Update table to make primary key out of two foreign keys - sql

Have a table sample_tag which already exists with 1000's of entries.
It consists of two foreign keys, sample_id and tag_id.
However, the database is allowing duplicate sample_id/tag_id records to be created.
Without creating a new table, is there a SQL statement to update the sample_tag table such that the two foreign keys, together, function as its primary key?
Database is MySQL using phpMyAdmin

The main challenge is how you resolve the duplicates. If there are already duplicate keys, then you'll need to address these as a separate step (either deleting the duplicate, or merging any other columns as you see fit).
To check for duplicates, try:
SELECT sample_id, tag_id, COUNT( * )
FROM sample_tag
GROUP BY sample_id, tag_id;
If there are none, then you can go ahead and delete any existing primary key, and create a new one.

Related

There are no primary or candidate keys in the referenced table '' that match the referencing column

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

How can this SQL statement throw the following exception?

how can this statement:
DELETE FROM passage
WHERE passageid NOT IN
(
SELECT passageid from PreEndedPassages_passages
UNION SELECT fromPassageid from severalvisit
UNION SELECT toPassageid from severalvisit
UNION SELECT registerPassageid from stationobjects WHERE registerpassageid IS NOT NULL
UNION SELECT beginPassageid from stationobjects WHERE beginPassageid IS NOT NULL
UNION SELECT endPassageid from stationobjects WHERE endPassageid IS NOT NULL
)
throw this exception?
The DELETE statement conflicted with the FOREIGN KEY constraint "FK_statobj_begpasid". The conflict occurred in database "db.mdf", table "dbo.stationobjects", column 'beginpassageid'.
I have no clue, but it happened. beginPassageId is a foreign key on passageid.
EDIT:
Consider the NOT IN. I want to delete all passages that don't exist in one of its related tables. It usually works, but it happened once.
Thank you.
It means passage is parent table. and stationobjects is child table. You are trying to remove passageid from passage table which is present in stationobjects table as well.
First try to remove those passageid from stationobjects and then you can run this delete statement.
Alternate approach is cascade delete, if your DB supports that.
this kind of occur when you have a foreign key relationship in the two table.
This violates the Refrential Integrity .
so if you delete record from the primary table and record exist in foreign key table,
then you have two options:
1. either set the delete rule to cascade so that when ever you delete primary record the foreign key table record will get automatically deleted.
2.delete record from foreign key table first then from primary key table.
These kind of errors come up when table A foreign key is table B primary key and when you try to delete record in table A that has linking in table B, then deletion will not happen. Try dropping foreign key relation before delete. Same way truncate is used in tables by dropping fk relations and rebuilding them again after the table is reset

Insert into tables with primary and foreign key at same time

Very new to SQL and have spent a day on this already.
Here are my two tables:
Centre(cid, name, location, nurse_supervisor)
Nurse(nid, name, centre_id, certificate)
I have a big problem. The (nurse_supervisor) in Centre is a foreign key to Nurse (nid).
The (centre_id) in Nurse is a foreign key to (Centre cid).
I can't figure out how to populate these tables. I have tried:
INSERT ALL, which produces "A foreign key value has no matching primary key value"
I have tried removing the foreign key constraints and adding them after populating the tables but when I do that it says I can't add a constraint to tables with preexisting data.
I tried removing NOT NULL - but realized that was silly as the constraints will be enforced anyways.
Everything I look through says populate the parent table first and then the child, but these tables are linked to each other.
I am using SQL developer.
This is a poor schema design, but one way to get around it would be to:
Make both centre_id and nurse_supervisor columns NULL in the two table definitions
Insert all rows into both tables, but with NULL for those two columns
Update centre_id to the correct value for each row in the Nurse table
Update nurse_supervisor to the correct value for each row in the Centre table

Acquiring results from a foreign key reference

I am trying to set up a database that will hold/maintain a set of user privileges. I am also using Microsoft SQL Server Management Studio.
I have made a Accounts table, with the PK= UserId.
I have made a Profiles table with the PK=ProfileId
I Have made a UserPrivileges table using the following SQL statement
CREATE TABLE UserPermissions
(
UserId int REFERENCES Accounts (UserId),
ProfileId int REFERENCES Profiles (ProfileId),
PRIMARY KEY (UserId, ProfileId)
)
But when I execute a Select query from the UserPrivileges table, nothing is returned even though I do have a few entries in the 2 previous tables.
From my understanding of foreign keys, their values are taken from the referenced table. And since the referenced tables do have entries, why are none being entered into the UserPrivileges table?
A foreign key is just a reference. If doesn't mean that you don't need entries in your table. You need them! But these entries has also to exist in the related table. Here is a very good explanation: http://www.w3schools.com/sql/sql_foreignkey.asp
First, you didn't create a UserPrivileges table. You created a UserPermissions table. (If we're to believe your code.)
Second, no rows are being entered in UserPermissions because you didn't insert any rows into UserPermissions. Foreign keys don't make rows appear as if by magic. You decide which rows belong in UserPermissions, and you insert them.

SQL Server 2008: The columns in table do not match an existing primary key or unique constraint

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