Right now, I have my database setup so that I insert a new row. But if the row I'm trying to insert is a duplicate (based off of my primary key id), then I increment the count field by 1.
Right now I want to know when I was able to create a new row instead of having it increment count. How would I do this in an efficient/proper manner?
The current method I'm thinking of doing this, is by querying the id first and checking if it exists. But I feel like there's a faster/better way. I've also read about triggers but I've heard that they're bad/risky to use.
Use INSERT ... ON DUPLICATE KEY UPDATE...
Then query for affected_rows (as #Tarek Fadel suggested). MySQL will return 1 if the row was inserted, or 2 if existing row were updated.
Use your database AUTO INCREMENT option for your primary ID field. Only propper solution.
Here you have mysql reference, but that exist in just every database engine:
http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html
How about an auto_increment on the id column?
Otherwise you might use SELECT MAX(id) FROM TABLE to retreive the highest id and add one to it, but that isn't thread-safe since another user might execute the same insert at the same time. Auto_increment fixes that for you.
PHP's mysql_affected_rows()
Related
I have some tables in my phpmyadmin with one column that is auto incremented.
The problem is that when I delete some rows from the table (For example the element Car, with index auto incremented 1) and I create another row into the table, the new row have the index 2, but in the table there is only one row.
I want that this second element created to have the index equal to the position of the row, for example, if I have 3 rows that the third element will have the index equals to 3.
I was looking for a method that let me to use my phpMyAdmin like this but I couldn't find anything.
Is it possible? If it is true, what should I have to do? Do I have to create the table again?
This is generally a bad idea. Auto increment is used for creating unique ID of the row. Imagine you have a record "1 - John". Then you delete it and add another "1 - Jack". From the point of common database logic, it will seem that John was renamed to Jack (it has the same ID = it is the same entity) rather than it is another record. You should let DB assign new ID to each new record, even with leaving gaps after deleted records.
If you really want to do so, you can modify auto increment value using this query:
ALTER TABLE users AUTO_INCREMENT=123
but it is still not the way auto increment is designed for.
It is possible, but you shouldn't do that on production.
The SQL query is:
ALTER TABLE tablename AUTO_INCREMENT = 1
The most important part of this is to prevent overriding. For example you have an user and this user has id of 81 and if you delete this user and the database doesn't remember that this id 81 has ever been taken by an user (and for example, you have some relations - like friend lists) the user that is going to have the same ID will probably have the same data.
So basically, you don't want to reset auto increment values.
Execute this SQL sentence:
ALTER TABLE tablename AUTO_INCREMENT = 1
I struggled with this a bit too, then found in the "Operations" tab, there is a setting under "Auto Increment" where you can set the number it will start from, so you can roll it back if you want to do that.
It is possible. It is not a feature of phpmyadmin, but of mysql. Execute this
ALTER TABLE tablename AUTO_INCREMENT = 1
More info on this on stackoverflow
And in the mysql reference
I want to write a function that returns the value of a column (in this case, an auto-incrementing primary key) for a row that it inserts.
Essentially, I want to insert some new data, have a new primary key generated, then get that key. I could simply look for the highest primary key in the table, but it is possible that someone else could be running the function as well, and I could return the wrong key, right?
What's the simplest way to negotiate this problem?
As pointed in the comments, from MySQL documentation:
mysql> SELECT LAST_INSERT_ID();
-> 195
This LAST_INSERT_ID() function is not subject to a race condition like SELECT MAX(id) might be, because it's maintained within MySQL specific to your connection. It returns the ID generated for your last insert, not anybody's last insert.
Just looking for some tips and pointers for a small project I am doing. I have some ideas but I am not sure if they are the best practice. I am using mysql and php.
I have a table called nomsing in the database.
It has a primary key called row id which is an integer.
Then I have about 8 other tables referencing this table.
That are called nomplu, accsing,accplu, datsing, datplu for instance.
Each has a column that references the primary key of nomsing.
Withing my php code I have all the information to insert into the tables except one thing , the row id primary key of the nomsing table. So that php generates a series of inserts like the following.
INSERT INTO nomsing(word,postress,gender) VALUES (''велосипед","8","mask").
INSERT INTO nomplu(word,postress,NOMSING?REFERENCE) VALUES (''велосипеды","2",#the reference to the id of the first insert#).
There are more inserts but this one gets the point across. The second insert should reference the auto generated id for the first insert. I was this to work as a transaction so all inserts should complete or none.
One idea I have is to not auto generate the id and generate it myself in php. That way would know the id given before the transaction but then I would have to check if the id was already in the db.
Another idea I have is to do the first insert and then query for the row id of that insert in php and then make the second insert. I mean both should work but they don't seem like an optimal solution. I am not too familiar with the database transactional features but what would be the best approach to do in this case. I don't like the idea of inserting then querying for the id and then running the rest of the queries. Just seems very inefficient or perhaps I am wrong.
Just insert a row in the master table. Then you can fetch the insert id ( lastInserId when on PDO) and use that to populate your other queries.
You could use the php version as given by JvdBerg , or Mysql's LAST_INSERT_ID. I usually use the former option.
See a similar SO question here.
You could add a new column to the nomsing table, called 'insert_order' (or similar) with a default value of 0, then instead of generating one SQL statement per insert create a bulk insert statement e.g.
INSERT INTO nomsing(word,postress,gender, insert_order)
VALUES (''велосипед","8","mask",1), (''abcd'',"9","hat",2).....
you generate the insert_order number with a counter in your loop starting at one. Then you can perform one SELECT on the table to get the ids e.g.
SELECT row_id
FROM nomsing
WHERE insert_order > 0;
now you have all the IDs you can now do a bulk insert for your following queries. At the end of your script just do an update to reset the insert_order column back to 0
UPDATE nomsing SET insert_order = 0 WHERE insert_order > 0;
It may seem messy to add an extra column to do this but it will add a significant speed increase over performing one query at a time.
Let's say I have a MySQL table and a table has a row with id and it has auto_incremented. Let's say via MySQL query and PHP, I add a row. The first row has id of 1. Then I manually add a second row (via phpmyadmin) with the id of 2. If I do a third MySQL insert via PHP... what would the id be for the third row... 2 or 3?
Question is... does auto_increment take into account manual inputs?
does auto_increment take into account manual inputs?
Yes it does. But I hope you do not really type in the ID manually, right? :-) Just leave this field alone when inserting (manually or programatically), MySQL will take care of it for you.
MySQL does accept manual inputs, and it WILL try to set the value you offer. If the value does not exist, it gets inserted, else you get a duplicate key error.
Put a value when you want to decide a value yourself (for example,
you deleted a line, and now want the exact same line in the table).
Put NULL or leave the column out of the insert to let the database
use the auto-increment.
Just a hint: when your application is choosing the values to put for an autoincrement value, you are probably doing something wrong.
My db table looks like this pic. http://prntscr.com/22z1n
Recently I've created delete.php page. it works properly but when i deleted 21th user next registered user gets 24th id instead of 21.
Is it possible to put newly registered users info to first empty row? (In this situation 21th row)
In my registration form, newly registering user can write names of existing users, and be friends with them after registration. For this friendship i have another table that associates id of newly registered user and existing user.
For this purpose i'm using mysql_insert_id during registration to get id for new user. But after deletion of 21th row during nex registration process mysql_insert_id gave me number 21. but stored in 24th row. And put to associations table 21 for new user. I wanna solve this problem
When you use an autoincrement id column, the value that the next entry will be assigned will not be reduced by deleting an entry. That is not what an autoincrement column is used for. The database engine will always increment that number on a new insert and never decrement that number on a delete.
A MySQL auto_increment column maintains a number internally, and will always increment it, even after deletions. If you need to fill in an empty space, you have to handle it yourself in PHP, rather than use the auto_increment keyword in the table definition.
Rolling back to fill in empty row ids can cause all sorts of difficulty if you have foreign key relationships to maintain, and it really isn't advised.
The auto_increment can be reset using a SQL statement, but this is not advised because it will cause duplicate key errors.
-- Doing this will cause problems!
ALTER table AUTO_INCREMENT=12345;
EDIT
To enforce your foreign key relationships as described in the comments, you should add to your table definition:
FOREIGN KEY (friendid) REFERENCES registration_table (id) ON DELETE SET NULL;
Fill in the correct table and column names. Now, when a user is deleted from the registration, their friend association is nulled. If you need to reassociate with a different user, that has to be handled with PHP. mysql_insert_id() is no longer helpful.
If you need to find the highest numbered id still in the database after deletion to associate with friends, use the following.
SELECT MAX(id) FROM registration_table;
Auto increment is a sequence key that's tracked as part of the table. It does not go back when you delete a row.
Easily, no. What you can do (but I don't suggest doing) is making an SQL function to determine the lowest number that isn't currently occupied. Or you can create a table of IDs that were deleted, and get the smallest number from there. Or, and this is the best idea, ignore the gaps and realize the database is fine.
What you want to do is achievable by adding an extra column to your table called something like user_order. You can then write code to manage inserts and deletions so that this column is always sequential with no gaps.
This way you avoid the problems you could have messing around with an auto_increment column.
It's not a good practice to reset auto_increment value, but if you really need to do it, so you can:
ALTER TABLE mytable AUTO_INCREMENT = 1;
Run this query after every delete. Auto_increment value will not be set to 1, this will set the lowest possible value automatically.