I have table 'students' with 'ID, name, surname, <...>, class' columns.
I have students
1, Michael, Jordan, <...>, A
and
2, Dikembe, Mutombo, <...>, B
How can I duplicate the existing table data for all the students with class value set to B, but change the class to C.
IDs have auto_increment enabled.
EDIT: Also, is it possible to do this without explicitly typing all column names?
Here's how you do that:
INSERT INTO tableA
(name, username, ..., class)
SELECT name, username, ..., B
FROM tableA
So if you don't want to type all the columns names you could run the above query but with '*' so you copy all values, then get the ID of the first element and run an update query from that ID on wards to update the class value.
Or have look at something like this, which in my opinion sounds a lot more complicated than typing it all out.
Hope you find a solution mate.
Related
So I have the following hierarchical database structure:
Table person has columns id and some other fields.
Table car has columns id, owner (with a foreign key constraint to person.id) and some other field
Table bumpersticker has columns id, car (with a foreign key constraint to car.id) and some other fields
I want to INSERT a row in to bumpersticker and have values to populate the row. I also have a person.id value of the person trying to add the bumpersticker.
What is the best practice to ensure that the car.owner value selected from the bumpersticker.car is in fact the same person.id as I have?
I guess one obvious way is to first execute a select query, on the car table and select the car.owner and validate that this value is the same value as the id of the person trying to add the bumpersticker and then execute an insert query.
but this seems like something there must be an elegant solution to in MySQL. at least not having to do two separate queries.
Most thankful for your help!
You can insert from a SELECT query that tests if the owner matches the criteria
INSERT INTO bumpersticker (car, sticker_text)
SELECT c.id, "If you can read this you're too close"
FROM car AS c
WHERE c.id = #car_id AND c.owner = #person_id
#car_id is the ID of the car you're adding the bumpersticker for, and #person_id is the ID of the user doing the insert. If the owner ID doesn't match, the SELECT query will return no rows, so nothing gets inserted.
DEMO
I have a table with a field (Name) I'd like to create a unique index on, however it seems there are existing duplicates. I dont' want to just get rid of dupes since some might have information in other fields that I need. Essentially I have:
ID
ParentID
Name
Code
RelatedID
So Goal 1 is I want to keep the record that has values in the secondary fields other then ID and Name. In most cases this will be one of the dupes only.
Goal 2 is in case two identical Names both have values but in different fields I want to 'merge' those since it is remotely possible one duplicate will have values in one key field and one in the other.
Finally Goal 3 is in the case that two names both have values in a key field I'd probably want to manually review those first.
It seems to me my first step as I read this would be Goal 3; manually review duplicates where Name Field is identical, and more then one record has a non-Null/non-empty value in a key field.
Once I address this the goal would be to 'mere' the remaining records i.e keep one record with Name and any non-null/non-empty key fields from the others.
Any thoughts much appreciated.
Sounds like a solid plan - hope you have a development environment you can dry run it in.
Here is some code that may help you along
Starting with Step 3.
This statement should help you find which records need to be reviewed.
SELECT *
FROM (
SELECT name,
GROUP_CONCAT(DISTINCT parentID) AS parentID,
GROUP_CONCAT(DISTINCT code) AS code,
GROUP_CONCAT(DISTINCT RelatedID) AS RelatedID,
FROM foo
GROUP BY name
HAVING COUNT(*)>1) as summarized
WHERE parentID LIKE '%,%'
OR code LIKE '%,%'
OR RelatedID LIKE '%,%';
Anything that comes up in that query you will probably have to manually fix after figuring out why there are multiple values for the same field.
Once those fixes are in place, it's times for the merge. I would create a holding / temporary table with the correct values. MAX should take care of the logic to choose non-null values
CREATE TABLE foo_values
SELECT name, MAX(parentID) as parentID, MAX(code) AS code, MAX(RelatedID) AS RelatedID.
FROM foo
GROUP BY name
HAVING COUNT(*)>1;
In theory, now you have the merged values. You can remove the duplicate name rows using whatever technique you are most comfortable with(See here) while adding your unique index. Finally, update the secondary fields by JOINing back to foo values.
I have a MySql table called Person, and one day I accidentally deleted someone from this table. I have a backup table, called PersonBak so I was going to restore my deletion from the backup. However, in the course of moving forward on my application I renamed all the fields in Person, except for the primary key, PersonID. Now Person and PersonBak have the same data, but only one matching column name.
Is there any way to restore my missing person to Person from PersonBak without doing a lot of work? I have quite a few columns. Of course I could just do the work now, but I can imagine this coming up again.
Is there some way to tell MySql that these are really the same table, with the columns in the same order, just different column names? Or any way at all to do this without writing out specifics of which columns in PersonBak match which ones in Person?
If the column datatypes are the same between the tables, the column count is the same, and they are all in the same order, then MySQL will do all of the work for you:
INSERT INTO t1 SELECT * FROM t2;
The column names are ignored. The server uses ordinal position only, to decide how to line up the from/to columns.
What about this:
insert into Person(id, col11, col12) (select id, col21, col22 from personBak where id=5)
person schema:
columns (id, col11, col12)
personBak schema:
columns (id, col21, col22)
Look at Mysql SELECT INTO and you can specify the field names & create an insert statement
I need to add data to a MySQL database like that:
Person:
pId, nameId, titleId, age
Name:
nameId, name
Title:
titleId, title
I don't want to have any names or title more then once in the db so I didn't see a solution with LAST_INSERT_ID()
My approach looks like that:
INSERT IGNORE INTO Name(name) VALUES ("Peter");
INSERT IGNORE INTO Title(title) VALUES ("Astronaut");
INSERT INTO Person(nameId, titleId, age) VALUES ((SELECT nameId FROM Name WHERE name = "Peter"), (SELECT nameId FROM Name WHERE name = "Astronaut"), 33);
But I guess that's a quite dirty approach!?
If possible I want to add multiple persons with one query and without having anything more then one times in db.
Is this possible in a nice way? Thanks!
You could put title and name as two columns of your table and then:
set one UNIQUE index on each column if you don"t want to have two titles or two names identical in the DB
or set an UNIQUE index on (title,name) if you don't want to have two entries having both the same name and the same title.
If you really want to have separate tables, you could do as you suggested in your post, but wrapping all your insert statements in a TRANSACTION to allow rollback if you detect a duplicate somewhere.
See Design dilemma: If e-mail address already used, send e-mail "e-mail address already registered", but can't because can't add duplicate to table which appear to be exactly the same problem, but having name & email instead of name & titles.
START TRANSACTION;
INSERT INTO title(value) VALUES ("Prof.");
SELECT LAST_INSERT_ID() INTO #title_id;
-- Instead of using user-defined variable,
-- you should be able to use the last_insert_id
-- equivalent from the host language MySQL driver.
INSERT INTO username(value) VALUES ("Sylvain");
SELECT LAST_INSERT_ID() INTO #username_id;
-- Instead of using user-defined variable,
-- you should be able to use the last_insert_id
-- equivalent from the host language MySQL driver.
INSERT INTO account(username_id, email_id) VALUES (#username_id,#title_id);
COMMIT;
See LAST_INSERT_ID()
A third solution would be to SELECT before doing you insert to see in the entry are already present. But personally I wouldn't push to the check-before-set approach at the very least, this will require an extra query which is mostly superfluous if you use correctly indexes.
Basically, I have two tables: images and servers. When I want to insert a row into the images table, I need to specify a s_id as one of the fields. Problem is, I only have name, which is another field in the servers table. I need to find what s_id belongs to name, and then use that in my INSERT INTO query on the images table.
Maybe this image will help:
http://i.imgur.com/rYXbW.png
I only know the name field from the servers table, and I need to use it to get the s_id field from the servers table. When I have that, I can use it in my INSERT INTO query, as it's a foreign key.
I found this:
http://www.1keydata.com/sql/sqlinsert.html
But it just confused me even more.
One solution would be to run two queries. One to get the s_id, and one to run the insert query. But I'd like to limit the amount of queries I run if there's a reasonable alternative.
Thanks!
You can use the INSERT ... SELECT form, something like this (with real column names and values of course):
INSERT INTO images (s_id, u_id, name, filename, uploaded)
SELECT s_id, ...
FROM servers
WHERE name = 'the name'
I don't know where you're getting the u_id, name, filename, or uploaded column values for images but you can include them as literal values in the SELECT:
INSERT INTO images (s_id, u_id, name, filename, uploaded)
SELECT s_id, 11, 'pancakes', 'pancakes.jpg', '2011-05-28 11:23:42'
FROM servers
WHERE name = 'the name'
This sort of thing will insert multiple values if servers.name is not unique.
You should be able to do something like this, but you'll need to fill in the items in <> with the values you want to insert.
INSERT INTO images (s_id, u_id, name, filename, uploaded)
(SELECT s_id, <u_id>, <name>, <filename>, <uploaded>
FROM imgstore.servers
WHERE name = #server_name)
This is the syntax for SQL Server, but I think it will work with MySQL as well.
Here's an article on INSERT ... SELECT Syntax
Please see my comment above regarding a potential data integrity issue. I am assuming that the name field in your server table has a unique constraint placed on it.
There are a couple of ways that you can approach this INSERT, and I'm sure that some are better than others. I make no claim that my way is the best way, but it should work. I don't know how you're writing this query, so I'm going to use #FieldValue to represent the variable input. My approach is to use a subquery in your insert statement to get the data that you require.
INSERT INTO images (field1, field2... s_id) VALUES ('#field1val', '#field2val'... (SELECT s_id FROM servers WHERE name='#nameval'));