I had a very big excel spreadsheet that I moved into Access to try to deal with it easier. I'm very much a novice. I'm trying to use SQL via Access.
I need to assign a unique identifier to duplicates. I've seen people use DENSE_RANK in SQL but I can't get it to work in Access.
Here's what I'm trying to do: I have a large amount of patient and sample data (20k rows). My columns are called FULL_NAME, SAMPLE_NUM, and DATE_REC. Some patients have come in more than once and have multiple samples. I want to give each patient a unique ID that I want to call PATIENT_ID.
I can't figure out how to do this, aside from typing it out on each row. I would greatly appreciate help as I really don't know what I'm doing and there is no one at my work who can help.
To illustrate the previous answers' textual explanation, consider the following SQL action queries which can be run in an Access query window one by one or as VBA string queries with DAO's CurrentDb.Execute or DoCmd.RunSQL. The ALTER statements can be done in MSAcecss.exe.
Create a Patients table (make-table query)
SELECT DISTINCT s.FULL_NAME INTO myPatientsTable
FROM mySamplesTable s
WHERE s.FULL_NAME IS NOT NULL;
Add an autonumber field to new Patients table as a Primary Key
ALTER TABLE myPatientsTable ADD COLUMN PATIENT_ID AUTOINCREMENT NOT NULL PRIMARY KEY;
Add a blank Patient_ID column to Samples table
ALTER TABLE mySamplesTable ADD COLUMN PATIENT_ID INTEGER;
Update Patient_ID Column in Samples table using FULL_NAME field
UPDATE mySamplesTable s
INNER JOIN myPatientsTable p
ON s.[FULL_NAME] = p.[FULL_NAME]
SET s.PATIENT_ID = p.PATIENT_ID;
Maintain third-norm principles of relational databases and remove FULL_NAME field from Samples table
ALTER TABLE mySamplesTable DROP COLUMN FULL_NAME;
Then in a separate query, add a foreign key constraint on PATIENT_ID
ALTER TABLE mySamplesTable
ADD CONSTRAINT PatientRelationship
FOREIGN KEY (PATIENT_ID)
REFERENCES myPatientsTable (PATIENT_ID);
Sounds like FULL_NAME is currently the unique identifier. However, names make very poor unique identifiers and name parts should be in separate fields. Are you sure you don't have multiple patients with same name, e.g. John Smith?
You need a PatientInfo table and then the SampleData table. Do a query that pulls DISTINCT patient info (apparently this is only one field - FULL_NAME) and create a table that generates unique ID with autonumber field. Then build a query that joins tables on the two FULL_Name fields and updates a new field in SampleData called PatientID. Delete the FULL_Name field from SampleData.
The command to number rows in your table is [1]
ALTER TABLE MyTable ADD COLUMN ID AUTOINCREMENT;
Anyway as June7 pointed out it might not be a good idea to combine records just based on patient name as there might be duplicates. Better way will be treat each record as unique patient for now and have a way to fix patient ID when patient comes back. I would suggest to go this way:
create two new columns in your samples table
ID with autoincrement as per query above
patientID where you will copy values from ID column - for now they will be same. But in future they will diverge
copy columns patientID and patientName into separate table patients
now you can delete patientName column from samples table
add column imported to patients table to indicate, that there might be some other records that belong to this patient.
when patients come back you open his record, update all other info like address, phone, ... and look for all possible samples record that belong to him. If so, then fix patient id in those records.
Now you can switch imported indicator because this patient data are up to date.
After fixing patientID for samples records. You will end up with patients with no record in samples table. So you can go and delete them.
Unless you already have a natural key you will be corrupting this data when you run the distinct query and build a key from it. From your posting I would guess a natural key would be SAMPLE_NUM. Another problem is that if you roll up by last name you will almost certainly be combining different patients into one.
Imagine I have a table in an Oracle database with 3 columns, ID (PK), NAME and ACTIVE. If I wanted, for example, to have NAME and ACTIVE be unique together, I could easily do that. However, what I want is for NAME to be unique only when ACTIVE in that row is set to true (1). When ACTIVE is false (0), I want to be able to have an arbitrary number of rows with the same NAME (but different ID, of course). Is this possible to do?
Yes, in Oracle you can create a unique index with a CASE statement, in your case something like;
CREATE UNIQUE INDEX ix_uq ON test(
name,
CASE WHEN active = 0 THEN id ELSE 0 END
)
Since id is unique, we can have multiple rows with the same name as long as active=0 (since the uniqueness will be based on the (name,id)), while an active entry will check uniqueness on (name,0) which allows only a single active row per name.
An SQLfiddle to test with. Try to add a duplicate active entry, and it will not insert.
Here another possibility.
CREATE UNIQUE INDEX ix_uq ON test(decode(active,1,name,null))
With that, your index is the smallest possible because you don't need to index inactive values. It couls be usefull if your table began to be very big with juste small active values
I want to add something to a table (trigger?) so that, for exactly, exactly 1 row per ID has a specific value for a specific column. So that if a statement was run that makes this not the case, an exception would be thrown and the insert would be rolled back.
Let's take this schema.
ID Current Value
1 Y 0
1 N 0
1 N 2
2 Y 2
And the constraint I want is that for each ID, exactly one row has a current of 'Y'.
Therefore, these statements would not be executed and return an appropriate error:
insert into table values (1,'Y',1);
insert into table values (3,'N',2);
update table set current = 'N' where ID = 1;
I have two questions:
Is it a good idea to code this kind of constraint logic into your table, or is that best saved for the applications that manipulate the data? Why?
How can it be done? What kind of tool does oracle provide to create a constraint like this?
It's best if you can specify it in a declarative fashion (rather than procedurally, e.g. using triggers). Especially because triggers, without some kind of locking algorithm, will NOT work anyway due to concurrent sessions trying to insert/update the table at the same time.
In this instance, the simplest solution is a unique, function-based index, e.g.:
CREATE UNIQUE INDEX only_one_current ON thetable
(CASE WHEN Current = 'Y' THEN ID END);
The expression is NULL if Current = 'N', and all-NULL rows in an index are not stored, which means that the uniqueness constraint will only apply to rows where Current = 'Y'.
I think what you are looking for is just a unique constraint.
You can add it using below statement so that only unique combination of ID , Current can exist in table.
ALTER TABLE table_name add CONSTRAINT constraint_name UNIQUE (ID,Current);
I have a table with an IDENTITY column
[Id] int IDENTITY(1, 1) NOT NULL
After some rows beeing added/removed I end with gaps in Id values:
Id Name
---------
1 Tom
2 Bill
4 Kate
Is there an easy way to compress the values to
Id Name
---------
1 Tom
2 Bill
3 Kate
?
I would strongly recommend that you leave the identity values as they are.
if this ID column is used as a foreign key on another table, changing them will get complicated very quickly.
if there is some business logic where they must be sequential then add a new column ID_Display where you can update them using ROW_NUMBER() and keep them pretty for the end user. I never let end users see and/or dictate how I create/populate/store the data, and if they are bothering you about the IDs then show them some other data that looks like an ID but is not a FK or PK.
I think it's pretty easy to create a 2nd table with the same schema, import all the data (except for the identity column of course; let the 2nd table start renumbering) from the first table, drop the first table and rename the 2nd to the original name.
Easiness may be in question if you'd have a ton of FK relationships to rebuild with other tables etc.
Well as far as I know the only way you can is manually update the values by turning Identity insert on..but you should really avoid doning such a thing in first place..also if you truncate the table it will not have those gaps.
I cannot control the part which requires ID columns to be in sequence.
This sounds like there is program logic which assumes there are no gaps--correct?
I need this to keep two different databases in sync.
It's still not clear what you mean. If the actual values in the IDENTITY column are not meaningful (not used as foreign keys by other tables), you can just do this:
DELETE FROM db1.table
SELECT col1, col2, col3 /* leave out the IDENTITY column */
INTO db1.table FROM db2.table
What's the best way to store a linked list in a MySQL database so that inserts are simple (i.e. you don't have to re-index a bunch of stuff every time) and such that the list can easily be pulled out in order?
Using Adrian's solution, but instead of incrementing by 1, increment by 10 or even 100. Then insertions can be calculated at half of the difference of what you're inserting between without having to update everything below the insertion. Pick a number large enough to handle your average number of insertions - if its too small then you'll have to fall back to updating all rows with a higher position during an insertion.
create a table with two self referencing columns PreviousID and NextID. If the item is the first thing in the list PreviousID will be null, if it is the last, NextID will be null. The SQL will look something like this:
create table tblDummy
{
PKColumn int not null,
PreviousID int null,
DataColumn1 varchar(50) not null,
DataColumn2 varchar(50) not null,
DataColumn3 varchar(50) not null,
DataColumn4 varchar(50) not null,
DataColumn5 varchar(50) not null,
DataColumn6 varchar(50) not null,
DataColumn7 varchar(50) not null,
NextID int null
}
Store an integer column in your table called 'position'. Record a 0 for the first item in your list, a 1 for the second item, etc. Index that column in your database, and when you want to pull your values out, sort by that column.
alter table linked_list add column position integer not null default 0;
alter table linked_list add index position_index (position);
select * from linked_list order by position;
To insert a value at index 3, modify the positions of rows 3 and above, and then insert:
update linked_list set position = position + 1 where position >= 3;
insert into linked_list (my_value, position) values ("new value", 3);
A linked list can be stored using recursive pointers in the table. This is very much the same hierarchies are stored in Sql and this is using the recursive association pattern.
You can learn more about it here (Wayback Machine link).
I hope this helps.
The simplest option would be creating a table with a row per list item, a column for the item position, and columns for other data in the item. Then you can use ORDER BY on the position column to retrieve in the desired order.
create table linked_list
( list_id integer not null
, position integer not null
, data varchar(100) not null
);
alter table linked_list add primary key ( list_id, position );
To manipulate the list just update the position and then insert/delete records as needed. So to insert an item into list 1 at index 3:
begin transaction;
update linked_list set position = position + 1 where position >= 3 and list_id = 1;
insert into linked_list (list_id, position, data)
values (1, 3, "some data");
commit;
Since operations on the list can require multiple commands (eg an insert will require an INSERT and an UPDATE), ensure you always perform the commands within a transaction.
A variation of this simple option is to have position incrementing by some factor for each item, say 100, so that when you perform an INSERT you don't always need to renumber the position of the following elements. However, this requires a little more effort to work out when to increment the following elements, so you lose simplicity but gain performance if you will have many inserts.
Depending on your requirements other options might appeal, such as:
If you want to perform lots of manipulations on the list and not many retrievals you may prefer to have an ID column pointing to the next item in the list, instead of using a position column. Then you need to iterative logic in the retrieval of the list in order to get the items in order. This can be relatively easily implemented in a stored proc.
If you have many lists, a quick way to serialise and deserialise your list to text/binary, and you only ever want to store and retrieve the entire list, then store the entire list as a single value in a single column. Probably not what you're asking for here though.
This is something I've been trying to figure out for a while myself. The best way I've found so far is to create a single table for the linked list using the following format (this is pseudo code):
LinkedList(
key1,
information,
key2
)
key1 is the starting point. Key2 is a foreign key linking to itself in the next column. So your columns will link something link something like this
col1
key1 = 0,
information= 'hello'
key2 = 1
Key1 is primary key of col1. key2 is a foreign key leading to the key1 of col2
col2
key1 = 1,
information= 'wassup'
key2 = null
key2 from col2 is set to null because it doesn't point to anything
When you first enter a column in for the table, you'll need to make sure key2 is set to null or you'll get an error. After you enter the second column, you can go back and set key2 of the first column to the primary key of the second column.
This makes the best method to enter many entries at a time, then go back and set the foreign keys accordingly (or build a GUI that just does that for you)
Here's some actual code I've prepared (all actual code worked on MSSQL. You may want to do some research for the version of SQL you are using!):
createtable.sql
create table linkedlist00 (
key1 int primary key not null identity(1,1),
info varchar(10),
key2 int
)
register_foreign_key.sql
alter table dbo.linkedlist00
add foreign key (key2) references dbo.linkedlist00(key1)
*I put them into two seperate files, because it has to be done in two steps. MSSQL won't let you do it in one step, because the table doesn't exist yet for the foreign key to reference.
Linked List is especially powerful in one-to-many relationships. So if you've ever wanted to make an array of foreign keys? Well this is one way to do it! You can make a primary table that points to the first column in the linked-list table, and then instead of the "information" field, you can use a foreign key to the desired information table.
Example:
Let's say you have a Bureaucracy that keeps forms.
Let's say they have a table called file cabinet
FileCabinet(
Cabinet ID (pk)
Files ID (fk)
)
each column contains a primary key for the cabinet and a foreign key for the files. These files could be tax forms, health insurance papers, field trip permissions slips etc
Files(
Files ID (pk)
File ID (fk)
Next File ID (fk)
)
this serves as a container for the Files
File(
File ID (pk)
Information on the file
)
this is the specific file
There may be better ways to do this and there are, depending on your specific needs. The example just illustrates possible usage.
There are a few approaches I can think of right off, each with differing levels of complexity and flexibility. I'm assuming your goal is to preserve an order in retrieval, rather than requiring storage as an actual linked list.
The simplest method would be to assign an ordinal value to each record in the table (e.g. 1, 2, 3, ...). Then, when you retrieve the records, specify an order-by on the ordinal column to get them back in order.
This approach also allows you to retrieve the records without regard to membership in a list, but allows for membership in only one list, and may require an additional "list id" column to indicate to which list the record belongs.
An slightly more elaborate, but also more flexible approach would be to store information about membership in a list or lists in a separate table. The table would need 3 columns: The list id, the ordinal value, and a foreign key pointer to the data record. Under this approach, the underlying data knows nothing about its membership in lists, and can easily be included in multiple lists.
This post is old but still going to give my .02$. Updating every record in a table or record set sounds crazy to solve ordering. the amount of indexing also crazy, but it sounds like most have accepted it.
Crazy solution i came up with to reduce updates and indexing is to create two tables (and in most use cases you don's sort all records in just one table anyway). Table A to hold the records of the list being sorted and table B to group and hold a record of the order as a string. the order string represents an array that can be used to order the selected records either on the web server or browser layer of a webpage application.
Create Table A{
Id int primary key identity(1,1),
Data varchar(10) not null
B_Id int
}
Create Table B{
Id int primary key Identity(1,1),
GroupName varchat(10) not null,
Order varchar(max) null
}
The format of the order sting should be id, position and some separator to split() your string by. in the case of jQuery UI the .sortable('serialize') function outputs an order string for you that is POST friendly that includes the id and position of each record in the list.
The real magic is the way you choose to reorder the selected list using the saved ordering string. this will depend on the application you are building. here is an example again from jQuery to reorder the list of items: http://ovisdevelopment.com/oramincite/?p=155
https://dba.stackexchange.com/questions/46238/linked-list-in-sql-and-trees suggests a trick of using floating-point position column for fast inserts and ordering.
It also mentions specialized SQL Server 2014 hierarchyid feature.
I think its much simpler adding a created column of Datetime type and a position column of int, so now you can have duplicate positions, at the select statement use the order by position, created desc option and your list will be fetched in order.
Increment the SERIAL 'index' by 100, but manually add intermediate values with an 'index' equal to Prev+Next / 2. If you ever saturate the 100 rows, reorder the index back to 100s.
This should maintain sequence with primary index.
A list can be stored by having a column contain the offset (list index position) -- an insert in the middle is then incrementing all above the new parent and then doing an insert.
You could implement it like a double ended queue (deque) to support fast push/pop/delete(if oridnal is known) and retrieval you would have two data structures. One with the actual data and another with the number of elements added over the history of the key. Tradeoff: This method would be slower for any insert into the middle of the linked list O(n).
create table queue (
primary_key,
queue_key
ordinal,
data
)
You would have an index on queue_key+ordinal
You would also have another table which stores the number of rows EVER added to the queue...
create table queue_addcount (
primary_key,
add_count
)
When pushing a new item to either end of the queue (left or right) you would always increment the add_count.
If you push to the back you could set the ordinal...
ordinal = add_count + 1
If you push to the front you could set the ordinal...
ordinal = -(add_count + 1)
update
add_count = add_count + 1
This way you can delete anywhere in the queue/list and it would still return in order and you could also continue to push new items maintaining the order.
You could optionally rewrite the ordinal to avoid overflow if a lot of deletes have occurred.
You could also have an index on the ordinal to support fast ordered retrieval of the list.
If you want to support inserts into the middle you would need to find the ordinal which it needs to be insert at then insert with that ordinal. Then increment every ordinal by one following that insertion point. Also, increment the add_count as usual. If the ordinal is negative you could decrement all of the earlier ordinals to do fewer updates. This would be O(n)