I have a table with id column as a number which have meanings. Different types of accounts start from different ranges. E.g Organisation 10000 <-> 100000, users 1000000 <-> 1kk. How can i properly increment ids on insert (with possible concurrency problem)?
If you were doing this in Oracle's table server, you would use different SEQUENCE objects for each type of account.
The MariaDB fork of MySQL has a similar kind of SEQUENCE object, as does PostgreSQL. So if you were using MariaDB you would do something like this.
CREATE SEQUENCE IF NOT EXISTS org_account_id MINVALUE=10000 MAXVALUE=999999;
CREATE SEQUENCE IF NOT EXISTS user_account_id MINVALUE=1000000;
Then to use a sequence in place of autoincrement you'll do something like this.
INSERT INTO tbl (id, col1, col2)
VALUES (NEXTVAL(user_account_id), something, something);
In MySQL you can emulate sequence objects with dummy tables containing autoincrement ids. It's a kludge. Create the following table (one for each sequence).
CREATE TABLE user_account_id (
sequence_id BIGINT NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`sequence_id`)
);
ALTER TABLE user_account_id AUTO_INCREMENT=1000000;
Then issue these queries one after the other to insert a row with a unique user id.
INSERT INTO user_account_id () VALUES ();
DELETE FROM sequence WHERE sequence_id < LAST_INSERT_ID();
SET #id:=LAST_INSERT_ID();
INSERT INTO tbl (id, col1, col2)
VALUES (#id, something, something);
After your insert into the dummy table, LAST_INSERT_ID() returns a unique id. The DELETE query merely keeps this dummy table from taking up too much space.
I recommend that you use a normal sequence-based bigint column. Then, on SELECT, add the base for the appropriate account type to the column.
PreparedStatement ps = con.prepareStatement("insert into emp(emp_code,emp_name,join_date,designation,birth_date,gender,mobile) values((select max(emp_code)+1 from emp),?,?,?,?,?,?)")
This query will definitely help..
Related
I created a table in MySql
CREATE TABLE newuser(id VARCHAR(10) PRIMARY KEY,sname VARCHAR(20));
When I INSERT record it works fine
INSERT INTO newuser VALUE('abc123','monika');
But sometimes I don't want to supply id in the INSERT query and sometimes I want to supply. In case I don't supply id MySql automatically generate one.
What can I do to get both below query works?
INSERT INTO newuser VALUE('abc123','monika');
INSERT INTO newuser VALUE('nikita');
'I don't understood ANYTHING' - very new then.
Firstly second insert statement is invalid please review https://dev.mysql.com/doc/refman/8.0/en/insert.html -
'If you do not specify a list of column names for INSERT ... VALUES or INSERT ... SELECT, values for every column in the table must be provided by the VALUES list, SELECT statement, or TABLE statement.'
Secondly uuid is a function in which 'A UUID is designed as a number that is globally unique in space and time.' https://dev.mysql.com/doc/refman/8.0/en/insert.html
You can easily select uuid() to see what it produces.
You will need to increase the id size
If you wish to use it in an insert
insert into users values (uuid(),<sname>);
I need two columns in table that would have same value on insert. Is there any way to do it from database side?
So you want to let one column use the auto_increment feature, but make another column in the same table also have the same value?
I can't think of a reason you would need this feature. Perhaps you could explain what you're trying to accomplish, and I can suggest a different solution?
A trigger won't work for this. It's a chicken-and-egg problem:
You can't change any column's value in an AFTER trigger.
But the auto-increment value isn't set yet when a BEFORE trigger executes.
It also won't work to use a MySQL 5.7 GENERATED column:
CREATE TABLE MyTable (
id INT AUTO_INCREMENT PRIMARY KEY,
why_would_you_want_this INT GENERATED ALWAYS AS (id)
);
ERROR 3109 (HY000): Generated column 'why_would_you_want_this'
cannot refer to auto-increment column.
You can't do it in a single SQL statement. You have to INSERT the row, and then immediately do an UPDATE to set your second column to the same value.
CREATE TABLE MyTable (
id INT AUTO_INCREMENT PRIMARY KEY,
why_would_you_want_this INT
);
INSERT INTO MyTable () VALUES ();
UPDATE MyTable SET why_would_you_want_this = LAST_INSERT_ID()
WHERE id = LAST_INSERT_ID();
You could alternatively generate the ID value using some other mechanism besides AUTO_INCREMENT (for example a Memcached incrementing key). Then you could insert the new value in both columns:
INSERT INTO MyTable (id, why_would_you_want_this) VALUES ($gen_id, $gen_id);
Define a before or after insert trigger and assign the value of the 2nd field in the trigger.
If the 1st field is an auto increment column, then you need to use an after insert trigger. If your application assigns value to the 1st field, then you can use a before insert trigger.
However, I would no necessarily duplicate the value on insert. You can leave the 2nd field as null on insert, which would mean that its value is the same as the 1st field's. The only drawback of this approach is that it may be more difficult to create joins on the 2nd field.
You can do this in one query by using the primary key (assumed to be id) and setting your column (assumed to be columnName):
"INSERT INTO tableName SET `columnName` = (SELECT MAX(x.id) FROM tableName x)+1"
This will not work if you have deleted the most recent primary key row however. To get past this, you can insert into the id as well:
"INSERT INTO tableName SET `columnName` = (SELECT MAX(x.id) FROM tableName x)+1, `id`= (SELECT MAX(x.id) FROM tableName x)+1"
However, this solution has the downside (or upside depending on the case) of reusing primary key values that have already been deleted.
suggested way:
To use the actual auto_increment value, you can do this:
"INSERT INTO tableName SET `columnName` = (SELECT `AUTO_INCREMENT` FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'db_name' AND TABLE_NAME = 'table_name')"
Sources that helped me solve this: Prashant Pimpale's answer
I have a table with 3 fields: Id(PK,AI), Name(varchar(36)), LName(varchar(36)).
I have to insert name and last name, Id inserts automatically because of it's constraints,
Is There a way to Jump id auto increment value when it reaches 6?
for instance do this 7 times:
Insert Into table(Name, LName) Values ('name1', 'lname1') "And jump id to 7 if it is going to be 6"
It may sound stupid to do this but I have the doubt.
Also Jump and do not record id 6.
record only, 1-5, 7,8,9 and so on
What I want to achieve starts from a Union:
Select * From TableNames
Union All
Select * From TableNames_general
In the TableNames_general I assign it's first value so that when the user sees the table for the first time it will be displayed the record I inserted.
The problem comes when the user inserts a new record, if the Id of the inserted record is the same as the one I have inserted it will be duplicated, that is why I want to achieve when the users inserts one record and if the last insert id already exists just jump that record. this is because I must have different ids due to its relationship among child tables.
Identity column generate values for you, And its best left this way, You have the ability to insert specific values in Identity column but its best left alone and let it generate values for you.
Imagine you have inserted a value explicitly in an identity column and then later on Identity column generates the same value for you, you will end up with duplicates.
If you want to have your input in that column then why bother with identity column anyway ??
Well this is not the best practice but you can jump to a specific number by doing as follows:
MS SQL SERVER 2005 and Later
-- Create test table
CREATE TABLE ID_TEST(ID INT IDENTITY(1,1), VALUE INT)
GO
-- Insert values
INSERT INTO ID_TEST (VALUE) VALUES
(1),(2),(3)
GO
-- Set idnentity insert on to insert values explicitly in identity column
SET IDENTITY_INSERT ID_TEST ON;
INSERT INTO ID_TEST (ID, VALUE) VALUES
(6, 6),(8,8),(9,9)
GO
-- Set identity insert off
SET IDENTITY_INSERT ID_TEST OFF;
GO
-- 1st reseed the value of identity column to any smallest value in your table
-- below I reseeded it to 0
DBCC CHECKIDENT ('ID_TEST', RESEED, 0);
-- execute the same commad without any seed value it will reset it to the
-- next highest idnetity value
DBCC CHECKIDENT ('ID_TEST', RESEED);
GO
-- final insert
INSERT INTO ID_TEST (VALUE) VALUES
(10)
GO
-- now select data from table and see the gap
SELECT * FROM ID_TEST
If you query the database to get the last inserted ID, then you can check if you need to increment it, by using a parameter in the query to set the correct ID.
If you use MSSQL, you can do the following:
Before you insert check for the current ID, if it's 5, then do the following:
Set IDENTITY_INSERT to ON
Insert your data with ID = 7
Set IDENTITY_INSERT to OFF
Also you might get away with the following scenario:
check for current ID
if it's 5, run DBCC CHECKIDENT (Table, reseed, 6), it will reseed the table and in this case your next identity will be 7
If you're checking for current identity just after INSERT, you can use SELECT ##IDENTITY or SELECT SCOPE_IDENTITY() for better results (as rcdmk pointed out in comments)
Otherwise you can just use select: SELECT MAX(Id) FROM Table
There's no direct way to influence the AUTO_INCREMENT to "skip" a particular value, or values on a particular condition.
I think you'd have to handle this in an AFTER INSERT trigger. An AFTER INSERT trigger can't update the values of the row that was just inserted, and I don't think it can make any modifications to the table affected by the statement that fired the trigger.
A BEFORE INSERT trigger won't work either, because the value assigned to an AUTO_INCREMENT column is not available in a BEFORE INSERT trigger.
I don't believe there's a way to get SQL Server IDENTITY to "skip" a particular value either.
UPDATE
If you need "unique" id values between two tables, there's a rather ugly workaround with MySQL: roll your own auto_increment behavior using triggers and a separate table. Rather than defining your tables with AUTO_INCREMENT attribute, use a BEFORE INSERT trigger to obtain a value.
If an id value is supplied, and it's larger than the current maximum value from the auto_increment column in the dummy auto_increment_seq table, we'd need to either update that row, or insert a new one.
As a rough outline:
CREATE TABLE auto_increment_seq
(id INT NOT NULL PRIMARY KEY AUTO_INCREMENT) ENGINE=MyISAM;
DELIMITER $$
CREATE TRIGGER TableNames_bi
BEFORE INSERT ON TableNames
FOR EACH ROW
BEGIN
DECLARE li_new_id INT UNSIGNED;
IF ( NEW.id = 0 OR NEW.id IS NULL ) THEN
INSERT INTO auto_increment_seq (id) VALUES (NULL);
SELECT LAST_INSERT_ID() INTO li_new_id;
SET NEW.id = li_new_id;
ELSE
SELECT MAX(id) INTO li_max_seq FROM auto_increment_seq;
IF ( NEW.id > li_max_seq ) THEN
INSERT INTO auto_increment_seq (id) VALUES (NEW.id);
END IF;
END IF;
END$$
CREATE TRIGGER TableNames_ai
AFTER INSERT ON TableNames
FOR EACH ROW BEGIN
DECLARE li_max_seq INT UNSIGNED;
SELECT MAX(id) INTO li_max_seq FROM auto_increment_seq;
IF ( NEW.id > li_max_seq ) THEN
INSERT INTO auto_increment_seq (id) VALUES (NEW.id);
END IF;
END;
DELIMITER ;
The id column in the table could be defined something like this:
TableNames
( id INT UNSIGNED NOT NULL DEFAULT 0 PRIMARY KEY
COMMENT 'populated from auto_increment_seq.id'
, ...
You could create an identical trigger for the other table as well, so the two tables are effectively sharing the same auto_increment sequence. (With less efficiency and concurrency than an Oracle SEQUENCE object would provide.)
IMPORTANT NOTES
This doesn't really insure that the id values between the tables are actually kept unique. That would really require a query of the other table to see if the id value exists or not; and if running with InnoDB engine, in the context of some transaction isolation levels, we might be querying a stale (as in, consistent from the point in time at the start of the transaction) version of the other table.
And absent some additional (concurrency killing) locking, the approach outline above is subject to a small window of opportunity for a "race" condition with concurrent inserts... the SELECT MAX() from the dummy seq table, followed by the INSERT, allows a small window for another transaction to also run a SELECT MAX(), and return the same value. The best we can hope for (I think) is for an error to be thrown due to a duplicate key exception.
This approach requires the dummy "seq" table to use the MyISAM engine, so we can get an Oracle-like AUTONOMOUS TRANSACTION behavior; if inserts to the real tables are performed in the context of a REPEATABLE READ or SERIALIZABLE transaction isolation level, reads of the MAX(id) from the seq table would be consistent from the snapshot at the beginning of the transaction, we wouldn't get the newly inserted (or updated) values.
We'd also really need to consider the edge case of an UPDATE of row changing the id value; to handle that case, we'd need BEFORE/AFTER UPDATE triggers as well.
Is there a way to create a table in MySql that it has an automatic ID field, but the ID is not sequential. For example, a random or pseudo random ID.
I have found solutions that suggest generating an ID and try to insert it until an unused ID is found (generating an sequential five digit alphanumerical ID).
but nothing that can be done directly in the table definition, or a simpler trick.
MySQL has a native function UUID() which will generate a globally unique identifier:
mysql> SELECT UUID();
-> '6ccd780c-baba-1026-9564-0040f4311e29'
You can store its output in a CHAR(36) column.
INSERT INTO table (`uuid`, `col1`, `col2`) VALUES (UUID(), 'someval', 'someval');
According to the documentation though,
Although UUID() values are intended to be unique, they are not necessarily unguessable or unpredictable. If unpredictability is required, UUID values should be generated some other way.
Addendum Another option is UUID_SHORT() for a 64-bit unsigned INT rather than a character field.
mysql> SELECT UUID_SHORT();
-> 92395783831158784
Since you asked for a trick, you could use a common auto_incremented id and "fake" it by multiplying with a big prime (and then modulo 2^32):
CREATE TABLE AutoIncPrime
(id int unsigned auto_increment primary key
) ;
Insert values, from 1 to 10:
INSERT INTO AutoIncPrime
VALUES (),(),(),(),(),(),(),(),(),() ;
SELECT * FROM AutoIncPrime ;
Output:
id
---
1
2
3
4
5
6
7
8
9
10
Fake the id, with a View:
CREATE VIEW AutoIncPrime_v AS
SELECT
((id*1798672429 ) & 0xFFFFFFFF)
AS FakeUUID
FROM AutoIncPrime ;
Lets see our "UUIDs":
SELECT * FROM AutoIncPrime_v ;
Output:
FakeUUID
----------
1798672429
3597344858
1101049991
2899722420
403427553
2202099982
4000772411
1504477544
3303149973
806855106
You could even make it look more random with (more complicated bit mixing):
CREATE VIEW AutoIncPrime_v2 AS
SELECT
( (((id*1798672429 ) & 0x55555555) << 1)
| (((id*1798672429 ) & 0xAAAAAAAA) >> 1)
)
AS FakeUUID
FROM AutoIncPrime ;
SELECT * FROM AutoIncPrime_v2 ;
FakeUUID
----------
2537185310
3918991525
2186309707
1558806648
604496082
1132630541
3719950903
2791064212
3369149034
808145601
The trick is that you still have a sequential id in the table - which you can use to join to other tables. You just don't show it to the users - but only show the fake one.
If the table is to get big and the calculations slow, you can add another column in the table and store the FakeUUID value there with an INSERT trigger.
Would a composite key work? A regular standard auto_increment field. You insert your new record, retrieve its new ID, then hash that ID with a salt, and update the record with that hash value.
If you do this all within a transaction, the in-progress version of the record without the hash will never be visible until the hash is generated. And assuming you've done proper salting, the resulting hash value will be for all intents and purposes 'random'.
Note that you can't do this in a single step, as the value of last_insert_id() in mysql is not updated with the new id until the record is actually written. The value retrieved during the actual insert parseing stage would be whatever id was inserted BEFORE this one.
The only automatically generated default in the table definition allowed would be autoincrement (MySQL Guide).
You should be able to write a trigger to automate this process though, maybe through the UUID function as Michael suggested.
I have two mysql tables, one needs to start its auto-increment column id with the last value of the last inserted row in the other table (plus 1).
According to mysql manual you can restart the value of an auto increment column like this:
mysql> ALTER TABLE tbl AUTO_INCREMENT = 100;
However, this is not possible:
mysql> ALTER TABLE tb2 AUTO_INCREMENT = (SELECT MAX(id) FROM tbl1);
I need to perform something like this because I'm filling the tables using a script. Is there another way to achieve it?
I think you are trying to use the auto-increment column for something it is not well suited to. If you care about the exact values that get inserted then it shouldn't be auto-increment.
IT IS USING THIS SCRIPT
ALTER TABLE `people` AUTO_INCREMENT =1
where people is my table, or you can do this through GUI (operation tab of phpmyadmin with current table selected)
What about create a dummy record and increment?
-- insert dummy forcing id
INSERT INTO 'tb2' (ID, NAME, ...)
VALUES (SELECT MAX(id) FROM tb1, "dummy", ...);
-- automagically increment to last id + 1
ALTER TABLE `tb2' AUTO_INCREMENT = 1; -- only myISAM
-- delete dummy
DELETE FROM 'tb2' WHERE NAME="dummy";