[MySQL · water drop plan] the third part - basic concepts of SQL

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Starting today , A column will open , 【MySQL· Water drop plan 】 ,MySQL Series is also a skill that both back-end and front-end need to master . This column will go through a series of detailed explanations MySQL Related to the grammar , And provide some cases to deepen your impression , For everyone to learn MySQL Language builds a certain foundation ！ Welcome to subscribe to this column
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??【MySQL· Water drop plan 】 First words - Basic knowledge of databases ??
??【MySQL· Water drop plan 】 July - Database installation and use ??

?? Third words - SQL Basic concepts of

?? After we installed it yesterday MySQL After environment , Today we officially enter MySQL My teaching , Let's first learn about MySQL Medium SQL What is it? , What's the specific effect ,SQL Classification of grammar , And we write SQL Specification of statement

?? sql What is it?

( S tructured Q uery L anguage) Structured query language , abbreviation SQL. It's a language for communicating with databases .
Then we use Java, Is the most important thing just jdk Environmental Science , No, jdk How can you afford to run Java The procedure , Right . and sql Statement is a language for us to operate the database .

?? sql The role of

• adopt SQL Statement we can operate the database more conveniently 、 surface 、 data .

• SQL It is a standard that database management systems need to follow . Different database manufacturers support SQL sentence , But they all have their own content . We can sql Sentence as our Chinese Mandarin , A language that we can all understand , There are different dialects in different regions , In Guangdong, we can hear Cantonese speaking , And speak Chaoshan dialect and other dialects , That's for databases , In fact, different manufacturers have corresponding dialects , But what? , All support. sql Of the statement , You can understand Mandarin ！

  

?? sql The classification of

sql We can divide into ：

• DDL： Data definition statement , For the creation of libraries and tables 、 modify 、 Delete . keyword ：create,drop,alter etc. ;

• DML： Data manipulation statement , Used to add 、 Delete 、 modify 、 Query database records , And check data integrity . keyword ：insert,delete,update etc. ;

• DQL： Data query language is used to query the database . keyword select;

• DCL： Data control statement , Used to define access rights and security levels for users . And the more important one is ： DML and DQL, Is to add, delete, modify and check ！

?? sql The specification of

• MySQL Database SQL Statement is case insensitive , But the advice Keyword capitalization , Table name 、 Column names in lowercase .

• SQL Statements can be written in one or more lines , It ends with a semicolon , That is, each command should preferably end with a semicolon

• Every command is as needed , You can indent or wrap lines to enhance readability .

• notes ： SQL Unique single line comments ：# Note text single line notes ：-- Annotation text multiline annotation ：/* Note text */

  

?? The end

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