MySQL advanced statement

1、mysql Refine Query

 

1.1、select

select--- Displays all data records for one or more fields in the table 
 grammar ：selcet " Field "  from  " Table name "
​
 give an example ：
------------------------------
select date,store_name,sales from stroe_info  ## Change combination sequence 
select date,store_name from store_info   # Display the specified fields 

 

1.2、distinct

distinct---- Do not display duplicate data records 
 grammar ：select distinct " Field " from " Table name ";
​
 give an example ：
-------------------
select distinct date from store_info;

 

1.3、where

where---- Conditional query 
 grammar ：select " Field " from " Table name " where " Conditions ";
​
 give an example ：
-------------------
select store_name from store_info where sales>1000;
select * from store_info where sales>1000;

 

1.4、and or

and or---- And   or 
 grammar ：select  " Field "  from " Table name " where " Conditions 1"  and or " Conditions 2";
​
 give an example ：
-------------------
select * from store_info where sales>500 and sales<1000;
select * from store_info where (sales>200 and sales<500) or sales>1000;

 

1.5、in

in---- Data records showing known values 
 grammar ：select  " Field " from " Table name " where " Field " in (' value 1',' value 2'....);
​
 give an example ：
-------------------
 select * from store_info where store_name in ('Boston','Houston');
 select * from store_info where store_name not in ('Boston','Houston');

 

1.6、between

between---- Display data records in the range of two values 
 grammar ：select  " Field " from " Table name " where " Field " between ' value 1' and ' value 2';
​
 give an example ：
-------------------
select * from store_info where sales between 500 and 1500;
select * from store_info where date  between '2020-12-06' and '2020-12-10';

 

1.7、 wildcard

 Wildcards are both and like Used together 
%: Percentage sign 0 individual , One or more characters 
——： The underline represents a single character 
​
​
'A_Z':  With 'A' At first , With 'z' Is another string with one at the end .
----------- give an example ：'ABZ'  and 'A2z'  In line with this , and 'AKKZ'  It does not accord with 
​
'ABC%':'ABC'  Starting string .
------------ give an example ：'ABCD'  and 'ABCABC'.  All fit the pattern 
​
'%XYZ':  With 'XYZ' a null-terminated string .
------------ give an example ：'wXYZ' and 'ZZXYZ'  All fit the pattern 
​
'%AN%':  contain 'AN' The string of this pattern 
------------ give an example ：'LOS ANGELES'  and ' SAN FRANCISCO'  accord with 
​
'_AN%': All the second letters are 'A' And the third letter is 'N'  String .
------------ give an example ：'SAN FRANCISCO'  accord with ,'los ANGELES' Do not conform to the 

 

1.8、order by

order by---- Sort by keyword 
 grammar ：select  " Field " from " Table name " where " Field " order by " Field " [ASC DESC]
##ASC  Is sorted in ascending order , Is the default sort method 
##DESC  It's sorted in descending order 
​
 give an example ：
-------------------
mysql> select * from store_info order by sales;   ## Ascending 
mysql> select * from store_info order by sales asc; # Ascending 
mysql> select * from store_info order by sales desc; ## In reverse order 

 

2、mysql Database functions

2.1、 Mathematical functions

 Mathematical functions 
abs(x)           return x The absolute value of 
rand()           return 0 To 1 The random number 
mod(x,y)         return x Divide y The remainder after 
power(x,y)       return x Of y Power 
round(x)         Return from x The nearest integer 
round(x,y)       Retain x Of y The rounded value of a decimal place 
sqrt(x)          return x The square root of 
truncate(x,y)       Return to digital x Truncated to y A decimal value 
ceil(x)             Returns greater than or equal to x Minimum integer of 
floor(x)            Returns less than or equal to x Maximum integer for 
greatest(x1,x2...)  Returns the maximum value in the collection 
least(x1,x2....)    Returns the smallest value in the set 

 

2.2、 Aggregate functions

 Aggregate functions 
avg()            Returns the average value of the specified column 
count()          Returns the value of the specified column NULL  The number of values 
min()            Returns the minimum value of the specified column 
max()            Returns the maximum value of the specified column 
sum(x)           Returns the sum of all values in the specified column 

 

2.3、 String function

 String function :
trim()            Returns a value with the specified format removed 
concat (X, y)     The parameters that will be provided x and y Concatenate into a string 
substr (x,y)      Get from string x No y A string starting at a position , Follow substring()  Functions work the same 
substr (X,Y,z)    Get from string x No y The starting length of a position is z String 
length(x)         Return string x The length of 
replace (x,Y1Z)   The string z Alternative string x String in y
upper (x)         The string x All of the letters of the alphabet become capital letters 
lower (x)         The string x All of the letters of the are changed into lower case letters 
left (x,y)        Return string x Before y Characters 
right (x,y)       Return string x After y Characters 
repeat (x,y)      The string x repeat γ Time 
space (x)         return x A space 
strcmp (x,y)      Compare x and y, The value returned can be -1,0,1
reverse (x)       The string x reverse 
​
--------------------------------------------------
 If sql_mode Open the PIPES_AS_CONCAT,"||" Treat as a continuous operator of a string, not an or operator , And string splicing function concat Similar , This is the sum of Oracle The database is used in the same way 

 

3、mysql Refine Query 2

3.1、group by

group by------ Yes group by The query results of the following fields are summarized and grouped , Usually used in combination with aggregate functions 
group by There is a principle , Where there are group by The fields that appear later , Must be in select Behind the 
 Where there are select Later on , Fields that do not appear in the aggregate function , Must appear in group by Back 
​
--------------
 grammar ：select " Field 1",SUM(" Field 2") from " Table name " group by " Field 1";
​
 give an example ：
select store_name from store_info group by store_name;

 

3.2、having

having The existence of sentences makes up for where Keywords cannot be combined with aggregate functions 
​
----------------
 grammar ：select " Field 1",SUM(" Field 2") from " Table name " group by " Subsegment 1" having ( Function conditions );
​
 give an example ：
mysql> select store_name,sum(sales) from store_info group by store_name having sum(sales) > 1000;

 

3.3、 Alias

 Alias ---- Field alias   Table alias 
 grammar : SELECT " Form alias ". " Field 1” [AS] " Field alias " FROM " Table name ” [AS] " Form alias ”;
​
 give an example ：
mysql> select store_name,sum(sales) as total_sales from store_info group by store_name having sum(sales) > 1000;

 

3.4、 Subquery

-----  Subquery ---- Connect tables , stay WHERE  Clause or HAVING  Clause to insert another sQL sentence 
 grammar : SELECT " Field 1" FROM " form 1" WHERE " Field 2”[ Comparison operator ] 
# External query 
(SELECT " Field 1" FROM " form 2" WHERE " Conditions ") ;
# Internal query 
​
#### Can be symbolic operators , for example =、>、<、>=、<=、 It can also be a literal operator , for example like、IN、between

3.5、exists

exists--- It is used to test whether the inner query produces any results , Whether Boolean value is true or not 
 grammar ：select " Field 1" from " form 1" where exists (select * from " form 2" where " Conditions ")

4、mysql Three connections

4.1、 Internal connection

inner join: Only rows with equal join fields in two tables are returned 
​
 give an example :
select * from location A INNER JOIN store_info B ON A.store_name = B.store

 

4.2、 Left connection

left join: Returns records that include all records in the left table and the same join field in the right table 
​
 give an example :
select * from location A left join store_info B ON A.store_name = B.store_name;

 

4.3、 The right connection

right join: Returns records that include all records in the right table and join fields in the left table 
​
 give an example ：
select * from scores A right join students B on A.stuid = B.stuid;

5、 View

It can be thought of as a virtual table or a storage query

（1） The difference between a view and a table is , There is the actual stored information in the form , And a view is a structure built on a table , It doesn't actually store data itself .

（2） The temporary table disappears automatically when the user exits or loses the connection to the database , And the view doesn't disappear .

（3） Views don't contain data , Just store its definition , Its purpose is to simplify complex queries . For example, you need to query several tables , But also to carry out statistical sorting and other operations , Write SQL Sentences can be cumbersome , Join several tables with views , Then query the view , Just like querying a table , Very convenient .

# grammar ：
CREATE VIEW " View table name " AS "SELECT  sentence ";
​
----------
 give an example ：
create view V_REGION_SALES as select A.Region REGION,SUM(B.Sales) SALES from location A,
store_info B where A.store_name =B.store_name group by REGION;
​
SELECT * FROM V_REGION_SALES;
​
DROP VIEW V_REGION_SALES;

 

6、UNION combine

Put two sql The results of the statement are combined , Two sql The fields generated by the statement need to be of the same data record type

UNION: The data record value of the generated result will not be repeated , And sort according to the order of the fields 
 grammar : [SELECT  sentence 1] UNION [SELECT  sentence 2];
​
UNIONALL: List the data record values of the generated results , With or without repetition 
 grammar : [SELECT  sentence 1] UNION ALL [SELECT  sentence 2] ;
​
 give an example ：
------------------
select store_name from location union select store_name from store_info;
select store_name from location union all select store_name from store_info;

 

7、 Intersection value

Take two. SQL The intersection of statement results

----  Intersection value ---- Take two. sQL The intersection of statement results 
SELECT A.Store_ Name FROM location A INNER JOIN Store_ Info B ON A.Store_ Name = B.Store_ Name ; 
SELECT A.Store_ Name FROM location A INNER JOIN Store_ Info B USING(Store_ Name) ;
​
# Take two. sQL The intersection of statement results , And there's no repetition 
SELECT DISTINCT A.Store_ Name FROM location A INNER JOIN Store_ Info B USING (Store_ Name) ;
SELECT DISTINCT Store_ Name FROM location WHERE (Store_ Name) IN (SELECT Store_ Name FROM Store_ Info);
SELECT DISTINCT A.Store_ Name FROM location A LEFT JOIN Store_ Info B USING(Store_ Name) WHERE B.Store_ Name IS NOT NULL;
SELECT A.Store_ Name FROM (SELECT B.Store_ Name FROM location B INNER JOIN Store_ Info C ON B.Store_ Name = C.Store_ Name) A
GROUP BY A. Store_ Name;

​

7、 Null value (NULL) and No value (’ ') The difference between

1. The length of no value is 0, Not taking up space ; and NULL The length of the value is NULL, It takes up space .
2. Is NULL perhaps Is NOT NULL,  It is used to judge whether the field is NULL  Or not NULL, It is impossible to find out whether there is nothing .
 The judgment without value uses =' perhaps <>" To deal with it .<> The representative is not equal to .
4. Through count () When specifying the number of rows in the field statistics , If you encounter NULL  The value is automatically ignored , If there is no value, it will be added to the record for calculation .

8、 Regular expressions

----  Regular expressions ----
 Matching mode                    describe 
^                    Match the start character of the text 
$                    Match the end character of the text 
.                    Match any single character 
*                    Match zero or more characters before it 
+                    Match preceding characters 1 Times or times 
 character string                 Match contains the specified string 
p1|p2                matching p1 or p2
[...]                Match any character in the character set 
[^...]               Match any characters that are not in brackets 
{n}                  Match the previous string n Time 
{n,m}                Match the previous string at least n Time , at most m Time 


 grammar ：SELECT  " Field " FROM " Table name ”WHERE " Field " REGEXP { Pattern };
SELECT * FROM Store_ Info WHERE Store_ Name REGEXP 'os' ;
SELECT * FROM Store_ Info WHERE Store_ Name REGEXP I^[A-G] ' ;
SELECT * FROM Store_ Info WHERE Store_ Name REGEXP 'Ho | Bo' ;

9、 stored procedure

 A stored procedure is a set of functions to accomplish sQL Statement set .
 In the process of using stored procedures, common or complex work is used in advance sQL The statement is written and stored with a specified name , This process is compiled and optimized and stored in the database server .
 When you need to use this stored procedure , Just call it . Stored procedures perform better than traditional SQL Faster 、 More efficient execution .

Advantages of stored procedures

• After one execution , The generated binary code will reside in the buffer , Improve execution efficiency

• SQL Statement plus a collection of control statements , High flexibility

• Store on the server side , When called by the client , Reducing network load can be called repeatedly , Can be modified at any time , Does not affect client calls

• Can complete all database operations , You can also control the information access rights of the database

9.1、 Create stored procedure

DELIMITER $$                      # Change the closing sign of the statement from a semicolon ; Temporarily changed to two $$( It can be custom )
CREATE PROCEDURE Proc()           # Create stored procedure , The process name is Proc, With no arguments 
> BEGIN                           # The process body takes the keyword BEGIN Start 
-> select * from Store_ Info;     # Process style sentences 
-> END $$                         # The process body takes the keyword END end 
DELIMITER ;                       # Returns the ending symbol of the statement to a semicolon ;

9.2、 Calling stored procedure

call proc;

9.3、 View stored procedures

SHOW CREATE PROCEDURE [  database . ] Stored procedure name ;
# View the specific information of a stored procedure 
​
SHOW CREATE PROCEDURE Proc;
SHOW PROCEDURE STATUS [LIKE ' 8Proc8' ] \G

9.4、 Parameters of stored procedure

IN Input parameters : Indicates that the caller passes a value... To the procedure ( The incoming value can be literal or variable )
OUT Output parameters : Indicates that the procedure passes out a value to the caller ( Multiple values can be returned ) ( Outgoing values can only be variables )
INOUT Input/output parameter : It means that the caller passes in a value to the procedure , It also indicates that the procedure passes out a value to the caller ( Values can only be variables )

9.5、 Delete stored procedure

 The method to modify the contents of stored procedures is to delete the original stored procedures , Then create a new stored procedure with the same name .
DROP PROCEDURE IF EXISTS Proc;
# Delete... Only if it exists , Don't add IF EXISTS  when , If the specified procedure does not exist , Then there is an error 

9.6、 Control statement of stored procedure

9.6.1、 Conditional statements ：if-then-else .... end if

DELIMITER $$
CREATE PROCEDURE proc2 (IN pro int)
-> begin
-> declare var int ;
-> set var=pro*2;
if var>=10 then
-> update t set id=id+1;
-> else
-> update t set id=id-1;
-> end if;
-> end $$;
​
DELIMITER ;
​
CALL Proc2 (6) ;

9.6.2、while......end while

DELIMITER $$                                            # Modify the default terminator to $$
-> create procedure yxp()                           # Create stored procedure yxp
-> begin                                                # The process body takes the keyword begin Start 
-> declare i int;                               # Defining variables i by int type （ Maximum length 10）
-> set i = 1;                                           # Set up i = 1;
->  while i <= 100                                  # Use while loop ,i To be less than 100
-> do insert into nametest(name,age) values
            # If the conditions are met, add data , The content is variable i
-> set i=i+1;                                       # Variable i Add... After each cycle 1                             
-> end while;                                           # end while loop 
-> end $$                                               # End of creating stored procedure 
delimiter ;                                             # Modify the default terminator to the original ;
CALL proc6;                                             # call yxp stored procedure