Easy to forget SQL statements

Me is the name of the index
ALTER  TABLE product add index   me(fuck)

- delete columns
ALTER  TABLE product DROP  fuck

- increase the column
ALTER  TABLE product add  fuck1 int NOT NULL

- explaining
EXPLAIN  SELECT * FROM product where id =1
-- Simple query both are the same
select * FROM users where gender="Male"GROUP BY school
select * FROM users GROUP BY school HAVING gender='male'

-- SELECT CONCAT(RTRIM(title),RTRIM(price)) FROM item
-- SELECT (price*10) AS p FROM item 
-- SELECT AVG(price) AS p,AVG(sales)as s from item WHERE price>90
SELECT sum(score)+ avg(score)AS f FROM student GROUP BY class

--is null left join
select Employee.name,Bonus.bonus from Employee left join Bonus on Employee.empId =Bonus.empId 
where bonus is null or bonus <1000 

-- Get the maximum number of orders
SELECT  customer_number   FROM orders GROUP BY customer_number ORDER BY COUNT(*) DESC LIMIT 1
Return either a or B in a table
SELECT distinct b.seat_id FROM cinema a,cinema  b
WHERE a.free=1 and b.free=1 and(
a.seat_id = b.seat_id - 1 
or
a.seat_id =b.seat_id +1 
)
order by b.seat_id

-- Use min function in grouping
SELECT player_id ,MIN(event_date)as first_login FROM Activity 	GROUP BYDevice_id string A="abvvv";
String b="abvvv"; As long as it's a String once you generate one the other one is the same String A="abvvv";

String b=newString("abvvv"); These two things are definitely different as long as you assign a value to a String, you have String A in the String constant pool=new String("ab");

String b="ab";
String c="ab";
System.out.println(b==c); The answer istrue
 

String a=new String("ab")+newString("vvv");; It's all about combining stringsfalse

String b=new String("abvvv");
;

   System.out.println(a==b); The answer isfalse
   

String b=new String("abvvv");
String a= "ab".concat("vvv");
falseAll the splices are flaseCopy the code