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- What are the transaction isolation levels of the database?
- In database operations, in order to effectively ensure the correctness of concurrently read data, the transaction isolation level is proposed. A general database includes four isolation levels: read uncommitted, read committed, repeatable read, and serialized; different isolation levels handle transactions differently.
- SQL 25239 2019-06-12 17:08:33
- What are the commonly used SQL statements?
- Commonly used SQL statements include show databases; create database db1; show create; show tables; database db1; create database db1, etc.
- SQL 5339 2019-06-10 16:38:32
- what is json
- JSON (JavaScript Object Notation) is a lightweight data exchange format that is easy to read and write, as well as easy to be parsed and generated by machines. .
- SQL 12693 2019-06-17 15:20:37
- What is the order of sql execution?
- The SQL statement is divided into 11 steps. The FROM operation is always executed first, and the LIMIT operation is executed last. Each operation will generate a virtual table, which is used as an input for processing. However, these virtual tables are transparent to the user, and the last virtual table will be returned as a result.
- SQL 29259 2019-06-17 15:20:50
- What are the commonly used relational databases?
- Simply put, a relational database is a database composed of multiple two-dimensional row and column tables that can be connected to each other. The current mainstream relational databases include Oracle, DB2, Microsoft SQL Server, Microsoft Access, MySQL, etc.
- SQL 98666 2019-06-06 13:11:10
- Several methods of sql optimization
- To optimize queries, you should try to avoid full table scans. You should first consider building indexes on the columns involved in where and order by. You should try to avoid using or in the where clause to connect conditions, otherwise the search engine will give up using the index and Perform a full table scan.
- SQL 27106 2019-06-05 16:04:19
- Database type
- Databases are divided into relational databases and non-relational databases. Commonly used relational databases include MySQL, MariaDB database, SQL Server database, and Access database; commonly used non-relational databases include memcached, Redis, MongoDB, Cassandra, etc.
- SQL 4786 2019-06-05 10:41:49
- What are the differences between delete and truncate
- The difference between delete and truncate commands: delete is a data manipulation language (DML) command, which uses row-level locking, and can delete single, multiple or all records from the table; while truncate is a data definition language (DDL) command, which uses table-level locking. , delete all records and table structures from the database. etc.
- SQL 42546 2019-06-17 15:31:04
- Why use redis?
- Redis is an open source log-type, [Key-Value] database written in ANSI C language, supports network, can be memory-based and persistent, and provides APIs in multiple languages; using redis can greatly improve system access efficiency.
- SQL 18504 2020-09-18 10:11:00
- When do you need to use redis?
- When you need to use redis: 1. Data that does not need to be updated in real time but consumes a lot of database data; 2. Data that needs to be updated in real time, but the update frequency is not high; 3. The number of visits at a certain moment is very high and the updates are also very frequent. data.
- SQL 14294 2020-09-18 10:18:10
- Is the redis database free?
- Redis is completely open source and free. It is an open source log-type Key-Value database written in ANSIC language, abiding by the BSD protocol, supporting the network, memory-based and persistent, and providing APIs in multiple languages.
- SQL 5624 2019-05-21 10:44:20
- How to perform sql injection
- Methods for SQL injection: 1. Force an error; 2. Use non-mainstream channel technology; 3. Use special characters; 4. Use conditional statements; 5. Use stored procedures; 6. Avoid input filtering technology, etc.
- SQL 26389 2020-09-15 10:50:23
- How to recover deleted data from sql database
- SQL database data recovery method: 1. Back up the transaction log of the current database [BACKUP LOG [database name] TO disk= N'backup file name' WITH NORECOVERY]; 2. Restore a full backup before accidental deletion; 3. Restore the database Restore to a point in time before accidental deletion.
- SQL 36341 2020-09-15 17:53:34
- Is SQL easy to learn?
- In fact, everything has two sides. It will become easier as long as you work hard, believe in yourself. There are no shortcuts to learning, you can only rely on hard work, and if you are a programmer learning databases, you don’t need to know much, just know the basic operations. If you specialize in databases, you will need a lot more.
- SQL 10754 2019-05-17 16:56:35
- how to learn sql
- How to learn sql: first you need to master certain basic knowledge of database; then you need to find some sql exercises to do; finally you need to learn advanced sql usage and techniques. sql is a database query and programming language used to access data and query, update and manage relational database systems.
- SQL 18528 2020-09-16 10:00:14
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