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Mysql database - Advanced SQL statement (2)

2022-07-01 16:58:00 【Seal nine FJ】

MySQL Union set 、 Intersection value 、 No intersection value 、case

1. 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 type

1）UNION

UNION ： There will be no duplicate data values for the generated results , And sort according to the order of the fields 
 grammar ：[SELECT  sentence  1] UNION [SELECT  sentence  2];
 example :
select place_name from destination union select place_name from info;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ character string

2）UNION ALL

UNION ALL ： List the data values of the generated results , With or without repetition 
 grammar ：[SELECT  sentence  1] UNION ALL [SELECT  sentence  2];
 example ：
select place_name from destination union all select place_name from info;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_sql sentence _02

2. Intersection value

  • Take two. SQL The intersection of statement results 
select a.place_name from destination a inner join info b on a.place_name = b.place_name;

select a.place_name from destination a inner join info b using(place_name);

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ stored procedure _03

  • There are no duplicate rows in the two tables , And when there are intersections, use 
select a.place_name from (select place_name from destination union all select place_name from info) a group by a.place_name having count(*) > 1;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ character string _04

  • Take two. SQL The intersection of statement results , And there's no repetition 
select a.place_name from (select b.place_name from destination b inner join info c on b.place_name =c.place_name) a group by a.place_name;   Use group by duplicate removal 

select distinct a.place_name from destination a inner join info b using(place_name);   Inner join intersection ,distinct duplicate removal 

select distinct place_name from destination where (place_name) in (select place_name from info);  Subquery 

select distinct a.place_name from destination a left join info b using(place_name) where b.place_name is not null;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_sql sentence _05

3. No intersection value

  • Show the first SQL Result of statement , And with the second SQL Statement has no result of intersection , And there's no repetition 
select distinct place_name from destination where (place_name) not in (select place_name from info);

select distinct a.place_name from destination a left join info b using(place_name) where b.place_name is null;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ stored procedure _06

4. CASE

  • CASE yes SQL Used for IF-THEN-ELSE And so on 
 grammar ：
SELECT CASE (" Field name ")
  WHEN " Conditions 1" THEN " result 1"
  WHEN " Conditions 2" THEN " result 2"
  ...
  [ELSE " result N"]
  END
FROM " Table name ";

# " Conditions "  It can be a number or a formula . ELSE  Clause is not necessary .

 for example ：
select place_name, case place_name
  when 'beijing' then sales - 200
  when 'tianjin' then sales - 100
  else sales
  end
"new sales",date
from info;
#"New Sales"  Is used for  CASE  The name of that field .

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ stored procedure _07

Null value (NULL) and No value (’’) The difference between

  1. Null value length is 0, Does not occupy a space
  2. NULL The length of the value is null, Occupancy space
  3. is null Cannot determine null value
  4. Null use “=” perhaps “<>” To deal with it
  5. count() When calculating ,NULL Will be ignored , Null values are added to the calculation 
SELECT length(NULL), length(''), length('1');

# Build table 
create table test(test varchar(20));
insert into test values(' ');
insert into test values('123123123');
insert into test values();
insert into test values('11111');
insert into test values('');
select * from test;	

 example ：
select * from test where test is null;
select * from test where test is not null;
select * from test where test = '';
select * from test where test <> '';
select count(test) from test;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ character string _08

MySQL database —— senior SQL sentence ( Two )_sql sentence _09

MySQL Regular expressions of 

 Matching mode 			 describe 									     example 
^ 				 Match the start character of the text  						‘^bd’  Match with  bd  Starting string 
$ 				 Match the end character of the text  						‘qn$’  Match with  qn  a null-terminated string 
. 				 Match any single character 							‘s.t’  Match any  s  and  t  A string with one character between 
* 				 Match zero or more characters before it  				‘fo*t’  matching  t  There is any one in front  o
+ 				 Match preceding characters  1  Times or times 					‘hom+’  Match with  ho  start , At least one back m  String 
 character string  			 Match contains the specified string  						‘clo’  The match contains  clo  String 
p1|p2 			 matching  p1  or  p2 							‘bg|fg’  matching  bg  perhaps  fg
[...] 			 Match any character in the character set  				‘[abc]’  matching  a  perhaps  b  perhaps  c
[^...] 			 Match any characters that are not in brackets  					‘[^ab]’  Match does not contain  a  perhaps  b  String 
{n} 			 Match the previous string  n  Time  					    ‘g{2}’  The match contains  2  individual  g  String 
{n,m}			 Match the previous string at least  n  Time , at most m  Time 		    ‘f{1,3}’  matching  f  least  1  Time , most  3  Time 

     
    
      
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 Grammar format ：

 grammar ：SELECT " Field " FROM " Table name " WHERE " Field " REGEXP { Pattern };
 example ：
use plane
select * from info where place_name regexp '^s';
select * from info where place_name regexp 'an|ing';

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ stored procedure _10

stored procedure

1. brief introduction

  1. MysQL A database stored procedure is a set of procedures designed to perform specific functions SQL Collection of statements
  2. The function of stored procedure is from 5.0 The version just started to support , It can speed up database processing , Enhance the flexibility of database in practical application
  3. 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
  4. The traditional method of operating a database SQL The statement needs to be compiled before execution , Then go ahead and do it , Compare with stored procedures , Obviously, stored procedures are faster to execute , More efficient

2. advantage

  1. After one execution , The generated binary code will reside in the buffer , Improve execution efficiency
  2. SQL Statement plus a collection of control statements , High flexibility
  3. Store on the server side , When called by the client , Reduce network load
  4. Can be called repeatedly , Can be modified at any time , Does not affect client calls
  5. Can complete all database operations , You can also control the information access rights of the database

3. Create stored procedure 

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

 example ：
delimiter $$
create procedure look_info()
  begin
  select * from info;
  end $$
delimiter ;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_sql sentence _11

4. Calling stored procedure 

CALL  The process of ;
 example ：
call look_info;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ stored procedure _12

5. View stored procedures 

SHOW CREATE PROCEDURE [ database .] Stored procedure name ;		# View the specific information of a stored procedure 

 example ：
show create procedure look_info;
show procedure status like '%look_info'\G;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ stored procedure _13

6. Parameters of stored procedure

  1. IN Input parameters ： Indicates that the caller passes a value... To the procedure （ The incoming value can be literal or variable ）
  2. 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 ）
  3. 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 ）
delimiter @@
create procedure test1(in inname char(20))
  begin
  select * from info where place_name = inname;
  end @@
delimiter ;

call test1('shanghai');

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ character string _14

7. 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  The process of ;    # Delete... Only if it exists , If the specified procedure does not exist , There will be a mistake 
DROP PROCEDURE IF EXISTS  The process of ;   # So you can use if exists Delete after confirming the existence , If it does not exist, it will not be deleted .
 example ：
drop procedure if exists test1;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ stored procedure _15

8. Control statement of stored procedure 

create table A (id int);
insert into t values(8);

     
    
      
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MySQL database —— senior SQL sentence ( Two )_sql sentence _16

1） Conditional statements if-then-else-end if

delimiter $$
create procedure test2(in num int)
 begin
 declare var int;
 set var=num*2;
 if var>=10 then
 update t set id=id+1;
 else
 update t set id=id-1;
 end if;
 end $$
 
delimiter ;

call test2(5);

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ character string _17

2） Loop statement while ···· end while

delimiter %%
create procedure test3()
 begin
 declare var int;
 set var=0;
 while var < 5 do
 insert into t values(var);
 set var=var+1;
 end while;
 end %%
 
delimiter ;

call test3;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ stored procedure _18

Sort 

create database exam;
use exam;
create table point(name varchar(20),scores int(5));
insert into point values ('a1',60);
insert into point values ('b2',80);
insert into point values ('c3',68);
insert into point values ('d4',100);
insert into point values ('e5',91);
insert into point values ('f6',55);
insert into point values ('g7',46);
select * from point;

     
    
      
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MySQL database —— senior SQL sentence ( Two )_ character string _19

1. Rank

  • Form self linking (Self Join), Then list the results in order , Before you figure out each line ( Including the line itself ) How many lines are there 
select a1.name, a1.scores,count(a2.scores) rank from point a1,point a2 where a1.scores < a2.scores or (a1.scores = a2.scores and a1.name = a2.name) group by a1.name,a1.scores order by a1.scores desc;
# Statistics scores The value of the field is smaller than its own value scores Fields and name The number of fields is the same , such as ff6 by 6+1=7

     
    
      
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MySQL database —— senior SQL sentence ( Two )_sql sentence _20

MySQL database —— senior SQL sentence ( Two )_ stored procedure _21

  • Add extra ：

2. Count the median 

select scores middle from (select a1.name, a1.scores,count(a2.scores) rank from point a1,class a2 where a1.scores < a2.scores or (a1.scores = a2.scores and a1.name <= a2.name) group by a1.name,a1.scores order by a1.scores desc) a3 where a3.rank = (select (count(*)+1) div 2 from point);

# Each derived table must have its own alias , So alias  A3  There must be 
#DIV  Is in  MySQL  The way to figure out the quotient in the game 

     
    
      
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3. To add up

  • Form self linking (Self Join), Then list the results in order , Before you figure out each line ( Including the line itself ) The sum of 
select A1.*,sum(A2.scores) sum_socores from point A1,point A2 where A1.scores < A2.scores or(A1.scores = A2.scores and A1.name = A2.name) group by A1.name order by A1.scores desc;

     
    
      
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4. Total percentage 

select A1.*,A1.scores/(select sum(scores) from point) per_sum from point A1,point A2 where A1.scores < A2.scores or (A1.scores = A2.scores and A1.name=A2.name) group by A1.name order by A1.scores desc;

#SELECT SUM(Sales) FROM Total_Sales  This query is used to calculate the sum of 
# All in all , We can then divide each row by the sum one by one to find the sum percentage of each row 

     
    
      
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5. Calculate the cumulative total percentage

  • With cumulative total SUM(a2.Sales) Divide by the total to find the cumulative total percentage of each row 
select A1.name,A1.scores,sum(A2.scores),sum(A2.scores)/(select sum(scores) from point) per_sum from point A1,point A2 where A1.scores < A2.scores or (A1.scores = A2.scores and A1.name=A2.name) group by A1.name order by A1.scores desc;

     
    
      
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  • Take a few digits after the decimal point 
select A1.name,A1.scores,sum(A2.scores),truncate(sum(A2.scores)/(select sum(scores) from point),2) ||'%' per_sum from point A1,point A2 where A1.scores < A2.scores or (A1.scores = A2.scores and A1.name=A2.name) group by A1.name order by A1.scores desc;

     
    
      
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