Database Management and High Availability Chapter 5 Database Functions and Database Creation Process

Database Management and High Availability Chapter 5 Database Functions and Database Creation Process

One: database functions

1.1: Mathematical functions

Mathematical function	description
abs(x)	Returns the absolute value of x	Absolute value
rand()	Returns a random number from 0 to 1	rand edge
mod (x, y)	Returns the remainder of x divided by y	Take the remainder
power (x, y)	Returns x to the power of y	power fast forward
round(x)	Returns the integer closest to x	round integer
round(x,y)	Keep the value of x after rounding to y decimal places
sqrt(x)	Returns the square root of x	sqrt square root
truncate(x,y)	Returns the value of the number x truncated to y decimal places	truncate interception
ceil(x)	Returns the smallest integer greater than or equal to x	Ceil mounted ceiling
floor(x)	Returns the largest integer less than or equal to x	floor
greatest(x1,x2...)	Returns the largest value in the collection
least(x1,x2...)	Return the smallest value in the set

1.2: Aggregate functions

Aggregate function	description
avg()	Returns the average value of the specified column	avg average
count()	Returns the number of non-NULL values ​​in the specified column	count count
min ()	Returns the minimum value of the specified column
max()	Returns the maximum value of the specified column
sum(x)	Returns the sum of all values ​​in the specified column

1.3: String functions

String function	description
length(x)	Returns the length of string x	length
trim()	Return the value without the specified format	trim trim, cut, remove spaces can only remove the spaces at both ends
concat(x,y)	Concatenate the provided parameters x and y into a string	concat merge
upper(x)	Change all letters of string x to uppercase letters	upper
lower(x)	Change all letters of string x to lowercase letters	lower
left(x,y)	Returns the first y characters of the string x	Value to the left
right(x,y)	Returns the last y characters of the string x	Value to the right
repeat (x, y)	Repeat string x y times	repeat repeat
space(x)	X spaces are returned	space space
replace(x,y,z)	Replace string z with string y in string x	replace
strcmp(x,y)	Comparing x and y, the returned value can be -1,0,1 and converted to ASCII code comparison	strcmp compares strings
substring(x,y,z)	Get a string of length z starting from the yth position in the string x	substring intercept string
reverse(x)	Reverse string x	reverse, reverse

1.4: Date and time functions

String function	description
curdate ()	Returns the year, month and day of the current time	Get the current date
curtime ()	Returns the hour, minute and second of the current time	Get current time
now()	Returns the date and time of the current time	What time is it now
month(x)	Returns the month value in date x
week(x)	Return date x is the first few weeks of the year
hour(x)	Returns the hour value in x
minute(x)	Returns the minute value in x
second(x)	Returns the seconds value in x
dayofweek (x)	Return x is the day of the week, 1 Sunday, 2 Monday
dayofmonth(x)	Calculation date x is the day of the month
dayofyear(x)	Calculation date x is the day of the year

1.5: Stored procedures

//Format
#define stored procedure

delimiter $$
create procedure存储过程名(in 参数名 参数类型)
begin
#定义变量
declare变量名变量类型
#变量赋值
set 变量名 = 值
sql语句1;
sql语句2;
..
sql语句n;
end $$
delimiter ;

#Call stored procedure
call stored procedure name (actual parameters);
#Query stored procedure
show procedure status where db='database';
#Delete stored procedure
drop procedure stored procedure name;

Example: 1

mysql> delimiter $$
mysql> create procedure myrole()                   //创建存储过程,名字为myrole
    -> begin
    -> select name,score from accp;
    -> end $$
Query OK, 0 rows affected (0.00 sec)

mysql> delimiter ;

mysql> call myrole();

Example: 2

mysql> delimiter $$
mysql> create procedure myschool(in my_name varchar(10))
    -> begin
    -> select name score from accp where name=my_name;
    -> end$$
Query OK, 0 rows affected (0.01 sec)

mysql> delimiter ;
mysql> show procedure status where db='school';

Example 3:

mysql> delimiter $$
mysql> create procedure myupdate(in my_score decimal(5,2))
  -> begin
    -> declare hob int(3);
    -> if my_score >= 80 then
    -> set hob = 1;
    -> else
    -> set hob = 2;
    -> end if;
    -> update accp set score=my_score,hobby=hob where name='zhangsan';
    -> end$$
Query OK, 0 rows affected (0.06 sec)
//修改名为张三的分数和hobby,修改zhangsan的hobby=2,score=75
mysql> delimiter ;
mysql> call myupdate(75);