I have created two tables in MySQL which are called "birthTable" and "deathTable". When I add a person in deathTable which she/he was in birthTable, I want to delete his/her name and family from birthtable because I add him/her in deathTable. But I don't know how I can do that?
What you describe can be done manually or with triggers, but generally you should not do it.
You should have a table called people, and then simply mark them as dead or alive. Instead, you may also create two columns for their birthday and deathday, if you intend to store this information.
In general, you shouldn't be moving records simply because some attribute about them has changed.
This is the SQL:
DELETE FROM birthTable WHERE id = ...
where id is the name of some identifying field.
Here is the documentation for DELETE.
What you have to do is construct a DELETE FROM-query. If you only want to delete one row from a table, you need to be certain that the parameters you give it are unique for that row. Usually this is done by having a column called id. Then, knowing the id, all you have to do is this:
DELETE FROM table WHERE id=<your id>;
I think that in your case you could just have a table called "people", and a boolean column "alive" which is 1 if the person is alive and 0 if the person is dead.
If you still want to delete one row from your birthTable, assuming you know the name of this person, you do it like this:
DELETE FROM birthTable WHERE firstName=<first name> AND lastName<last name>;
I've assumed that the column names for first and last names are firstName and lastName, you'll have to modify this to match your column names. This will delete any entry in the birthTable which matches the critera (could be more than one, if you have for example 2 people called Alan Johnson).
Hope that helps. :)
You can write trigger on insert on table deathTable which deletes corresponding row from birthTable.
CREATE TRIGGER trg_deathTable_insert
BEFORE INSERT ON deathTable
FOR EACH ROWS
BEGIN
DELETE FROM birthTable WHERE person_id = NEW.person_id;
END;
DELETE FROM birthTable WHERE id = xxx
Related
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.
I would like to have an sqlite table that maps names into unique IDs. I can create this table in the following way:
CREATE TABLE name_to_id (id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT)
With a select statement I can get the row containing a needed name and get from this row the corresponding ID.
The problem appears if I try to get ID for a name that is not yet in the table. The expected behavior in this case is that the new name will be added and its newly generated ID will be returned. I have two possible solutions/implementations of that.
The first solution is trivial:
We check if name is in the table.
If not we insert a row with the name.
We select the row with the name and read the needed ID from that row.
I do not like this solution because it can happen that the first process checks if the name in the table, it sees that the name is not there, meanwhile another process adds the name to the table and then the first process tries to add the same name.
The second solution seems to be better:
For any name we use insert if not exist.
We select from the table the row containing the name and get its ID.
Is the second solution optimal or there are better solutions?
The normal way to avoid duplicate entries in a table is to create an unique constraint. The database will then check for you if the record is already there and fail if so. That should be the best in terms of reliability and performance.
Next, the SQLite FAQ suggests to use the function last_insert_rowid() to fetch the ID instead of running a second query. This is actually the first question of the FAQ at all ;)
In pseudocode, the first solution looks like this:
cursor = db.execute("SELECT id FROM name_to_id WHERE name = ?", name)
if cursor.has_some_row:
id = cursor["id"]
else:
db.execute("INSERT INTO name_to_id(name) VALUES(?)", name)
id = db.last_insert_rowid
and the second like this:
db.execute("INSERT OR IGNORE INTO name_to_id(name) VALUES(?)", name)
cursor = db.execute("SELECT id FROM name_to_id WHERE name = ?", name)
id = cursor["id"]
The first solution requires a transaction around both commands, but this would be a good idea for the second solution, too, to avoid the overhead of multiple implicit transactions.
The second solution requires a unique constaint on name, but this would be a good idea for the first solution, too, for correctness and to speed up the name lookups.
Both solution use two SQL statements, and have similar speed.
(The second searches the row two times, but that data is cached.)
So there isn't anything obvious that makes one better that the other.
I am trying to delete a record in sqlite. i have four records record1, record2, record3, record 4
with id as Primary Key.
so it will auto increment for each record that i insert. now when i delete record 3, the primary key is not decrementing. what to do to decrement the id based on the records that i am deleting.
i want id to be 1,2,3 when i delete the record 3 from the database. now it is 1,2,4. Is there any sql query to change it. I tried this one
DELETE FROM TABLE_NAME WHERE name = ?
Note: I am implementing in xcode
I don't know why you want this but I would recommend leaving these IDs as is.
What is wrong with having IDs as 1,2,4?
Also you can potentially break things (referential integrity) if you use these ID values as foreign keys somewhere else.
Also please refer to this page to get a better understanding how autoincrement fields works
http://sqlite.org/autoinc.html
The sense of auto increment is always to create a new unique ID and not to fill the gaps created by deleting records.
EDIT
You can reach it by a special table design. There are no deleted records but with a field "del" marked as deleted.
For example, with a "select ... where del> 0" will find all active records.
Or place without the "where" all the records, then the ID's remain unaffected. To loop through an array with "if del = 0 continue". Thus, the array is always in consecutive order.
It's very flexible. Depending on the select ... you get.
all active records
all the deleted records
all records
I want to change the order of column e.g. name is first column of my table and there are 10 other columns in table I want to insert a new column in 2nd position after name column.
How is this possible?
1 - It's not possible without rebuilding the table, as Martin rightly points out.
2 - It's a good practice anyways to specify what fields you want and in what order in your SELECT statements as n8wrl points out.
3 - If you really really need a fixed order on your fields, could create a view that selects the fields you want in the order you want.
Like the rows in the table, there is no meaning to the order of the columns. In fact, it is best to specify the order you want the columns in your select statements rather than using select *, so you can 'insert' new columns wherever you want just by writing your SELECT statements accordingly.
Its possible to change the order. In some instances it really matters. have a personal experience.
Anyway..this query works fine.
ALTER TABLE user MODIFY Name VARCHAR(150) AFTER address;
You can achieve this by following these steps:
remove all foreign keys and primary key of the original table.
rename the original table.
using CTAS, create the original table in the order you want.
drop the old table.
apply all constraints back to the original table.
I have an access database that I need to update only if my information is unique. Is there a simple sql statement to accomplish this? Will 'insert ignore' work with access?
Example: I have the info stored in an array ('bob','34','hair'). If my database contains a record that matches on those three columns I would not want it to be inserted. If it was found to be unique I would like it to be inserted.
I am writing this in cold fusion but just cant seem to get the sql right.
Before doing an insert, do a select for those values. If you don't get a record back then you know it is safe to insert. Just use two separate queries, one for the check, and if no record found, then the insert.
A unique index is always a good idea if a field or set of fields should be unique. If you have a unique index in Access on the three fields, an insert will fail.
It is possible is to create a single query that only inserts a record where a matched record is not found, for example:
INSERT INTO Shows (ForeName,Reviews,Musical)
SELECT "bob" As ForeName,"34" As Reviews,"hair" As Musical
FROM (SELECT Count(*) As ExistsCount
FROM Shows
WHERE ForeName = "bob",Reviews = "34",Musical = "hair") AS e
WHERE e.ExistsCount=0