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High level application of SQL statements in MySQL database (II)

2022-07-02 09:45:00 【Guyu Taoist priest】

1、CREATE VIEW View
2.UNION combine
3. Intersection value
4. No intersection value
5.CASE
3、 ... and 、 Regular expressions
Four 、 stored procedure

1. summary
2. Advantages of stored procedures
3. Create stored procedure
4. Calling stored procedure
5. View stored procedures

6. Parameters of stored procedure
7. Delete stored procedure

8. Control statement of stored procedure
8.1 Conditional statements （if）
8.2 Loop statement （while）

1、CREATE VIEW View

View ： Can be treated as a virtual table or stored query .
The difference between a view and a table is , There are actually stored data in the table , And a view is a structure built on a table , It doesn't actually store data itself .

The temporary table disappears automatically after the user exits or disconnects from the database , The view does not .

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

grammar ：CREATE VIEW View table name AS SELECT sentence ;
example :

select A.region,SUM(B.money) from REGION AS A inner join FARE AS B on A.site = B.site GROUP BY region;
create view ST AS select A.region,SUM(B.money) from REGION AS A inner join FARE AS B on A.site = B.site GROUP BY region;

show tables;
select * from ST;

drop view ST;
# Delete view table 

     
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MySQL database SQL High level use of statements （ Two ）_ character string

2.UNION combine

Put two SQL The results of the statement are combined , Two SQL The fields generated by the statement need to be 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

SELECT sentence 1 UNION SELECT sentence 2;
 or 
SELECT sentence 1 UNION ALL SELECT sentence 2;
#UNION ALL： List the data values of the generated results , With or without repetition 

 example ：
select region from REGION union select money from FARE;
select site from REGION union select site from FARE;
select site from REGION union all select site from FARE;

     
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MySQL database SQL High level use of statements （ Two ）_ character string _03

MySQL database SQL High level use of statements （ Two ）_ stored procedure _04

3. Intersection value

Take two. SQL The intersection of statement results
example ：

select * from FARE;
select * from REGION;

select site from (select A.site from FARE A inner join REGION B on A.site = B.site) C group by C.site;

select site from FARE where site in (select site from REGION);

     
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MySQL database SQL High level use of statements （ Two ）_ stored procedure _05

4. No intersection value

Show the first SQL Result of statement , And with the second SQL Statement has no result of intersection , It can't be repeated
example ：

select distinct site from FARE where (site) not in (select site from REGION);

select A.*,B.* from FARE A left join REGION B using(site);
select distinct site from FARE A left join REGION B using(site) where B.site is null;

     
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MySQL database SQL High level use of statements （ Two ）_mysql_07

5.CASE

yes SQL Used as a IF-THEN-ELSE And so on
usage ：

SELECT CASE （ Field name ）
    WHEN  Conditions 1 THEN   result 1
	WHEN  Conditions 2 THEN  result 2
	……
	ELSE  result N
	END
FROM  Table name 

# The condition can be a numerical value or a formula , And  ELSE  Clause is not required 

 example ：
select * from FARE;

mysql> select case site
    -> when 'najing' then money + 500
    -> when 'tianjin' then money - 500
    -> else money * 2
    -> end
    -> A,site
    -> from FARE;

     
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MySQL database SQL High level use of statements （ Two ）_ stored procedure _08

3、 ... and 、 Regular expressions

The specific application is shown in the following table ：

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
[…]	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
p1	p2	matching p1 or p2

usage ：

SELECT  Field  FROM  Table name  WHERE  Field  REGEXP  Matching mode 

 example ：
select * from FARE where site regexp '^[n]';
select * from FARE where site regexp '[n]';
select * from FARE where site regexp 'jin|jing';

     
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MySQL database SQL High level use of statements （ Two ）_ stored procedure _09

Four 、 stored procedure

1. summary

A stored procedure is a set of functions to accomplish SQL Statement set
And I learned before Shell The function is almost , In essence, it is the reuse of code
Further details ：
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

DELIMITER $$                # Change the closing sign of the statement from a semicolon ; Temporary modification , In case something goes wrong , You can customize 
CREATE PROCEDURE XXX()  	# Create stored procedure , Custom procedure name ,（） With parameters 
 	BEGIN   		    	# The process body takes the keyword BEGIN Start 
 	select * from xxx;  	# Process style sentences 
 	END$$    				# The process body takes the keyword END ending 
DELIMITER ; 			    # Returns the ending symbol of the statement to a semicolon 

 example ：
mysql> delimiter $$
mysql> create procedure XCF()
    -> begin
    -> select * from FARE;
    -> end $$
Query OK, 0 rows affected (0.00 sec)

mysql> delimiter ;

     
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MySQL database SQL High level use of statements （ Two ）_ character string _10

4. Calling stored procedure

MySQL database SQL High level use of statements （ Two ）_ stored procedure _11

5. View stored procedures

usage ：

show create procedure [ database .] Stored procedure name ; 	  # View the specific information of a stored process 
show create procedure XXX;
show procedure status [like '%XXX%'] \G

 example ：
show create procedure train_ticket.XCF\G
show procedure status like '%XCF%'\G

     
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MySQL database SQL High level use of statements （ Two ）_ stored procedure _12

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 ）
example ：

mysql> delimiter $$
mysql> create procedure XCF0(IN place char(20))
    -> begin
    -> select * from FARE where site=place;
    -> end $$
Query OK, 0 rows affected (0.00 sec)

mysql> delimiter $$
mysql> call XCF0('nanjing');
    -> $$
+---------+-------+------------+
| site    | money | date       |
+---------+-------+------------+
| nanjing |  2000 | 2021-02-07 |
+---------+-------+------------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

mysql> delimiter ;

     
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MySQL database SQL High level use of statements （ Two ）_ character string _13

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
usage ：

DROP PROCEDURE IF EXISTS Proc;
# Delete... Only if it exists , If the specified procedure does not exist , Then there will be a mistake 

 example ：
drop procedure if exists XCF0;

     
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MySQL database SQL High level use of statements （ Two ）_mysql_14

8. Control statement of stored procedure

8.1 Conditional statements （if）

mysql> DELIMITER $$
mysql> CREATE PROCEDURE XCF1(IN num int(10))
    -> BEGIN
    -> declare var int;
    -> set var=num*2;
    -> if var>=10 then
    -> update FARE set money=money+1;
    -> else
    -> update FARE set money=money-1;
    -> end if;
    -> END $$
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;

     
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MySQL database SQL High level use of statements （ Two ）_ stored procedure _15

MySQL database SQL High level use of statements （ Two ）_ stored procedure _16

8.2 Loop statement （while）

mysql> create table xcf(id int(5));
Query OK, 0 rows affected (0.01 sec)

mysql> DELIMITER $$
mysql> CREATE PROCEDURE XCF2()
    -> BEGIN
    -> declare var int;
    -> set var=0;
    -> while var<9 do
    -> insert into xcf values(var);
    -> set var=var+1;
    -> end while;
    -> END $$
Query OK, 0 rows affected (0.00 sec)

mysql> CALL XCF2;
    -> $$
Query OK, 1 row affected (0.01 sec)

mysql> select * from xcf;
    -> $$
+------+
| id   |
+------+
|    0 |
|    1 |
|    2 |
|    3 |
|    4 |
|    5 |
|    6 |
|    7 |
|    8 |
+------+
9 rows in set (0.00 sec)


     
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