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MySQL advanced (Advanced) SQL statement (II)

2022-07-02 03:15:00 【Richard_ Chiang】

MySQL senior ( Advanced )SQL sentence （ Two ）

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

MySQL senior ( Advanced )SQL sentence （ Two ）_bash

1、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 type 
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 senior ( Advanced )SQL sentence （ Two ）_mysql_02

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 senior ( Advanced )SQL sentence （ Two ）_mysql_03

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 senior ( Advanced )SQL sentence （ Two ）_bash_04

  • There are no duplicate rows in the two tables , The row of the other table is repeated and does not apply , Use when two tables do have intersecting rows 
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 senior ( Advanced )SQL sentence （ Two ）_sql sentence _05

  • 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;

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

select distinct place_name from destination where (place_name) 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 not null;

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_mysql_06

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 senior ( Advanced )SQL sentence （ Two ）_bash_07

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 - 50
  when 'kunming' then sales - 20
  else sales
  end
"new sales",date
from info;
#"New Sales"  Is used for  CASE  The name of that field .

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_sql sentence _08

5、 ... and 、 Sort

Case study ：

create database school;
use school;
create table class(name varchar(20),scores int(5));
insert into class values ('aa1',80);
insert into class values ('bb2',100);
insert into class values ('cc3',78);
insert into class values ('dd4',94);
insert into class values ('ee5',66);
insert into class values ('ff6',53);
insert into class values ('gg7',77);
select * from class;

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_mysql_09

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 class 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;
# 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 senior ( Advanced )SQL sentence （ Two ）_bash_10

2、 Count the median 

select scores middle from (select a1.name, a1.scores,count(a2.scores) rank from class 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 class);
# 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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MySQL senior ( Advanced )SQL sentence （ Two ）_mysql_11

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 class A1,class 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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MySQL senior ( Advanced )SQL sentence （ Two ）_bash_12

4、 Total percentage 

select A1.*,A1.scores/(select sum(scores) from class) per_sum from class A1,class 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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MySQL senior ( Advanced )SQL sentence （ Two ）_sql sentence _13

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 class) per_sum from class A1,class 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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MySQL senior ( Advanced )SQL sentence （ Two ）_sql sentence _14

  • Take a few digits after the decimal point 
select A1.name,A1.scores,sum(A2.scores),truncate(sum(A2.scores)/(select sum(scores) from class),2) ||'%' per_sum from class A1,class 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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MySQL senior ( Advanced )SQL sentence （ Two ）_bash_15

6、 ... and 、 Null value (NULL) and No value (‘’) The difference between

  • The length of no value is 0, Not taking up space ; and NULL The length of the value is NULL, It takes up space .
  • IS NULL perhaps IS NOT NULL, It is used to judge whether the field is NULL Or not NULL, Can't find out if it's worthless .
  • The judgment without value uses =’‘ perhaps <>’' To deal with it .<> The representative is not equal to .
  • 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 .
SELECT length(NULL), length(''), length('1');

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_sql sentence _16

  • test 
# Build table 
create table test(test varchar(20));
insert into test values(' ');
insert into test values('123123');
insert into test values();
insert into test values('1111');
insert into test values('');
select * from test;	

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_mysql_17

 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 senior ( Advanced )SQL sentence （ Two ）_bash_18

MySQL senior ( Advanced )SQL sentence （ Two ）_mysql_19

7、 ... and 、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

Grammar format ：

 grammar ：SELECT " Field " FROM " Table name " WHERE " Field " REGEXP { Pattern };
 example ： I use the library of the above experiment here 
use plane
select * from info where place_name regexp '^b';
select * from info where place_name regexp 'ei|un';

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_bash_20

8、 ... and 、 stored procedure

1、 The concept of 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 .

2、 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 , Reduce 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

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 $$
create procedure cha_info()
  begin
  select * from info;
  end $$
delimiter ;

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_mysql_21

4、 Calling stored procedure 

CALL  The process of ;
 example ：
call cha_info;

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_bash_22

5、 View stored procedures 

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

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

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_sql sentence _23

6、 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 ）

for example ：

delimiter !!
create procedure test1(in inname char(20))
  begin
  select * from info where place_name = inname;
  end !!
delimiter ;

call test1('chengdu');

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_bash_24

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 senior ( Advanced )SQL sentence （ Two ）_mysql_25

8、 Control statement of stored procedure 

create table t (id int);
insert into t values(10);

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_sql sentence _26

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

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

call test2(6);

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_mysql_27

MySQL senior ( Advanced )SQL sentence （ Two ）_sql sentence _28

（2） Loop statement while/end while

delimiter $$
create procedure test3()
 begin
 declare var int;
 set var=0;
 while var<6 do
 insert into t values(var);
 set var=var+1;
 end while;
 end $$
 
delimiter ;

call test3;

     
    
      
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MySQL senior ( Advanced )SQL sentence （ Two ）_sql sentence _29

MySQL senior ( Advanced )SQL sentence （ Two ）_sql sentence _30

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本文为[Richard_ Chiang]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/02/202202152003548375.html

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