Notes about First Database assignment

keep updating...

the script and document of this assignment can be downloaded fromClick to open the link

And here are notes about problems in this assignment:

Q2.

what format of data will it return if we compute two timestamp data?

so we know that, timestamp is shown as YYYY(year)MM(month)DD(day)HH(hour)MM(month)SS(second).

so if we compute (endTime - startTime) directly, the result will be (endTime(minute) - startTime(minute)) * 100 + (endTime(second) - endTime(second)).

so we should call time_to_sec to change this type of data to the type we want.

Q6.

Here, i'd like to discuss the usage of function.

this is the format of a simple function:

drop function if exists inZone1;
DELIMITER $$  
create function inZone1(id1 BIGINT UNSIGNED)
returns boolean
begin   
  if id1 in (select id from station where zone = 1)
  then return true;  
  else return false;
end if;
end $$

DELIMITER: In SQL we close each statement with a delimiter, which is always a semicolon (;). In a trigger we need to write multiple statements, each ending in a semicolon. To tell MySQL that those semicolons are not the end of our trigger statement, we should temporarily change the delimiter from ; to $$, so MySQL will know that the trigger statement only ends when it econunters a $$.

And the format of function is like this:

delimiter @@[we can use any signals]
create function [name of our function]([name of the parameter1] [type of the parameter1], ...)
returns [type of the return]
begin
statement1
...
end
end @@

In SQL you close each statement with a delimiter, which is by default a semicolon (;). In a trigger you need to write multiple statements, each ending in a semicolon. To tell MySQL that those semicolons are not the end of your trigger statement, you temporarily change the delimiter from ; to @@, so MySQL will know that the trigger statement only ends when it econunters a @@

Q10.

However, i met two problems when i solved this problem.

P1:

I want to select customer who have travel on line 0,1,2,3 , if one have journey on each line, he travels all the lines. In fact, line 0 should not be considered. But i thought that if one has journey that changes from one line to the other, he must have passed line 0. So, i wrote a function to find whether a journey crosses 2 lines:

DELIMITER $$  
create function isLastStation(id1 BIGINT UNSIGNED)
returns boolean
begin   
  if(id1 in (select id from station a
            where a.name != "City" and
            (a.id >= all(select id from station b
                               where a.line = b.line))))
  then return true;  
  else return false;
end if;
end $$

and the sql sequence is blow:

select username from customer c
where  (id in (select customer as customerOverLine1 from journey   //condition 1
            where  endStation in (select id from station
                                  where line = 1)
			or startStation in (select id from station
                                where line = 1)
			group by customer))
and (id in (select customer as customerOverLine2 from journey      //condition 2
            where  endStation in (select id from station
                                  where line = 2)
			or startStation in (select id from station
                                where line = 2)
			group by customer))
and (id in (select customer as customerOverLine3 from journey     //condition 3
            where  endStation in (select id from station
                                  where line = 3)
			or startStation in (select id from station
                                where line = 3)
			group by customer))

however, when i try to add

(id in (select customer as customerOverLine0 from journey
where! inSameLine (startStation, endStation)
group by customer))

the result is the carol only:

it's amazing that if i select id follow condition 2 and 3 and 4, there are four result: alice bob carol and dan; and if i select id follow condition 1 only, the result is alice bob carol dan and eve; but when i merge the conditions, there is only 1 result~

P2;

another problem arises when i tried to find another method to deal with the situation that i dont know the number of line and line id. so i have to write another function/procedure , deal with each line in table line. but the error 'missing end' cannot be solved ~ like pic below:

i want to set value to a variable parameter from a select sequence, but it always shows that i miss end after i set the value. if i add end, the body of function ends and another error arises...pity

Notes about First Database assignment

Guess you like