I have a question. I have 2 tables and I want to inner join from left to right.
The left table contains a foreign key from the right table and it has his own primary key.
Should I join with the primary key + foreign key from the left table since I got the foreign key which has a connection to the right table?
Like for example
ON (left table primary key = left table foreign key)
But I can also use the left and the right table primary keys but what is then the different
ON (left table primary key = right table primary key)
In order to locate a row in a SQL table it needs to be uniquely identified by a primary key, this can be a numeric or string value and could use more than one field (a composite primary key).
When this information is used in a related table to reference the original row it is known as a foreign key. You do not need to combine the table's primary key with any foreign key that table holds in order to join the tables.
So you need a join where the left_table.foreign_key = right_table.primary_key
Without some table definitions and names of the actual fields you are using it's hard to give a more specific answer.
Related
How to delete records of a table when its primary key is referred as a foreign key in another table in a single query?
DELETE *
FROM table1
FULL OUTER JOIN table2 ON
table1.(Primary key column name) =table2.(Foreign key column name);
try this
I have a table that has a primary key voucher_no (varchar(10)) and I am trying to create a FK to this table/column from another new table but I am getting an error:
There are no primary or candidate keys in the referenced table 'apinv_hdr' that match the referencing column list in the foreign key 'fk_invoice_cfdi_x_voucher_apinv_hdr'
I have several other FK's tied to this table/column - why would it react this way now?
Primary Key and Foreign Key data types must match. Have you verified the column data types are the same?
Looks like some voucher_no record in another new table doesn't exist in voucher_no in main table.
Below script may help you.
select *
from another_new_table
where voucher_no not in (select voucher_no
from main_table)
If above query returns rows, you have two options:
delete those records from another_new_table or
insert records into main_table
This isn't a big deal, but my OCD is acting up with the following problem in the database I'm creating. I'm not used to working with databases, but the data has to be stored somewhere...
Problem
I have two tables A and B.
One of the datafields is common to both tables - segments. There's a finite number of segments, and I want to write queries that connect values from A to B through their segment values, very much asif the following table structure was used:
However, as you can see the table Segments is empty. There's nothing more I want to put into that table, rather than the ID to give other table as foreign keys. I want my tables to be as simple as possible, and therefore adding another one just seems wrong.
Note also that one of these tables (A, say) is actually master, in the sense that you should be able to put any value for segment into A, but B one should first check with A before inserting.
EDIT
I tried one of the answers below:
create table A(
id int primary key identity,
segment int not null
)
create table B(
id integer primary key identity,
segment int not null
)
--Andomar's suggestion
alter table B add constraint FK_B_SegmentID
foreign key (segment) references A(segment)
This produced the following error.
Maybe I was somehow unclear that segments is not-unique in A or B and can appear many times in both tables.
Msg 1776, Level 16, State 0, Line 11 There are no primary or candidate
keys in the referenced table 'A' that match the referencing column
list in the foreign key 'FK_B_SegmentID'. Msg 1750, Level 16, State 0,
Line 11 Could not create constraint. See previous errors.
You can create a foreign key relationship directly from B.SegmentID to A.SegmentID. There's no need for the extra table.
Update: If the SegmentIDs aren't unique in TableA, then you do need the extra table to store the segment IDs, and create foreign key relationships from both tables to this table. This however is not enough to enforce that all segment IDs in TableB also occur in TableA. You could instead use triggers.
You can ensure the segment exists in A with a foreign key:
alter table B add constraint FK_B_SegmentID
foreign key (SegmentID) references A(SegmentID)
To avoid rows in B without a segment at all, make B.SegmentID not nullable:
alter table B alter column SegmentID int not null
There is no need to create a Segments table unless you want to associate extra data with a SegmentID.
As Andomar and Mark Byers wrote, you don't have to create an extra table.
You can also CASCADE UPDATEs or DELETEs on the master. Be very carefull with ON DELETE CASCADE though!
For queries use a JOIN:
SELECT *
FROM A
JOIN B ON a.SegmentID = b.SegmentID
Edit:
You have to add a UNIQUE constraint on segment_id in the "master" table to avoid duplicates there, or else the foreign key is not possible. Like this:
ALTER TABLE A ADD CONSTRAINT UNQ_A_SegmentID UNIQUE (SegmentID);
If I've understood correctly, a given segment cannot be inserted into table B unless it has also been inserted into table A. In which case, table A should reference table Segments and table B should reference table A; it would be implicit that table B ultimately references table Segments (indirectly via table A) so an explicit reference is not required. This could be done using foreign keys (e.g. no triggers required).
Because table A has its own key I assume a given segment_ID can appear in table A more than once, therefore for B to be able to reference the segment_ID value in A then a superkey would need to be defined on the compound of A_ID and segment_ID. Here's a quick sketch:
CREATE TABLE Segments
(
segment_ID INTEGER NOT NULL UNIQUE
);
CREATE TABLE A
(
A_ID INTEGER NOT NULL UNIQUE,
segment_ID INTEGER NOT NULL
REFERENCES Segments (segment_ID),
A_data INTEGER NOT NULL,
UNIQUE (segment_ID, A_ID) -- superkey
);
CREATE TABLE B
(
B_ID INTEGER NOT NULL UNIQUE,
A_ID INTEGER NOT NULL,
segment_ID INTEGER NOT NULL,
FOREIGN KEY (segment_ID, A_ID)
REFERENCES A (segment_ID, A_ID),
B_data INTEGER NOT NULL
);
I am using SQL Server, and I need to add a foreign key to an already existing table.
The issue is the column which will act as the foreign key already has a few inconsistent values (which do not occur as a primary key) in another table.
I was wondering, when I alter the table and add the foreign key constraint, what will happen to the rows in the table with foreign key constraint , which has inconsistent values??
--Neeraj
In this case it is your decision. You can leave this values in table using WITH NOCHECK clause. But all new inserted values will be checked.
You'll get an error and nothing will be inserted.
To find all inconsistent rows (supposing that A and B are the target tables, A.id is a parent key and B.fk_id is a child, foreign key, id):
SELECT B.fk_id
FROM B
LEFT JOIN A ON A.id = B.fk_id
WHERE A.id IS NULL
After executing it you'll have all child rows that refers to "nowhere". So you either need to remove them, modify to point to the existing rows or set B.fk_id to NULL (if there is no NOT NULL constraint).
And after that query returns 0 rows - you can safely create foreign key constraint without any magic options.
I need to make some changes to a SQL Server 2008 database.
This requires the creation of a new table, and inserting a foreign key in the new table that references the Primary key of an already existing table. So I want to set up a relationship between my new tblTwo, which references the primary key of tblOne.
However when I tried to do this (through SQL Server Management Studio) I got the following error:
The columns in table 'tblOne' do not
match an existing primary key or
UNIQUE constraint
I'm not really sure what this means, and I was wondering if there was any way around it?
It means that the primary key in tblOne hasn't been properly declared - you need to go to tblOne and add the PRIMARY KEY constraint back onto it.
If you're sure that tblOne does have a PRIMARY KEY constraint, then maybe there are multiple tblOne tables in your DB, belonging to different schemas, and your references clause in your FK constraint is picking the wrong one.
If there's a composite key (which your comment would indicate), then you have to include both columns in your foreign key reference also. Note that a table can't have multiple primary keys - but if it has a composite key, you'll see a key symbol next to each column that is part of the primary key.
If you have a composite key the order is important when creating a FK, and sometimes the order is not how it is displayed.
What I do is go to the Keys section of the table1 and select script primary key as create to clipboard and then create FK using the order as shown in script
I've had this situation that led me to this topic. Same error but another cause. Maybe it will help someone.
Table1
ColA (PK)
ColB (PK)
ColC
Table2
ID (PK)
ColA
COLB
When trying to create foreign key in Table2 I've choose values from combobox in reverse order
Table1.ColB = Table2.ColB
Table1.ColA = Table2.ColA
This was throwing me an error like in topic name. Creating FK keeping order of columns in Primary key table as they are, made error disappear.
Stupid, but.. :)
If you still get that error after you have followed all advice from the above answers and everything looks right.
One way to fix it is by Removing your Primary keys for both tables, Save, Refresh, and add them again.
Then try to add your relationship again.
This Error happened with me When I tried to add foreign key constraint starting from PrimaryKey Table
Simpy go to other table and and create this foreign key constraint from there (foreign key Table)
This issue caught me out, I was adding the relationship on the wrong table. So if you're trying to add a relationship in table A to table B, try adding the relationship in table B to table A.
That looks like you are trying to create a foreign key in tblTwo that does not match (or participate) with any primary key or unique index in tblOne.
Check this link on MSDN regarding it. Here you have another link with a practical case.
EDIT:
Answwering to your comment, I understand you mean there are 2 fields in the primary key (which makes it a composite). In SQL it is not possible to have 2 primary keys on the same table.
IMHO, a foreign key field should always refer to a single register in the referenced table (i.e. the whole primary key in your case). That means you need to put both fields of the tblOne primary key in tblTwo before creating the foreign key.
Anyway, I have investigated a bit over the Internet and it seems SQL Server 2008 (as some prior versions and other RDBMS) gives you the possibility to reference only part of the primary key as long as this part is a candidate key (Not Null and Unique) and you create an unique constraint on it.
I am not sure you can use that in your case, but check this link for more information on it.
I have found that the column names must match.
Example:
So if tblOne has id called categoryId a reference in tblTwo must also be called categoryId.
_tblname, primary key name, foreign key_
tblOne, "categoryId", none
tblTwo, "exampleId", "categoryId"
I noticed this when trying to create foreign key between 2 tables that both had the column name "id" as primary key.
If nothing helps, then this could be the reason:
Considering this case:
Table A:
Column 1 (Primary Key)
Column 2 (Primary Key)
Column 3
Column 4
Table B:
Column a (Primary Key)
Column b
Column c
when you are defining a dependency B to A, then you are forced to respect the order in which the primaries are defined.
That's mean your dependency should look like this:
Table A Table B
Column 1 Column b
Column 2 Column c
AND NOT:
Table A Table B
Column 2 Column c
Column 1 Column b
then this will lead to the error you are encountering.
I've found another way to get this error. This can also happen if you are trying to make a recursive foreign key (a foreign key to the primary key in the same table) in design view in SQL Management Studio. If you haven't yet saved the table with the primary key it will return this message. Simply save the table then it will allow you to create the foreign key.
If you have data in your tables this could be the issue.
In my case I had some data in the Account table that I loaded at 3 pm, and some data in Contact table that I loaded at 3:10 pm, so Contact table had some values that weren't in my Account table yet.
I ended up deleting these values from the contact table and then managed to add a key without any problems.
Kindly also see that there are no existing data inside the table where the primary key is defined while setting the foreign key with another table column.
this was the cause of the error in my case.
I had to take backup empty the table set the relationship and then upload the data back.
sharing my experience
Was using ms sql smss