I'm working in my school project and I want to make the id subject of any student incremented automatically as foreign key. I am showing you the example below as prototype, there are two tables, when I'm trying to insert data into the second table, I get an error (necessary to insert another field id of the table)
CREATE DATABASE database1;
USE database1;
CREATE TABLE table1
(
IdTable1 INT NOT NULL IDENTITY,
NOM VARCHAR(30),
PRIMARY KEY(IDMEDO)
);
--auto increment is working here
INSERT INTO table1
VALUES ('data1Table1'), ('data2Table1'), ('data3Table1');
--auto increment is working here just with the primary key
CREATE TABLE table2
(
IdTable2 INT not null IDENTITY,
IdTable1 INT,
dataTable2 varchar(30),
primary key(IdTable2),
constraint fk_tbl1 foreign key(IdTable1) references Table1
);
--necessary to add id field
INSERT INTO table2
VALUES ('data1Table2'), ('data2Table2'), ('data3Table2');
You should always (as a "best practice") define the columns you want to insert data into - that way, you can specify those that you have to provide values for, and let SQL Server handle the others. And for the foreign key, you have to explicitly provide a value - there's no "auto-magic" (or "auto-incrementing") way of associating a child row with its parent table - you have to provide the value in your INSERT statement.
So change your code to:
-- explicitly *specify* the NOM column here!
INSERT INTO table1 (NOM)
VALUES ('data1Table1'), ('data2Table1'), ('data3Table1');
-- again: explicitly *specify* the columns you want to insert into!
INSERT INTO table2 (IdTable1, dataTable2)
VALUES (1, 'data1Table2'), (2, 'data2Table2'), (3, 'data3Table2');
You need to insert the value of the foreign key wrt to table 1 now if you enter a value that's not in table 1 column which is acting as a foreign key then also it will not accept
Simply
Primary key and foreign key should match
Foreign key can't be null if table 1 doesn't contain a primary key with value null
Related
i'm trying and success to create primary key in Redshif
create table my_table(id int ,
primary key(id));
insert into my_table values
(id),
(1),
(1),
(20);
select count(*) from my_table
3
but it allows me to upload duplicated value ,
as far as i know primary key should contain unique values ,
did i do something wrong?
you can find your answer here
How to create an Index in Amazon Redshift
one of the answers mention your problem with the primary key
Create an identity key which will act as an auto_increment surrogate key. This'll serve both the purpose - to uniquely identify the records in the table and prevent insertion of duplicate values.
Let's create a dummy table:
create table scratchpad.test_1
(id bigint identity(1,1),
name varchar(10));
insert into scratchpad.test_1(name)
values
('a'),('b'),('c'),('d');
select * from scratchpad.test_1;
The id column acts as a primary key. Deleting any record from the table does not impact the sequencing of other values and the id column can be used to uniquely identify the subsequent row.
Why does add a foreign key to the tblDomare table result in this error?
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK__tblDomare__PersN__5F7E2DAC". The conflict occurred in database "almu0004", table "dbo.tblBana", column 'BanNR'.
Code
CREATE TABLE tblDomare
(PersNR VARCHAR (15) NOT NULL,
fNamn VARCHAR (15) NOT NULL,
eNamn VARCHAR (20) NOT NULL,
Erfarenhet VARCHAR (5),
PRIMARY KEY (PersNR));
INSERT INTO tblDomare (PersNR,fNamn,eNamn,Erfarenhet)
Values (6811034679,'Bengt','Carlberg',10);
INSERT INTO tblDomare (PersNR,fNamn,eNamn,Erfarenhet)
Values (7606091347,'Josefin','Backman',4);
INSERT INTO tblDomare (PersNR,fNamn,eNamn,Erfarenhet)
Values (8508284163,'Johanna','Backman',1);
CREATE TABLE tblBana
(BanNR VARCHAR (15) NOT NULL,
PRIMARY KEY (BanNR));
INSERT INTO tblBana (BanNR)
Values (1);
INSERT INTO tblBana (BanNR)
Values (2);
INSERT INTO tblBana (BanNR)
Values (3);
ALTER TABLE tblDomare
ADD FOREIGN KEY (PersNR)
REFERENCES tblBana(BanNR);
It occurred because you tried to create a foreign key from tblDomare.PersNR to tblBana.BanNR but/and the values in tblDomare.PersNR didn't match with any of the values in tblBana.BanNR. You cannot create a relation which violates referential integrity.
This query was very useful for me. It shows all values that don't have any matches
select FK_column from FK_table
WHERE FK_column NOT IN
(SELECT PK_column from PK_table)
Try this solution:
There is a data item in your table whose associated value doesn't exist in the table you want to use it as a primary key table.
Make your table empty or add the associated value to the second table.
It is possible to create the foreign key using ALTER TABLE tablename WITH NOCHECK ..., which will allow data that violates the foreign key.
"ALTER TABLE tablename WITH NOCHECK ..." option to add the FK -- This solution worked for me.
Remove all existing data from your tables and then make a relation between the tables.
Before You add Foreign key to the table, do the following
Make sure the table must empty or The column data should match.
Make sure it is not null.
If the table contains do not go to design and change, do it manually.
alter table Table 1 add foreign key (Column Name) references Table 2 (Column Name)
alter table Table 1 alter column Column Name attribute not null
I guess, a column value in a foreign key table should match with the column value of the primary key table. If we are trying to create a foreign key constraint between two tables where the value inside one column(going to be the foreign key) is different from the column value of the primary key table then it will throw the message.
So it is always recommended to insert only those values in the Foreign key column which are present in the Primary key table column.
For ex. If the Primary table column has values 1, 2, 3 and in Foreign key column the values inserted are different, then the query would not be executed as it expects the values to be between 1 & 3.
In very simple words your table already has data present in it and the table you are trying to create relationship with does have that Primary key set for the values that are already present.
Either delete all the values of the existing table.
Add all the values of foreign key reference in the new table.
Try DELETE the current datas from tblDomare.PersNR . Because the values in tblDomare.PersNR didn't match with any of the values in tblBana.BanNR.
When you define a Foreign Key in table B referencing the Primary Key of table A it means that when a value is in B, it must be in A. This is to prevent unconsistent modifications to the tables.
In your example, your tables contain:
tblDomare with PRIMARY KEY (PersNR):
PersNR |fNamn |eNamn |Erfarenhet
-----------|----------|-----------|----------
6811034679 |'Bengt' |'Carlberg' |10
7606091347 |'Josefin' |'Backman' |4
8508284163 |'Johanna' |'Backman' |1
---------------------------------------------
tblBana:
BanNR
-----
1
2
3
-----
This statement:
ALTER TABLE tblDomare
ADD FOREIGN KEY (PersNR)
REFERENCES tblBana(BanNR);
says that any line in tblDomare with key PersNR must have a correspondence in table tblBana on key BanNR. Your error is because you have lines inserted in tblDomare with no correspondence in tblBana.
2 solutions to fix your issue:
either add lines in tblBana with BanNR in (6811034679, 7606091347, 8508284163)
or remove all lines in tblDomare that have no correspondence in tblBana (but your table would be empty)
General advice: you should have the Foreign Key constraint before populating the tables. Foreign keys are here to prevent the user of the table from filling the tables with inconsistencies.
i had this error too
as Smutje reffered make sure that you have not a value in foreign key column of your base foreign key table that is not in your reference table i.e(every value in your base foreign key table(value of a column that is foreign key) must also be in your reference table column)
its good to empty your base foreign key table first then set foreign keys
the data you have entered a table(tbldomare) aren't match a data you have assigned primary key table. write between tbldomare and add this word (with nocheck) then execute your code.
for example you entered a table tbldomar this data
INSERT INTO tblDomare (PersNR,fNamn,eNamn,Erfarenhet)
Values (6811034679,'Bengt','Carlberg',10);
and you assigned a foreign key table to accept only 1,2,3.
you have two solutions one is delete the data you have entered a table then execute the code. another is write this word (with nocheck) put it between your table name and add
like this
ALTER TABLE tblDomare with nocheck
ADD FOREIGN KEY (PersNR)
REFERENCES tblBana(BanNR);
Smutje is correct and Chad HedgeCock offered a great layman's example.
Id like to build on Chad's example by offering a way to find/delete those records.
We will use Customer as the Parent and Order as the child. CustomerId is the common field.
select * from Order Child
left join Customer Parent on Child.CustomerId = Parent.CustomerId
where Parent.CustomerId is null
if you are reading this thread... you will get results. These are orphaned children. select * from Order Child
left join Customer Parent on Child.CustomerId = Parent.CustomerId
where Parent.CustomerId is null Note the row count in the bottom right.
Go verify w/ whomever you need to that you are going to delete these rows!
begin tran
delete Order
from Order Child
left join Customer Parent on Child.CustomerId = Parent.CustomerId
where Parent.CustomerId is null
Run the first bit.
Check that row count = what you expected
commit the tran
commit tran
Be careful. Someone's sloppy programming got you into this mess. Make sure you understand the why before you delete the orphans. Maybe the parent needs to be restored.
From our end, this is the scenario:
We have an existing table in the database with records.
Then I introduces a NOT nullable foreign key
After executing the update i got this error.
How did i solve you ask?
SOLUTION: I just removed all the records of the table, then tried to update the database and it was successful.
This happens to me, since I am designing my database, I notice that I change my seed on my main table, now the relational table has no foreign key on the main table.
So I need to truncate both tables, and it now works!
You should see if your tables has any data on the rows. If "yes" then you should truncate the table(s) or else you can make them to have the same number of data at tblDomare.PersNR to tblBana.BanNR and vise-verse.
In my scenario, using EF, upon trying to create this new Foreign Key on existing data, I was wrongly trying to populate the data (make the links) AFTER creating the foreign key.
The fix is to populate your data before creating the foreign key since it checks all of them to see if the links are indeed valid. So it couldn't possibly work if you haven't populated it yet.
I encounter some issue in my project.
In child table, there isn't any record Id equals 1 and 11
I inserted DEAL_ITEM_THIRD_PARTY_PO table which Id equals 1 and 11 then I can create FK
Please first delete data from that table and then run the migration again. You will get success
I had the same problem.
My issue was having nullable: true in column (migration file):
AddColumn("dbo.table", "column", c => c.Int(nullable: true));
Possible Solutions:
Change nullable 'false' to 'true'. (Not Recommended)
Change property type from int to int? (Recommended)
And if required, change this later after adding column > then missing field data in previous records
If you've changed an existing property from nullable to non-nullable:
3) Fill the column data in database records
A foreign key constraint in a child table must have a parent table with a primary key. The primary key must be unique. The foreign key value must match a value in the patent table primary key
When you alter table column from nullable to not nullable column where this column is foreign key, you must :
Firstly, initialize this column with value (because it is foreign
key not nullable).
After that you can alter your table column normally.
Please try below query:
CREATE TABLE tblBana
(BanNR VARCHAR (15) NOT NULL PRIMARY KEY,
);
CREATE TABLE tblDomare
(PersNR VARCHAR (15) NOT NULL PRIMARY KEY,
fNamn VARCHAR (15) NOT NULL,
eNamn VARCHAR (20) NOT NULL,
Erfarenhet VARCHAR (5),
FK_tblBana_Id VARCHAR (15) references tblBana (BanNR)
);
INSERT INTO tblBana (BanNR)
Values (3);
INSERT INTO tblDomare (PersNR,fNamn,eNamn,Erfarenhet,FK_tblBana_Id)
Values (8508284173,'Johanna','Backman',1,3);
or you can use this
SELECT fk_id FROM dbo.tableA
Except
SELECT fk_id From dbo.tableB
and just FYI, in case you do all of your data reference checks and find no bad data...apparently it is not possible to create a foreign key constraint between two tables and fields where those fields are the primary key in both tables! Do not ask me how I know this.
I tired to delete the occurrences of the values which the insert stmt was trying to insert
in the dependent table.
delete from BSC_UR_RE_AN
where AN_ID in (1084,1083,1088,1087,1121,1122,1123,1094,5010,
1239,1242,70187,7001,7002,1284,1285)
But no luck, I got the following error:
The INSERT statement conflicted with the FOREIGN KEY constraint
"BSC_U_RA_AN_FK". The conflict occurred in database "DMDB", table
"dbo.BSC_AN", column 'AN_ID'.
That error means that ANAG_ID value you're trying to insert as FOREIGN KEY doesn't exists on the related table. So, you should not delete it, you should insert it if it's missing.
Edit:
You should have a clear view of your tables design, examining the constraint of the tables you're trying to insert into.
As example, a Foreign Key constraint usually refers to a Primary Key of another table.
The error you see is because you're trying to inserd an invalid value (eg. not exists in the master table).
An example:
CREATE TABLE MasterTable (
ID int NOT NULL PRIMARY KEY,
Name varchar(50)
)
CREATE TABLE MasterTableValues (
IDMasterTable INT REFERENCES MasterTable(ID), --FOREIGN KEY
Value varchar(50)
)
Let's assume you have this data in MasterTable:
1 FirstDate
2 SecondData
3 ThirdData
5 FifthData
Now, you can insert these values in MasterTableValues:
1 SomeValue
1 SomeOtherValue
3 SomeValue
But CANNOT insert this value:
4 SomeValue
because the key ID = 4 don't exist in MasterTable
I'm about ready to rip my hair out on this one. I'm fairly new to MS SQL, and haven't seen a similar post anywhere.
When I try to do a statement like this:
INSERT INTO qcRawMatTestCharacteristic
VALUES(NULL, 1,1,1,1,1,1,1,'','','', GETDATE(), 1)
I get the following:
Cannot insert the value NULL into
column 'iRawMatTestCharacteristicId',
table
'Intranet.dbo.qcRawMatTestCharacteristic';
column does not allow nulls. INSERT
fails.
I understand the error, but the null value is for my my primary field with an int data type.
Any ideas!?
Primary keys in any relational database are not allowed to be NULL - it's one of the main, fundamental characteristics of a primary key.
See: SQL by Design: how to Choose the primary key
Never Null
No primary key value can be null, nor can you do anything to
render the primary key null. This is
an inviolate rule of the relational
model as supported by ANSI, of
relational database management system
(RDBMS) design, and of SQL Server.
UPDATE: ok, so you want an "auto-increment" primary key in SQL Server.
You need to define it as an INT IDENTITY in your CREATE TABLE statement:
CREATE TABLE dbo.YourTable(ID INT IDENTITY, col1 INT, ..., colN INT)
and then when you do an INSERT, you need to explicitly specify the columns to insert, but just don't specify the "ID" column in that list - then SQL Server will handle finding the proper value automagically:
INSERT INTO dbo.YourTable(col1, col2, ..., colN) -- anything **except** `ID`
VALUES(va1l, val2, ..., valN)
If you want to do this after having created the table already, you can do so in the SQL Server Management Studio's table designer:
Primary Key fields cannot contain null values in MS SQL. If you want to populate a SQL table and dont know what to enter for a integer based primary key field then set the pk to an Identity field. Also when specifying Insert statements its wise to use the column mapping portion of the insert statment for example:
Insert into (field1, field2, field3)
values
(value1, value2, value3)
The reason for this is it insures that the column order is what you developed for as a SQL administrator can modify column order. It also allows you to insert a row with an identity Primary key with out specifying the value of the Primary Key Example
CREATE TABLE [dbo].[foo](
[fooid] [int] IDENTITY(1,1) NOT NULL,
[name] [varchar](50) NULL,
CONSTRAINT [PK_foo] PRIMARY KEY
(
[fooid] ASC
)
now my insert statement is simple
Insert into foo (name)
values
("John")
the result in the table would be
1, "John"
You probably don't have (you forgot to add) autoincrement set on your integer primary key.
Primary keys shouldnt accept null value.Why you are inserting null values to a primary key field ?Primary key field should have a non-nullable,unique value which will make each of your record in the table unique
you can use 0 instead of null for only 1 unique row, null is not possible for PK. Or you can omit PK and use and auto increament PK field
Assuming you have an autoincrement field for your primary Key you'll need to include the field list on your insert and not put a value for that field e.g.
INSERT INTO qcRawMatTestCharacteristic
(Answer1,Answer2,...SomeDateField)
VALUES(1,1,1,1,1,1,1,'','','', GETDATE(), 1)
I'm assuming your real issue is that you're not sure how to write an insert statement so that the PK is auto populated correct? You need to name the fields you're setting values for, it looks like you're trying to set all of them but just exclude the PK field like so:
INSERT INTO someTable
(fieldName1, fieldName2)
VALUES(1,1)
Where sometable is a table with three fields. PK, fieldName1, and fieldName2. You also need to make sure that the identity property on the PK field is set to true.
if you have an identity column, you don't need to specify it in the insert statement.
INSERT INTO qcRawMatTestCharacteristic
VALUES(1,1,1,1,1,1,1,'','','', GETDATE(), 1)
However, if you have a primary key that isn't an identity column, then you do need to specify it, because otherwise it'll try to insert a null and primary keys by default are non-nullable.
I got an answer to another question here:
DB Schema For Chats?
It's a great answer, but I am not understanding the bit about references. I can do SQL statements but I have never used references.
What are they used for?
How are they used?
Give an example please
The REFERENCES keyword is part of a foreign key constraint and it causes MySQL to require that the value(s) in the specified column(s) of the referencing table are also present in the specified column(s) of the referenced table.
This prevents foreign keys from referencing ids that do not exist or were deleted, and it can optionally prevent you from deleting rows whilst they are still referenced.
A specific example is if every employee must belong to a department then you can add a foreign key constraint from employee.departmentid referencing department.id.
Run the following code to create two test tables tablea and tableb where the column a_id in tableb references the primary key of tablea. tablea is populated with a few rows.
CREATE TABLE tablea (
id INT PRIMARY KEY,
foo VARCHAR(100) NOT NULL
) Engine = InnoDB;
INSERT INTO tablea (id, foo) VALUES
(1, 'foo1'),
(2, 'foo2'),
(3, 'foo3');
CREATE TABLE tableb (
id INT PRIMARY KEY,
a_id INT NOT NULL,
bar VARCHAR(100) NOT NULL,
FOREIGN KEY fk_b_a_id (a_id) REFERENCES tablea (id)
) Engine = InnoDB;
Now try these commands:
INSERT INTO tableb (id, a_id, bar) VALUES (1, 2, 'bar1');
-- succeeds because there is a row in tablea with id 2
INSERT INTO tableb (id, a_id, bar) VALUES (2, 4, 'bar2');
-- fails because there is not a row in tablea with id 4
DELETE FROM tablea WHERE id = 1;
-- succeeds because there is no row in tableb which references this row
DELETE FROM tablea WHERE id = 2;
-- fails because there is a row in tableb which references this row
Important note: Both tables must be InnoDB tables or the constraint is ignored.
The REFERENCES keyword shows a foreign key constraint, which means that:
FOREIGN KEY (`chat_id` ) REFERENCES `chats`.`chat` (`id` )
...the chat_id column in the current table can only contain values that already exist in the chat table, id column.
For example, if the CHAT.id column contains:
id
----
a
b
c
..you can not add any values other than a/b/c into the chat_id column.