MySQL advanced (Advanced) SQL statement (I)

Catalog

• Environmental Science ： Create table
• One 、order by sentence
• Two 、 Ascending and descending （ASC and DESC）
• 3、 ... and 、select Inquire about
• Four 、and/or- And / or
• 5、 ... and 、where
• 6、 ... and 、distinct（ Query does not duplicate records ）
• 7、 ... and 、group by（ Group results ）
• 8、 ... and 、limit
• Nine 、alias（ Set alias ）

Environmental Science ： Create table

mysql> show databases;

mysql> use kgc

mysql> show tables;

mysql> create table ky19;

mysql> create table ky19 (id int,name varchar(10)primary key not null,score decimal(5,2),address varchar(20),hobbid int(5));

mysql> insert into ky19 values(1,'zhusang',100,'riben',2);

mysql> insert into ky19 values(2,'liangsang',59.89,'taiguo',2);

mysql> insert into ky19 values(3,'wusang',80,'miandian',3);

mysql> insert into ky19 values(4,'chenbao',99,'ouzhou',4);

mysql> insert into ky19 values(5,'gangzi',88,'hanguo',5);

mysql> insert into ky19 values(6,'xiangxi',66,'shanghai',3);

mysql> insert into ky19 values(7,'jianjian',87,'cv',6);

mysql> select * from ky19;

One 、order by sentence

( increase 、 Delete 、 Change 、 check )
Yes MysQL Database query , In addition to basic queries , Sometimes you need to process the result set of the query . For example, take only 10 Data 、 Sort or group the query results, etc .

Sort by keyword
PS: Analogy to windows Task manager , Use SELECT Statement can transfer the required data from MySQL From the database , If you sort the results of the query , have access to ORDER BY Statement to sort statements , And finally return the sorted results to the user . The sorting of this statement can not only be for a certain field , You can also target multiple fields

grammar

SELECT column1,column2,... FROM table_name ORDER BY column1,column2,...


---- ORDER BY ---- Sort by keyword 
 grammar ：SELECT " Field " FROM " Table name " [WHERE " Conditions "] ORDER BY " Field " [ASC, DESC];
#ASC  It's sorted in ascending order , Is the default sort method .
#DESC  It's sorted in descending order .

Two 、 Ascending and descending （ASC and DESC）

ASC：
It's sorted in ascending order , Is the default sort method , namely ASC It can be omitted .SELECT If no specific sorting method is specified in the statement , By default ASC Sort by .

DESC：
Is arranged in descending order . Of course ORDER BY You can also use WHERE Clause to further filter the query results .

3、 ... and 、select Inquire about

---- SELECT ---- Display all data of one or more fields in the table 
 grammar ：SELECT " Field " FROM " Table name ";
SELECT Store_Name FROM Store_Info;

Four 、and/or- And / or

---- AND OR ---- And   or 
 grammar ：SELECT " Field " FROM " Table name " WHERE " Conditions 1" {[AND|OR] " Conditions 2"}+ ;
SELECT Store_Name FROM Store_Info WHERE Sales > 1000 OR (Sales < 500 AND Sales > 200);

5、 ... and 、where

--- WHERE ---- Conditional query 
 grammar ：SELECT " Field " FROM " Table name " WHERE " Conditions ";

6、 ... and 、distinct（ Query does not duplicate records ）

---- DISTINCT ---- Don't show duplicate data 
 grammar ：SELECT DISTINCT " Field " FROM " Table name ";
SELECT DISTINCT Store_Name FROM Store_Info;

Define two fields name,hobbid With name As counting statistics , In the query table score Greater than or equal to 80 In the process of hobbid grouping

7、 ... and 、group by（ Group results ）

adopt SQL The result of the search , You can also group the total , Use GROUP BY Statement to implement ,GROUP BY Usually used in conjunction with aggregate functions , Common aggregation functions include : Count （ COUNT) 、 Sum up （SUM）、 Average （AVG）、 Maximum （MAX)、 minimum value （MIN),GROUP BY When grouping, the results can be grouped according to one or more fields .
grammar

SELECT column_name,aggregate_function (column_name)FROM table_name WHERE column_nameoperator valueGROUP BY column name;


---- GROUP BY ---- Yes GROUP BY Summarize and group the query results in the following fields , Usually used in combination with aggregate functions 
GROUP BY  There is a principle , Namely  SELECT  In all the following columns , Columns that do not use aggregate functions , Must appear in GROUP BY Back .

 grammar ：SELECT " Field 1", SUM(" Field 2") FROM " Table name " GROUP BY " Field 1";

8、 ... and 、limit

Limit result entries ( limit )
limit Limit the result record of output
In the use of MySQL SELECT Statement to query , The result set returns all matching records （ That's ok ）. Sometimes you just need to return the first line or the first few lines , And that's where it comes in LIMIT Clause .

grammar

SELECT column1,column2,... FROM table_name LIMIT [offset, ] number

LIMIT The first parameter is the position offset （ Optional parameters ), It's settings MysQL Which line to start with . If the first parameter is not set , It will start from the first record in the table . It should be noted that , The position offset of the first record is 0, The second is 1, And so on . second : The first parameter is to set the maximum number of returned record rows .

Nine 、alias（ Set alias ）

Set alias ( alias ——》as )
stay MysQL When inquiring , When the name of the table is long or some fields in the table are long , For the convenience of writing or
Use the same table multiple times ," You can set aliases for fields, columns, or tables . Use aliases directly when using , Simple and clear , enhance readability
grammar

 For column aliases :SELECT column_name AS alias_name FROM table_name;
 For table aliases :SELECT column_name (s)FROM table_name As alias_name;

In the use of AS after , It can be used alias_name Instead of table_name, among As i The statement is optional .AS Later alias , It is mainly used to provide temporary names for columns or tables in the table , Use in the process of checking , The actual table name or field name in the library will not be changed