Learn MySQL with teacher Wang: Basic query statement

Learn MySQL with teacher Wang: Basic query statement
Teacher: Wang Shaohua QQ Group No.: 483773664 Learning Content

Basic syntax for query statements

Query data refers to getting the required data from the database. In MySQL, you use the SELECT statement to query the data

The basic grammatical form of a select is as follows

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SELECT属性列表  FROM表名 [ WHERE条件表达式1 ] [ GROUPBY  属性名1  [ HAVING条件表达式2 ] ] [ ORDERBY  属性名2  [ ASC | DESC] ]

Property List: The name of the field to query

Table name: The table you want to query, you can have more than one

Conditional expression 1: Specifying query criteria

Property name 1: Group By this field

Conditional expression 2: data that satisfies the expression can be output

Property Name 2: Sort by the data in this field by hundred rows

ASC: Ascending

DESC: Descending

Two examples
(i) Preparation of data

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createtableemployee(    num intprimary keyauto_increment,    namevarchar(20),    age int,    sex varchar(4),    homeaddr varchar(50) ); insertintoemployee(name,age,sex,homeaddr)values(‘张三‘,26,‘男‘,‘浙江杭州‘); insertintoemployee(name,age,sex,homeaddr)values(‘李四‘,24,‘女‘,‘浙江宁波‘); insertintoemployee(name,age,sex,homeaddr)values(‘王五‘,29,‘男‘,‘浙江台州‘); insertintoemployee(name,age,sex,homeaddr)values(‘赵六‘,21,‘男‘,‘浙江湖州‘); insertintoemployee(name,age,sex,homeaddr)values(‘孙悟空‘,21,‘男‘,‘浙江宁波‘); insertintoemployee(name,age,sex,homeaddr)values(‘猪八戒‘,22,‘男‘,‘浙江宁波‘); insertintoemployee(name,age)values(‘唐僧‘,21);

(b) Simple Enquiry

1	selectnum,name,age,sex,homeaddr fromemployee;

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(iii) contains a WHERE clause and an ORDER BY clause

1	selectnum,name,age,sex,homeaddr from employee where age<26 order bynum DESC;

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Learn MySQL with teacher Wang: Basic query statement