I have inherited a company database which issues an order number as a GUID. Not exactly user friendly when you want to quote your order number! So what I want to do is add a new int column and add a unique sequential order number to each existing order (which has been ordered by datetime).
It's a great idea, but I'm stuck on how to actually do it as an update query! Any help would be greatly appreciated.
Add an identity column to your table and the numbering will be taken care of for you.
alter table YourTable add YourTableID int identity
One way.
alter table t add order_id int identity
This will add an auto-incrementing int identity column. There is no guarantee as to the order in which the ids will be assigned to the existing rows, but a unique id will be assigned to each existing row. Each new row inserted after this change will get a new unique id.
Before applying this to a real application consider whether existing code will work with an identity column. Often this approach is a really harmless upgrade. Code that tries to insert an identity column fails, unless it uses set identity_insert. You can't remove the identity property without dropping the column.
To round this out might want a unique constraint on the new id, both for retrieval speed and to enforce uniqueness if the id column is ever updated.
Unfortunately if you just add an IDENTITY column to the table, the existing orders will not necessarily get the IDENTITY values assigned in order of the OrderDate, so they will be "out of order" if you wanted to assign order ID values based on order date (which seems logical). Quick example:
CREATE TABLE dbo.Orders
(
OrderGUID UNIQUEIDENTIFIER DEFAULT NEWID() PRIMARY KEY,
OrderDate DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
);
INSERT dbo.Orders(OrderDate) VALUES
('20120101'), ('20120102'), ('20120103');
GO
ALTER TABLE dbo.Orders ADD OrderID INT IDENTITY(1,1);
GO
SELECT OrderID, OrderGUID, OrderDate = CONVERT(DATE, OrderDate)
FROM dbo.Orders
ORDER BY OrderDate;
Results (obviously yours will differ):
OrderID OrderGUID OrderDate
------- ------------------------------------ ----------
2 C5CE909E-0469-45AE-A828-647C7F54AA14 2012-01-01
1 70D8EEB1-FDA8-4E56-874F-771999C6DB84 2012-01-02
3 8E7B42C3-6C4D-4860-8A82-AFADDBA96A4A 2012-01-03
If this is not acceptable you should probably create a new table and insert all the old orders into it (at which point you can also drop the GUID column as I alluded to in my comment).
CREATE TABLE dbo.OrdersCopy
(
OrderID INT IDENTITY(1,1) PRIMARY KEY,
... other columns ...
);
INSERT dbo.OrdersCopy (OrderDate, ... other columns ...)
SELECT OrderDate, ... other columns ...
FROM dbo.Orders
ORDER BY OrderDate
OPTION (MAXDOP 1); -- single-threaded is important!
EXEC sp_rename 'dbo.Orders', 'OrdersOld', 'OBJECT';
EXEC sp_rename 'dbo.OrdersCopy', 'Orders', 'OBJECT';
(If you want to keep the old GUID for reference, temporarily, while you clean up other tables, that's probably fine, but you shouldn't make it auto-populate anymore, and you should plan to remove it since it's wide and redundant.)
Related
So For example. I have 1 table
and the name of the table is Suppliers
Contains :
1. SupplierName
2. SupplierID
I want to create another new table name Contracts
which contain new columns for
1. ContractID (new column)
2. SupplierID(from "Suppliers" table)
3. ContractValue (new column)
How do i do it?
I have researched and most of them told me to use Create table and then select, But it wont work and also ive tried alter table but still not working.
CREATE TABLE Contracts (
ContractID INT NOT NULL,
SELECT SupplierID
FROM Suppliers,
ContractValue INT NOT NULL,
ContractStart DATE NOT NULL)
These codes are not working so I'm not sure what is the solution.
CREATE TABLE Contracts (
ContractID INT NOT NULL,
(SELECT SupplierID
FROM Suppliers),
ContractValue INT NOT NULL,
ContractStart DATE NOT NULL)
I expect the result to be new table with ContractID (new column), SupplierID (from table Suppliers) and another new column named ContractValue
Think of Select query result set as a table or data grid.
So "SELECT [some fields] FROM [some table]" returns data grid where each row contains some fields from the table.
Therefore you can define table as select query with data OR alternatively specify the structure and create empty table. Most likely you don't want to mix those two approaches.
In your case, SupplierID field of contract table is a reference to SupplierID of Supplier table. In SQL it's called "foreign key". Theoretically you can use select statement in order to create new table and when you play a lot with database queries, you'll choose most convenient and faster way depending on your needs.
But when you start learning, it's better to create an empty table with structure and then insert data using new fields and existing data for the foreign key.
Therefore, the query will be something like:
CREATE TABLE Contracts (
ContractID INT NOT NULL,
SupplierID INT NOT NULL,
ContractValue INT,
ContractStart DATE
);
And then you can insert data using existing values from supplier table:
INSERT INTO Contracts (SupplierID)
SELECT SupplierID FROM Suppliers
Of course this is very simplified description
First, you have to specify ContractID as primary key. Then the query above will work only if you specify primary key as auto increment value, otherwise you have to use some logic and specify it explicitly.
In addition you have to specify default values if you want to use NOT NULL fields.
You can also specify SupplierID as foreign key, so only existing values will be added and some other integrity relationships will be supported.
See any MySQL or SQL documentation for details.
I don't know whether the below way could solve your problem
Make a copy of Suppliers table
Delete unnecessary column from the copied table
Add new column that you want to it.
You can use CTAS command.
CREATE TABLE Contracts as
SELECT
0 as ContractID,
SupplierID,
0 as ContractValue,
now() as ContractStart
FROM Suppliers;
This will create a table with all fields. The default value is to specify the dataType. You can update the table with relevant value or have a join in the select clause itself.
The basic syntax for creating a table from another table is as follows
CREATE TABLE NEW_TABLE_NAME AS
SELECT [ column1, column2...columnN ]
FROM EXISTING_TABLE_NAME
[ WHERE ]
Here, column1, column2... are the fields of the existing table and the same would be used to create fields of the new table.
Example
Following is an example, which would create a table SALARY using the CUSTOMERS table and having the fields customer ID and customer SALARY −
SQL> CREATE TABLE SALARY AS
SELECT ID, SALARY
FROM CUSTOMERS;
last week I did, as you want to do.
Only two steps I was followed:
Export existing table.
Open in notepad++ and change the existing table name, add my new columns and Import.
Thanks
I have a table like this:
uuid | username | first_seen | last_seen | score
Before, the table used the primary key of a "player_id" column that ascended. I removed this player_id as I no longer needed it. I want to make the 'uuid' the primary key, but there's a lot of duplicates. I want to remove all these duplicates from the table, but keep the first one (based off the row number, the first row stays).
How can I do this? I've searched up everywhere, but they all show how to do it if you have a row ID column...
I highly advocate having auto-incremented integer primary keys. So, I would encourage you to go back. These are useful for several reasons, such as:
They tell you the insert order of rows.
They are more efficient for primary keys.
Because primary keys are clustered in MySQL, they always go at the end.
But, you don't have to follow that advice. My recommendation would be to insert the data into a new table and reload into your desired table:
create temporary table tt as
select t.*
from tt
group by tt.uuid;
truncate table t;
alter table t add constraint pk_uuid primary key (uuid);
insert into t
select * from tt;
Note: I am using a (mis)feature of MySQL that allows you to group by one column while pulling columns not in the group by. I don't like this extension, but you do not specify how to choose the particular row you want. This will give values for the other columns from matching rows. There are other ways to get one row per uuid.
I have a table called events where all new information goes. This table works as a reference for all queries for news feed(s) so event items are selected from there and information corresponding to that event is retrieved from the correct tables.
Now, here's my problem. I have E_ID's in the events table which correspond to the ID of an event in a different table, be it T_ID for tracks, S_ID for status and so on... These ID's could be the same so for the time being I just used a different auto_increment value for each table so status started on 500 tracks on 0 etc. Obviously, I don't want to do that as I have no idea yet of which table is going to have the most data in it. I would assume status would quickly exceed tracks.
The information is inserted into the event table with triggers. Here's an example of one;
BEGIN
INSERT INTO events (action, E_ID, ID)
VALUES ('has some news.', NEW.S_ID, NEW.ID);
END
That ones for he status table.
Is there an addition to that trigger I can make to ensure the NEW.S_ID != an E_ID currently in events and if it does change the S_ID accordingly.
Alternatively, is there some kind of key I can use to reference events when auto incrementing the S_ID so that the S_ID is not incremented to a value of E_ID.
Those are my thoughts, I think the latter solution would be better but I doubt it is possible or it is but would require another reference table and would be too complex.
It's really uncommon to require a unique id across tables, but here's a solution that will do it.
/* Create a single table to store unique IDs */
CREATE TABLE object_ids (
id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
object_type ENUM('event', ...) NOT NULL
) ENGINE=InnoDB;
/* Independent object tables do not auto-increment, and have a FK to the object_ids table */
CREATE TABLE events (
id INT UNSIGNED NOT NULL PRIMARY KEY,
...
CONSTRAINT FOREIGN KEY (id) REFERENCES object_ids (id)
) ENGINE=InnoDB;
/* When creating a new record, first insert your object type into the object_ids table */
INSERT INTO object_ids(object_type) VALUES ('event');
/* Then, get the auto-increment id. */
SET #id = LAST_INSERT_ID();
/* And finally, create your object record. */
INSERT INTO events (id, ...) VALUES (#id, ...);
Obviously, you would duplicate the structure of the events table for your other tables.
You could also just use a Universal Unique Identifier (UUID).
A UUID is designed as a number that is globally unique in space and time. Two calls to UUID() are expected to generate two different values, even if these calls are performed on two separate computers that are not connected to each other.
Please read more about it in the manual.
There's also a shorter version.
UUID_SHORT() should do the trick.
It will generate 64-bit unsigned integers for you.
According to the doc the generator logic is:
(server_id & 255) << 56
+ (server_startup_time_in_seconds << 24)
+ incremented_variable++;
The value of UUID_SHORT() is guaranteed to be unique if the following conditions hold:
The server_id value of the current server is between 0 and 255 and is unique among your set of master and slave servers
You do not set back the system time for your server host between mysqld restarts
You invoke UUID_SHORT() on average fewer than 16 million times per second between mysqld restarts
mysql> SELECT UUID_SHORT();
-> 92395783831158784
If you curious what is your server id you can use either of these:
SELECT ##server_id
SHOW VARIABLES LIKE 'server_id';
I have table containing settings for an application with the columns: id, key, and value.
The id column is auto-incrementing but as of current, I do not use it nor does it have any foreign key constraints. I'm populating the settings and would like to restructure it so they are alphabetical as I've not been putting the settings in that way, but reordering alphabetically would help group related settings together.
For example, if I have the following settings:
ID KEY VALUE
======================================
1 App.Name MyApplication
2 Text.Title Title of My App
3 App.Version 0.1
I would want all the App.* settings to be grouped together sequential without having to do an ORDER BY everytime. Anyway, thats the explanation. I have tried the following and it didn't seem to change the order:
CREATE TABLE mydb.Settings2 LIKE mydb.Settings;
INSERT INTO mydb.Settings2 SELECT `key`,`value` FROM mydb.Settings ORDER BY `key` ASC;
DROP TABLE mydb.Settings;
RENAME TABLE mydb.Settings2 TO mydb.Settings;
That will make a duplicate of the table as suggested, but won't restructure the data. What am I missing here?
The easy way to reorder a table is with ALTER TABLE table ORDER BY column ASC. The query you tried looks like it should have worked, but I know the ALTER TABLE query works; I use it fairly often.
Note: Reordering the data in a table only works and makes sense in MyISAM tables. InnoDB always stores data in PRIMARY KEY order, so it can't be rearranged.
Decided to make that an answer.
As I said in a comment to the initial answer, for you to achieve a long term effect you need to recreate the settings table with the key column as the PRIMARY KEY. Because as G-Nugget correctly said 'InnoDB always stores data in PRIMARY KEY order'.
You can do that like this
CREATE TABLE settings2
(`id` int NULL, `key` varchar(64), `value` varchar(64), PRIMARY KEY(`key`));
INSERT INTO settings2
SELECT id, `key`, `value`
FROM settings;
DROP TABLE settings;
RENAME TABLE settings2 TO settings;
That way you get your order intact after inserting new records.
And if you don't need the initial id column in settings table it's a good time to ditch it.
Here is working sqlfiddle
Disclaimer: Personally I would use ORDER BY anyway
I've read some posts about this but none cover this issue.
I guess its not possible, but I'll ask anyway.
I have a table with more than 50.000 registers. It's an old table where various insert/delete operations have taken place.
That said, there are various 'holes' some of about 300 registers. I.e.: ..., 1340, 1341, 1660, 1661, 1662,...
The question is. Is there a simple/easy way to make new inserts fill these 'holes'?
I agree with #Aaron Digulla and #Shane N. The gaps are meaningless. If they DO mean something, that is a flawed database design. Period.
That being said, if you absolutely NEED to fill these holes, AND you are running at least MySQL 3.23, you can utilize a TEMPORARY TABLE to create a new set of IDs. The idea here being that you are going to select all of your current IDs, in order, into a temporary table as such:
CREATE TEMPORARY TABLE NewIDs
(
NewID INT UNSIGNED AUTO INCREMENT,
OldID INT UNSIGNED
)
INSERT INTO NewIDs (OldId)
SELECT
Id
FROM
OldTable
ORDER BY
Id ASC
This will give you a table mapping your old Id to a brand new Id that is going to be sequential in nature, due to the AUTO INCREMENT property of the NewId column.
Once this is done, you need to update any other reference to the Id in "OldTable" and any foreign key it utilizes. To do this, you will probably need to DROP any foreign key constraints you have, update any reference in tables from the OldId to the NewId, and then re-institute your foreign key constraints.
However, I would argue that you should not do ANY of this, and just understand that your Id field exists for the sole purpose of referencing a record, and should NOT have any specific relevance.
UPDATE: Adding an example of updating the Ids
For example:
Let's say you have the following 2 table schemas:
CREATE TABLE Parent
(
ParentId INT UNSIGNED AUTO INCREMENT,
Value INT UNSIGNED,
PRIMARY KEY (ParentId)
)
CREATE TABLE Child
(
ChildId INT UNSIGNED AUTO INCREMENT,
ParentId INT UNSIGNED,
PRIMARY KEY(ChildId),
FOREIGN KEY(ParentId) REFERENCES Parent(ParentId)
)
Now, the gaps are appearing in your Parent table.
In order to update your values in Parent and Child, you first create a temporary table with the mappings:
CREATE TEMPORARY TABLE NewIDs
(
Id INT UNSIGNED AUTO INCREMENT,
ParentID INT UNSIGNED
)
INSERT INTO NewIDs (ParentId)
SELECT
ParentId
FROM
Parent
ORDER BY
ParentId ASC
Next, we need to tell MySQL to ignore the foreign key constraint so we can correctly UPDATE our values. We will use this syntax:
SET foreign_key_checks = 0;
This causes MySQL to ignore foreign key checks when updating the values, but it will still enforce the correct value type is used (see MySQL reference for details).
Next, we need to update our Parent and Child tables with the new values. We will use the following UPDATE statement for this:
UPDATE
Parent,
Child,
NewIds
SET
Parent.ParentId = NewIds.Id,
Child.ParentId = NewIds.Id
WHERE
Parent.ParentId = NewIds.ParentId AND
Child.ParentId = NewIds.ParentId
We now have updated all of our ParentId values correctly to the new, ordered Ids from our temporary table. Once this is complete, we can re-institute our foreign key checks to maintain referential integrity:
SET foreign_key_checks = 1;
Finally, we will drop our temporary table to clean up resources:
DROP TABLE NewIds
And that is that.
What is the reason you need this functionality? Your db should be fine with the gaps, and if you're approaching the max size of your key, just make it unsigned or change the field type.
You generally don't need to care about gaps. If you're getting to the end of the datatype for the ID it should be relatively easy to ALTER the table to upgrade to the next biggest int type.
If you absolutely must start filling gaps, here's a query to return the lowest available ID (hopefully not too slowly):
SELECT MIN(table0.id)+1 AS newid
FROM table AS table0
LEFT JOIN table AS table1 ON table1.id=table0.id+1
WHERE table1.id IS NULL
(remember to use a transaction and/or catch duplicate key inserts if you need concurrent inserts to work.)
INSERT INTO prueba(id)
VALUES (
(SELECT IFNULL( MAX( id ) , 0 )+1 FROM prueba target))
IFNULL for skip null on zero rows count
add target for skip error mysql "error clause FROM)
There is a simple way but it doesn't perform well: Just try to insert with an id and when that fails, try the next one.
Alternatively, select an ID and when you don't get a result, use it.
If you're looking for a way to tell the DB to automatically fill the gaps, then that's not possible. Moreover, it should never be necessary. If you feel you need it, then you're abusing an internal technical key for something but the single purpose it has: To allow you to join tables.
[EDIT] If this is not a primary key, then you can use this update statement:
update (
select *
from table
order by reg_id -- this makes sure that the order stays the same
)
set reg_id = x.nextval
where x is a new sequence which you must create. This will renumber all existing elements preserving the order. This will fail if you have foreign key constraints. And it will corrupt your database if you reference these IDs anywhere without foreign key constraints.
Note that during the next insert, the database will create a huge gap unless you reset the identity column.
As others have said, it doesn't matter, and if it does then something is wrong in your database design. But personally I just like them to be in order anyway!
Here is some SQL that will recreate your IDs in the same order, but without the gaps.
It is done first in a temp_id field (which you will need to create), so you can see that it is all good before overwriting your old IDs. Replace Tbl and id as appropriate.
SELECT #i:=0;
UPDATE Tbl
JOIN
(
SELECT id
FROM Tbl
ORDER BY id
) t2
ON Tbl.id = t2.id
SET temp_id = #i:=#i+1;
You will now have a temp_id field with all of your shiny new IDs. You can make them live by simply:
UPDATE Tbl SET id = temp_id;
And then dropping your temp_id column.
I must admit I'm not quite sure why it works, since I would have expected the engine to complain about duplicate IDs, but it didn't when I ran it.
You might wanna clean up gaps in a priority column.
The way below will give an auto increment field for the priority.
The extra left join on the same tabel will make sure it is added in the same order as (in this case) the priority
SET #a:=0;
REPLACE INTO footable
(id,priority)
(
SELECT tbl2.id, #a
FROM footable as tbl
LEFT JOIN footable as tbl2 ON tbl2.id = tbl.id
WHERE (select #a:=#a+1)
ORDER BY tbl.priority
)