions Missed; 3. Searched for additional non-essential fields, resulting in table return; 4. Sorting, aggregation...

Dec 25, 2020 pm 05:23 PM

MySQLSQL