I'm trying to put the number of id in the neighbor column. Something like this:
+----+-------------------+
| id | identical_with_id |
+----+-------------------+
id is AUTO INCREMENT and all need is getting id's number when inserting. I can do that like this:
INSERT INTO `table_name`
VALUES( NULL,
(SELECT `AUTO_INCREMENT` FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'database_name' AND
TABLE_NAME = 'table_name')
);
But I don't know it will work all the time. Maybe between executing that sub-query and inserting that row, a new row (another row) get insert. In this case the number of id will not be the same as neighbor column. Hum? is that possible?
Note: Please don't tell me: "what do you need this for?"
Usually everyone sometimes need to do such things. And it's best to not ask for reasons :)
I think you are doing it in correct way but you need to check which MySql engine you are using and make sure that inserts are executed sequentially.
Usually insert statement will lock the table and unlock when it's finished. That means your query for retrieving auto increment is pretty much safe.
For MySql engine and related settings this post can help you:
Does a MySQL multi-row insert grab sequential autoincrement IDs?
For InnoDb:
http://dev.mysql.com/doc/refman/5.1/en/innodb-auto-increment-handling.html
You could use LAST_INSERT_ID() right after your query.
INSERT INTO `table_name` VALUES( NULL, NULL);
SELECT LAST_INSERT_ID() INTO #last_id;
UPDATE `table_name` SET duplicate_id_column = #last_id WHERE id = #last_id;
Related
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..
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 primary key (its name is "id") defined as auto_increment. I use NULL in INSERT statements to "fill" the id value. It works, of course. However now I need to "move" an existing record to a new primary key value (the next available, the value is not so much important, but it must be a new one, and the last one if ordered by id). How can I do it in an "elegant" way? Since the "use NULL at INSERT" does not work too much with UPDATE:
update idtest set id=NULL where id=1;
This simply makes the id of the record zero. I would expect to do the same thing as with INSERT, but it seems my idea was incorrect.
Of course I can use "INSERT ... SELECT" statement, then a DELETE on the old one, or I can use something like MAX(id) + 1 to UPDATE the id of the old record in one step, etc, but I am curious if there is a finer solution.
Also, the MAX(id) solution doesn't seem to work either by the way:
mysql> update idtest set id=max(id)+1 where id=3;
ERROR 1111 (HY000): Invalid use of group function
mysql> update idtest set id=(select max(id)+1 from idtest) where id=3;
ERROR 1093 (HY000): You can't specify target table 'idtest' for update in FROM clause
This is the way I believe:
UPDATE users SET id = (SELECT `AUTO_INCREMENT`
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'test'
AND TABLE_NAME = 'users') WHERE id = 2;
select * from users;
I used by own tables substitute yours.
test is database name, users is table name and id is AUTO_INCREMENT in my case.
EDIT: My Query above works perfect but its side effects are somewhat 'dangerous', upon next insert as AUTO_INCREMENT value will collide with this recently updated record so just next single insert will fail. To avoid that case I've modified above query to a transaction:
START transaction;
UPDATE users SET id = (SELECT `AUTO_INCREMENT`
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'test'
AND TABLE_NAME = 'users') WHERE id = 2;
#renew auto increment to avoid duplicate warning on next insert
INSERT IGNORE INTO users(username) values ('');
COMMIT
Hope this will help someone if not OP.
The way you are trying to update same table is wrong but you can use join on same table
update idtest t
join (select id +1 as id
from idtest order by id desc
limit 1) t1
set t.id=t1.id
where t.id=3;
or
update idtest t
join (select max(id) +1 as id
from idtest ) t1
set t.id=t1.id
where t.id=3;
You can use the REPLACE INTO clause to do the trick.
From the manual:
REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted. See Section 13.2.5, "INSERT Syntax".
EDIT
My mistake (in the comments) that you have to have two unique constraint to achieve this:
When you use the auto_increment value to REPLACE the record, the record will be replaced with the give ID and will not change (however the AI value will increment).
You have to exclude the AI column from the query. You can do that if you have one more UQ constraint.
Check this SQLFiddle demo: http://sqlfiddle.com/#!2/1a702e
The first query will replace all the records (but the id's value will not change).
The second one will replace it too, and the new AI value will be used. (Please note, that the second query does not contain the id column, and there is a UQ constraint on the some column).
You can notice, that the second query uses higher AI values than it is excepted: this is because the first replace incremented the AI value.
If you do not have two unique keys (one for the AI and one for another columns), the REPLACE statement will work as a normal INSERT statement!
(Ofcourse you can change one of the UNIQUE KEYs with a PRIMARY KEY)
When inserting a row into a table with an auto increment primary key column, is there a way to get the value that is going to be assigned to that row?
To be clear, I want to use this value as a part of a string for a different column on the same row.
Doing MAX(id) + 1 doesn't seem robust enough.
And doing the insert and then an update with LAST_INSERT_ID() is bad because that's 2 separate db calls.
Thanks
EDIT:
What does everyone think of this:
INSERT INTO `mydatabase`.`mytable` (`name`, `description`)
VALUES
(
CONCAT(
'name-',
CAST(
(SELECT
`auto_increment` + 1
FROM
`information_schema`.`TABLES`
WHERE `TABLE_SCHEMA` = 'mydatabase'
AND `TABLE_NAME` = 'mytable') AS CHAR
)
),
'description of this thing'
) ;
This way, you should end up with a row with id of 5 for example, and a name of "name-5". This is kind of a messy way to go about it, but it should work, no?
Thoughts?
You should look in to the SQL command "SHOW TABLE STATUS"
Try it, and google further to find out how to pull the "auto_increment" value out of it.
You can't do with auto_increment field. Instead you can manually generate UID (unique primary key) and use it for this purpose.
Ain't that bad. If you're not generating the key externally, then no. You could put a trigger on the table and make that a non auto increment and then generate the key yourself otherwise.
How can I edit the latest row in the database. I only know it's the last one. I don't know its id.
I don't know which language you are working with, in PHP's mySQL functions you can use
mysql_insert_id()
there are similar function in every other mySQL client library I know of.
Also, there is a native mySQL function!
LAST_INSERT_ID() (with no argument)
returns the first automatically
generated value that was set for an
AUTO_INCREMENT column by the most
recently executed INSERT statement to
affect such a column. For example,
after inserting a row that generates
an AUTO_INCREMENT value, you can get
the value like this:
mysql> SELECT LAST_INSERT_ID();
-> 195
Of course, a primary key with AUTO_INCREMENT is required for these functions to work.
For a table with an auto_increment id field:
UPDATE tbl SET col1 = 'val1' WHERE id = MAX(id);
If it's a row that has been inserted in your script (the same script from which you want to update it) and there is an auto_increment column on your table, you can get that auto_increment value, using functions such as those, for PHP :
mysql_insert_id
mysqli_insert_id
PDO::lastInsertId
There should be an equivalent for probably any language you can possibly be using for your application.
If your are trying to do an update from another script than the one in which you did the insert, and still have an auto_increment column, the best way will probably be to update the row that has the biggest value for that column :
update your_table
set your_column = ...
where id = max(id)
Or, in two steps (not sure it'll work in one) :
select max(id) as id from your_table
update your_table set your_column = ... where id = [what you got with thr first query]
You can also use UPDATE table SET ... WHERE id=LAST_INSERT_ID() (supposing the last insert was on the table you want to query).
I would not use TWO steps to find the last insert ID simply because a new record could be added in the mean time.
Depending on your version, you should be able to call $handle->last_id(); or $handle->{mysql_insertid};
Chris