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MySQL advanced SQL statement 2

2022-07-02 04:00:00 【kiroct】

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];


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

 Intersection value -- Take two. SQL Intersection of statements 
SELECT A.Store_Name FROM location A INNER JOIN Store_Info B ON A.Store_Name = B.Sstore_Name;

SELECT A.Store_Name FROM location A INNER JOIN Store_Info B USING (Store_Name) ;

# One of the two tables has no specified row , And the other - This row of the table has repetition, which is not applicable , Use when two tables do have intersecting rows SELECT A.Store_Name FROM
(SELECT Store_Name FROM location UNION ALL SELECT Store_ Name FROM Store_Info) A
GROUP BY A. Store_Name HAVING COUNT(*) > 1;

# Take two. SQL The intersection of statement results , And there's no repetition 
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;

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;



 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 Store_Name FROM location WHERE (Store_ Name) NOT 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 NULL;

SELECT A.Store_Name FROM (SELECT DISTINCT Store_Name FROM location UNION ALL SELECT DISTINCT Store_Name FROM Store_ Info) A GROUP BY A.Store_Name HAVING COUNT(*) = 1;

     
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mysql senior SQL Sentence two _mysql High level statements

mysql senior SQL Sentence two _select Advanced application of statements _02

mysql senior SQL Sentence two _mysql High level statements _04

mysql senior SQL Sentence two _mysql High level statements _05

mysql senior SQL Sentence two _select Advanced application of statements _06

mysql senior SQL Sentence two _select Advanced application of statements _07

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mysql senior SQL Sentence two _mysql High level statements _10

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 .


SELECT Store_Name, CASE Store_Name
WHEN 'Los Angeles' THEN Sales * 2
WHEN   'Boston' THEN 1000
ELSE Sales
END
"New Sales", Date
FROM Store_Info;

#"New Sales"  Is used for CASE The field name of that field .


 Rank ：
 Form self linking (Self Join), Then list the results in order , Calculate each - Before line ( Including the line itself ) How many lines are there SELECT A1.Name, A1.Sales, COUNT (A2.Sales) Rank FROM Total Sales A1, Total Sales A2WHERE A1.Sales < A2.Sales OR (A1 .Sales=A2.Sales AND A1.Name = A2 . Name)GROUP BY A1.Name, A1.Sales ORDER BY A1.Sales DESC;
CREATE TABLE Total_Sales (Name char(10),Sales int(5));

INSERT INTO Total_Sales VALUES ('zhangsan',10);
INSERT INTO Total_Sales VALUES ('lisi',15);
INSERT INTO Total_Sales VALUES  ('wangwu',20);
INSERT INTO Total Sales VALUES  ('zhaoliu',40);

     
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mysql senior SQL Sentence two _mysql High level statements _11

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, Can't find out if it's worthless .
3. 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 .





SELECT length (NULL),length(''), length('1');
SELECT * FROM City WHERE name IS NULL;
SELECT * FROM City WHERE name IS NOT NULL;
SELECT * FROM City WHERE name = '';
SELECT * FROM City WHERE name <> ' ';
SELECT COUNT(*) FROM City; 
SELECT COUNT (name) FROM City;


     
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mysql senior SQL Sentence two _select Advanced application of statements _12 bold

mysql senior SQL Sentence two _select Advanced application of statements _13

Regular expressions

 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 '^[A-G]';
SELECT * FROM Store_Info WHERE Store_Name REGEXP 'Ho|Bo';

     
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mysql senior SQL Sentence two _mysql High level statements _14

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 :
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 

## 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 


## Calling stored procedure 
CALL Proc;

# 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 '%Proc8'] \G

## Parameters of stored procedure ##
IN Input parameters : Indicates that the caller passes a value... To the procedure ( The incoming value can be a word, a quantity, or a 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 )

DELIMITER $$
CREATE PROCEDURE Proc1 (IN inname CHAR(16))
-> BEGIN
-> SELECT * FROM Store_Info WHERE Store_Name = inname;
-> END $$
DELIMITER ;

CALL Proc1 ('Boston');


## 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    

## Control statement of stored procedure ##
create table t (id int(10));
insert into t values(10);

(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) ;


(2) Loop statement while .... end while
DELIMITER $$
CREATE PROCEDURE proc3 ()
-> begin
->declare var int (10);
->set var=0;
->while var<6 do
->insert into t values (var);
-> set var=var+1;
-> end while;
-> end $$
DELIMITER ;
CALL Proc3;



     
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summary ：

null  ''
regexp  ' Pattern '
 Associative intersection no intersection 

 stored procedure 
 establish : First modify the terminator temporarily ,create procedure  name () BEGIN .....   END Terminator recovery terminator is ;
call  The process of 

show create procedure  The process of 
show procedure status like  '...'

drop procedure The process of 
if ... then ... else ... end if
while ... do .... end while

     
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