I am having a simple scores table for HTML5 game with columns: name, email and score. Email value should be a unique value, but when the same users play the game again to better their scores, the score should be updated for that user. Now it returns an error because of the unique value. How should I create a table that will update the data?
The table I have created so far:
CREATE TABLE `scores` (
`id` INT NOT NULL AUTO_INCREMENT,
`name` VARCHAR( 20 ) NOT NULL,
`email` VARCHAR( 320 ) NOT NULL UNIQUE,
`score` INT NOT NULL,
PRIMARY KEY ( `id` )
) ENGINE = InnoDB;
You could use an insert statement with an on duplicate key clause:
INSERT INTO scores (name, email, score)
VALUES ('some_name', 'some_email', 123) -- Values from your application
ON DUPLICATE KEY UPDATE
score = CASE VALUES(score) > score THEN VALUES(score) ELSE score END
It is not about your create table query, it is about your insert query.
Use a try catch method to update the unique value
try
{
// inserting the line
}
catch (exception)
{
// Drop the row with that unique value
// inserting the same line which you have added in "try" section
}
Related
create table Hotel
(
hotel_id integer primary key NOT NULL,
hotel_name varchar(50) NOT NULL UNIQUE,
location_ varchar(50) NOT NULL,
rates varchar(10) check(rates in ('5star','4star','3star','2star','1star')),
);
create table Room
(
room_no integer primary key NOT NULL,
total_rooms integer NOT NULL,
room_price real check (room_price >= 0),
hotel_id integer foreign key references Hotel
);
insert into Hotel values(1,'sevensay','gamapaha','4star')
insert into Hotel values(2,'sarasvi','gamapaha','3star')
insert into Hotel values(3,'galadari','colombo','5star')
insert into Hotel values(4,'kingsbary','colombo','4star')
insert into Hotel values(5,'niramliii','gamapaha','5star')
insert into Hotel values(6,'sadalnka','kandy','3star')
insert into Hotel values(7,'sri lnkani','kandy','5star')
insert into Room values(100,10000,1)
insert into Room values(220,20000,2)
insert into Room values(160,1000,3)
insert into Room values(100,12000,4)
insert into Room values(50,15000,5)
insert into Room values(80,10000,6)
insert into Room values(100,20000,7)
drop table Room
drop table Hotel
select * from Hotel
select * from Room
create trigger rooms_availability
on Room
for insert
as
begin
declare #hotel_id integer
declare #total_rooms integer
select #hotel_id = hotel_id from inserted
select #total_rooms = count(*) from Room where hotel_id = #hotel_id
rollback transaction
if #total_rooms > 80
begin
print 'we have only 80 rooms .we cannot book the other rooms'
end
end
insert into Room values(300,10000,6)
How can I handle this error?
Msg 2627, Level 14, State 1, Line 25
Violation of PRIMARY KEY constraint 'PK__Room__1967F4191F8BEC00'. Cannot insert duplicate key in object 'dbo.Room'. The duplicate key value is (506).
The statement has been terminated.
The error you are showing is caused from trying to insert a row into Room with a duplicate primary key. However the code you provide doesn't have that error. And if you use an identity column (recommended for primary keys) you will never have that issue.
The more important issue is in your trigger, where you are not handling that fact that Inserted can have multiple rows. You can handle this correctly using a set based approach:
create trigger rooms_availability
on Room
for insert
as
begin
if exists (
select 1
from Room
where hotel_id in (select hotel_id from Inserted)
group by hotel_id
having count(*) > 80
)
begin
print 'We have only 80 rooms. We cannot book the other rooms.'
rollback;
end;
end
Note: I assume Print is being used for debugging. Once its working you will want to use throw.
I'm using database first approach with EF core and trying to figure out a clean solution to the below problem -
Consider a Student attendance table (irrelevant columns removed) below that stores date of class and allows the student to enter his class rating -
create table Student (
Id int Identity(1, 1) not null,
ClassDate smalldatetime not null,
ClassRatingByStudent varchar(250) not null
)
This is a webapp where school attendance system automatically populates the above table at EOD and then the student (let's say a few days later) is required to add class ratings. When the table is populated by the school attendance system, there is nothing in the ClassRatingByStudent column. Then when the student logs in, he must add the rating.
As you see, ClassRatingByStudent must be null when the school attendance system populates the table and must be not-null when the student saves his changes. One obvious solution is make ClassRatingByStudent column nullable ad handle it in the code but I'm wondering if there is a neater database (or maybe EF) level solution exists or some sort of pattern/architecture guidelines for this type of scenarios?
I don't know but maybe CHECK constraint could help you:
CREATE TABLE TestTable(
ID int NOT NULL IDENTITY,
RatingAllowed bit NOT NULL DEFAULT 0, -- switcher
RatingValue varchar(250),
CONSTRAINT PK_TestTable PRIMARY KEY(ID),
CONSTRAINT CK_TestTable_RatingValue CHECK( -- constraint
CASE
WHEN RatingAllowed=0 AND RatingValue IS NULL THEN 1
WHEN RatingAllowed=1 AND RatingValue IS NOT NULL THEN 1
ELSE 0
END=1
)
)
INSERT TestTable(RatingAllowed,RatingValue)VALUES(0,NULL)
INSERT TestTable(RatingAllowed,RatingValue)VALUES(1,'AAA')
-- The INSERT statement conflicted with the CHECK constraint "CK_TestTable_RatingValue"
INSERT TestTable(RatingAllowed,RatingValue)VALUES(0,'AAA')
INSERT TestTable(RatingAllowed,RatingValue)VALUES(1,NULL)
I found a variant how to check using another table as switcher
CREATE TABLE TableA(
ID int NOT NULL IDENTITY PRIMARY KEY,
StudentID int NOT NULL,
Grade int
)
CREATE TABLE TableB(
StudentID int NOT NULL PRIMARY KEY
)
GO
-- auxiliary function
CREATE FUNCTION GradeIsAllowed(#StudentID int)
RETURNS bit
BEGIN
DECLARE #Result bit=CASE WHEN EXISTS(SELECT * FROM TableB WHERE StudentID=#StudentID) THEN 1 ELSE 0 END
RETURN #Result
END
GO
-- constraint to check
ALTER TABLE TableA ADD CONSTRAINT CK_TableA_Grade CHECK(
CASE dbo.GradeIsAllowed(StudentID) -- then we can use the function here
WHEN 1 THEN CASE WHEN Grade IS NOT NULL THEN 1 ELSE 0 END
WHEN 0 THEN CASE WHEN Grade IS NULL THEN 1 ELSE 0 END
END=1)
GO
-- Tests
INSERT TableB(StudentID)VALUES(2) -- allowed student
INSERT TableA(StudentID,Grade)VALUES(1,NULL) -- OK
INSERT TableA(StudentID,Grade)VALUES(2,5) -- OK
INSERT TableA(StudentID,Grade)VALUES(1,4) -- Error
INSERT TableA(StudentID,Grade)VALUES(2,NULL) -- Error
INSERT TableB(StudentID)VALUES(1) -- add 1
UPDATE TableA SET Grade=4 WHERE StudentID=1 -- OK
UPDATE TableA SET Grade=NULL WHERE StudentID=1 -- Error
Table:
CREATE TABLE appointment
(
id bigserial NOT NULL,
date_of_visit timestamp without time zone NOT NULL,
symptoms text[],
diseases text[],
lab_tests text[],
prescription_id bigint NOT NULL,
medicines jsonb,
CONSTRAINT appointment_pkey PRIMARY KEY (id),
CONSTRAINT appointment_prescription_id_fkey FOREIGN KEY (prescription_id)
REFERENCES prescription (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
WITH (
OIDS=FALSE
);
Insert statement:
INSERT INTO appointment values(
1,
now(),
'{"abc","def","ghi"}',
'{"abc","def","ghi"}',
'{"abc","def","ghi"}',
1,
'[{"sku_id": 1, "company": "Magnafone"}, {"sku_id": 2, "company": "Magnafone"}]')
I am trying to query against a jsonb array type column in postgres. I had some solution in hand which is as below. Somehow it is not working The error is - Cannot extract elements from a scalar.
SELECT distinct(prescription_id)
FROM appointment
WHERE to_json(array(SELECT jsonb_array_elements(medicines) ->>'sku_id'))::jsonb ?|array['1']
LIMIT 2;
Update:
The query runs just fine. There was some unwanted value in the column for some other rows because of which it was not running.
There are rows in the table containing a scalar value in column medicines instead of array.
You should inspect and properly update the data. You can find these rows with this query:
select id, medicines
from appointment
where jsonb_typeof(medicines) <> 'array';
Alternatively, you can check the type of values in this column in the query:
select prescription_id
from (
select distinct on (prescription_id)
prescription_id,
case
when jsonb_typeof(medicines) = 'array' then jsonb_array_elements(medicines) ->>'sku_id'
else null
end as sku_id
from appointment
) alias
where sku_id = '1'
limit 2;
or simply exclude non-array values in where clause:
select prescription_id
from (
select distinct on (prescription_id)
prescription_id,
jsonb_array_elements(medicines) ->>'sku_id' as sku_id
from appointment
where jsonb_typeof(medicines) = 'array'
) alias
where sku_id = '1'
limit 2;
first of all: Thanks for all the great help I already received through finding answers to questions others posted.
I have a small and easy question for you:
I'm trying to randomly generate a number, but if it exists in the database table, it should keep generating a new numbers until it finds a unique number.
Help would be much appreciated!
$klantnr = rand(1,9);
$kn = mysql_num_rows(mysql_query('select username from users where id="'.$klantnr.'"'));
while($kn!=0){
$klantnr = rand(1,9);
}
echo $klantnr;
Create table with:
id integer primary key auto_increment
insert into users (id, username) values (NULL, 'name')
insert into users (username) values ('name')
MySQL will generate unique id for you
=== update
create table random_id (
id integer,
used tinyint,
primary key(id),
key idx_used(used)
);
for (0..9999) {
rand_id = get_random_id();
insert into random_id (id, used) values (rand_id, 0);
}
When need a random id, just fetch one from random_id table:
rand_id = select id from random_id where used = 0;
update random_id set used = 1 where id = :rand_id
use rand_id
Really it's pre generated random id, if you guarantee the users table's id only from random table, you doesn't need dealing with conflict ids :)
I know this is rather basic, and i've searched for answers for quite some time, but I'm troubled.
I don't know how to make my coding readable on here but here it is.
Here's the query for making the table in question:
CREATE TABLE customer
( customer_id INT NOT NULL CONSTRAINT customer_pk PRIMARY KEY IDENTITY,
first_name VARCHAR(20) NOT NULL,
surname VARCHAR(20) NOT NULL,
dob DATETIME NOT NULL,
home_address VARCHAR(50) NOT NULL,
contact_number VARCHAR(10) NOT NULL,
referrer_id INT NULL FOREIGN KEY REFERENCES customer(customer_id),
);
And here's the problem code:
--fill customer table
INSERT INTO customer
VALUES ( 'Harold', 'Kumar', '2010-07-07 14:03:54', '3 Blue Ln, Perth', 0812391245, NULL )
INSERT INTO customer
VALUES ( 'Bingo', 'Washisnameoh', '2010-09-21 12:30:07', '3 Red St, Perth', 0858239471, NULL )
INSERT INTO customer
VALUES ( 'John', 'Green', '2010-11-07 14:13:34', '4 Blue St, Perth', 0423904823, NULL )
INSERT INTO customer
VALUES ( 'Amir', 'Blumenfeld', '2010-11-01 11:03:04', '166 Yellow Rd, Perth', 0432058323, NULL)
INSERT INTO customer
VALUES ( 'Hank', 'Green', '2010-07-07 16:04:24', '444 Orange Crs, Perth', 0898412429, 8)
(Specifically the line with the 8 value at the end.)
When executing the second query it responds with this:
Msg 547, Level 16, State 0, Line 1
The INSERT statement conflicted
with the FOREIGN KEY SAME TABLE constraint
"FK_customer_referr__5772F790". The conflict occurred in database
"master", table "dbo.customer", column 'customer_id'. The statement
has been terminated.
Appreciate your help with this.
1)
You have a primary key on customer_id - and your insert statements do not have value for customer id
2)
You have a self referencing foreign key in the form of referrer_id referring to customer_id.
When you are inserting a record with referrer_id which is not null, in your case which is '8', make sure you already inserted a record with customer_id '8'
How do you know that the referrer_id is supposed to be 8 ??
What you need to do is catch the value of the customer_id inserted, and then used that in your second query:
DECLARE #referToID INT
INSERT INTO dbo.Customer(first_name, surname, dob, home_address, contact_number, referrer_id)
VALUES ('Harold', 'Kumar', '2010-07-07 14:03:54', '3 Blue Ln, Perth', 0812391245, NULL)
SELECT #ReferToID = SCOPE_IDENTITY() ; -- catch the newly given IDENTITY ID
INSERT INTO dbo.Customer(first_name, surname, dob, home_address, contact_number, referrer_id)
VALUES ('Hank', 'Green', '2010-07-07 16:04:24', '444 Orange Crs, Perth', 0898412429, #ReferToID)
I don't know which row you want to refer to (you didn't specify) - but I hope you understand the mechanism:
insert the new row into your table
get the newly inserted ID by using SCOPE_IDENTITY
insert the next row which refers to that first row and use that value returned by SCOPE_IDENTITY
Update: if you really want to have a given row reference itself (strange concept.....), then you'd need to do it in two steps:
insert the new row into your table
get the newly inserted ID by using SCOPE_IDENTITY
update that row to set the referrer_id
Something like this:
DECLARE #NewCustomerID INT
INSERT INTO dbo.Customer(first_name, surname, dob, home_address, contact_number)
VALUES ('Hank', 'Green', '2010-07-07 16:04:24', '444 Orange Crs, Perth', 0898412429)
SELECT #NewCustomerID = SCOPE_IDENTITY() ; -- catch the newly given IDENTITY ID
UPDATE dbo.Customer
SET referrer_id = #NewCustomerID
WHERE customer_id = #NewCustomerID
The only problem you have here is the identity must have a seed value which can be like Identity(1,1) where the first 1 is the starting point and the send 1 is the auto seed number...the re run your insert statement