Stored Functions in Mysql

1. Define variables

set variable name = variable value

Note: To distinguish between system variables and user-defined variables, add the @ symbol in front of user-defined variables

You can get the current variable through select

2. select into syntax to inject variable values

select a,b,c into @a,@b,@c syntax

If select returns a multi-line syntax, mysql will report an error or assign the last line

In sql total assignment, you can use @who :=xxx assignment

3. Built-in functions

format, Now, from_unixtime(), unix_timestamp(), charLength() are related to encoding, length()

concat，substring

The following defines several common types of custom functions

1. No parameter custom function

delimiter $$
create function sayHello() returns varchar(25)
begin
return 'Hello ShanShanBox.com';
end
$$
delimiter ;

Notice:

The function is bound to the database and can be accessed using the database name and method name

The function must have a return value, and returns must be added with S

2. With if logical judgment

delimiter $$
create function func1() returns varchar(5)
begin
if hour(now()) > 17 then
	return 'late';
else
	return 'early';
end if;
end
$$
delimiter ;

3. With a while loop function

delimiter $$
create function func2() returns int
begin
set @i = 1;
set @sum = 0;
while @i <= 10 do
	set @sum = @sum + @i;
	set @i = @i + 1;
end while;
return @sum;
end
$$
delimiter ;

4. Loop Control

leave is equivalent to break to terminate the loop

iterate is equivalent to continue, skipping the current loop for the next loop

In the while loop, the loop is not controlled according to the position of leave and iterate, but is determined by the label of the loop

So what is the label of the loop, in fact, I can't tell, just look at the code

delimiter $$
create function func3() returns int
begin
set @i = 1;
set @sum = 0;
w:while @i <= 10 do
	if @i = 5 then
	leave w;
	end if;
	set @sum = @sum + @i;
	set @i = @i + 1;
end while;
return @sum;
end
$$
delimiter ;

See, w: is the label of the while loop, what a beautiful expression

5. Custom functions with parameters

delimiter $$
create function func4(username varchar(20)) returns varchar(25)
begin
	return concat('hello ',username);
end
$$
delimiter ;

The above are a few simple custom functions

It's not easy to learn, do it and cherish it

Stored Functions in Mysql

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