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What are the nine commonly used statements in SQL

The nine commonly used statements in SQL include create database, drop database, sql server, backup database, drop table tabname, drop index idxname, drop view view

Jun 15, 2019 am 11:16 AM

sql

What is the command to modify the table structure in sql statement?

The command in the SQL statement to modify the table structure is ALTER TABLE. The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.

Jun 14, 2019 pm 04:28 PM

sql修改表结构

What is the sql modification statement?

The sql modification statement is an UPDATE statement. The UPDATE statement is used to update existing records in the table. Please pay attention to the WHERE clause in the SQL UPDATE statement! The WHERE clause specifies which record or records need to be updated. If you omit the WHERE clause, all records will be updated!

Jun 14, 2019 pm 03:40 PM

sql修改

What is the database add statement?

The database add statement is the INSERT INTO statement. The INSERT INTO statement is used to insert new records into the table. The INSERT INTO statement can be written in two forms: the first form does not need to specify the column name of the data to be inserted, and only needs to provide the inserted value; the second form requires Specify the column name and the value to be inserted.

Jun 14, 2019 am 11:51 AM

数据库添加

A brief discussion of database stored procedures

Database stored procedures: Stored procedures are methods, with similar method names, variables to be passed by the method, and return results, so stored procedures have stored procedure names, stored procedure parameters, and return values.

Jun 14, 2019 am 11:25 AM

数据库存储过程

Detailed explanation of database stored procedures

Stored procedures can be viewed as stored t-sql scripts in the database. Why use stored procedures? 1. Increase performance; 2. Enhance security; 3. Use non-database technology in transact-sql; 4. Programming mode - use external programming language calls.

Jun 14, 2019 am 11:12 AM

数据库存储过程

What are the two methods of database backup?

The two methods for database backup are: 1. Use mysqldump combined with the exec function for database backup; 2. Use the [php+mysql+header] function for database backup.

Jun 14, 2019 am 11:02 AM

数据库备份

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.

Jun 12, 2019 pm 05:08 PM

数据库事务隔离级别事务

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.

Jun 10, 2019 pm 04:38 PM

常用sql语句

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. .

Jun 10, 2019 pm 01:16 PM

json

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.

Jun 10, 2019 am 10:36 AM

sql执行顺序

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.

Jun 06, 2019 pm 01:11 PM

关系型数据库数据库

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.

Jun 05, 2019 pm 04:04 PM

sql优化

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.

Jun 05, 2019 am 10:41 AM

数据库