Is there a way to auto increment entries to a MySQL table based on the value of another column in the inserted row? For example, something to say that this is the fifth entry for a specific username?
I know I could do a row count after I make my query, but that's not what I'm looking for. I've looked around and just can't seem to find anything on this.
Thanks!
Assuming that you have a table Users with 2 columns, username and counter. Example code for the case you mentioned. Run this to create the trigger. It should fire on every insert.
CREATE TRIGGER insert_update BEFORE INSERT ON Users
FOR EACH ROW
BEGIN
DECLARE name_count INTEGER;
SELECT COUNT(*) INTO #name_count FROM Users WHERE username = NEW.username;
INSERT INTO Users VALUES (NEW.username, #name_count+1);
END
END
Disclaimer: this might not be the most efficient or cleanest thing in the world. I would be interested in what the other folks can come up with.
Related
I am trying to develop a system to assign room numbers to tenants of a hostel upon registration, using the auto increment feature of sql.
However, it automatically increases by one after every entry. Because the hostel accommodates four people in one room, I want to change this to 4, so that after every 4 entries I get only one id/room number.
How do I go about this? I am using php and sql. If the autoincrement feature is not possible can you please suggest another way to achieve this? Thanks.
You would need:
http://dev.mysql.com/doc/refman/5.1/en/replication-options-master.html#sysvar_auto_increment_increment
It works like this:
mysql> SET ##auto_increment_increment=4;
So when you insert 4 rows, the auto increment column will be:
4,8,12,16
as best of my knowledge you cannot change the steps of auto-increment field. I suggest add another field and write a trigger to update its value based on auto-increment field (auto-increment/4).
I don't think this is possible with autoincrement..
Maybe you can do something like this:
//Pseudo code
//First you get the count of the highest id, to see how many users are in the last room.
SELECT COUNT(*) FROM table WHERE id=(SELECT id FROM table ORDER BY id DESC LIMIT 1)
//If the result of the last query is >= 4 then insert the next customer with id +1
Don't use auto_increment for this - it can't handle a situation where multiple records will share the same number and although you can reset it manually (see below) it's also not designed for a situation where numbers may get reused in a random order.
You could just have a room_number field with one of the mysql integer types (e.g. tinyint, smallint, mediumint…) or you could separate your database into two tables, one for people (each of whom have an id) and a second to map those ids to rooms.
However you do it, you'd then write a select query to check which room numbers are available before you add the person's details to the database.
You may need to read up on relational databases if that doesn't sound very clear.
If you do need to reset the auto_increment (sometimes it's nice to do it if you've filled a database with test data which you're about to wipe, and you want the real "production" data to begin at 1) you can use:
ALTER TABLE [tablename] AUTO_INCREMENT = 1
https://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html
Hello I have a mysql database and all I want is basically to get a value on the second table from a first table query
I have figured something like this but is not working.
select src, dst_number, state, duration
from cdrs, area_code_infos
where SUBSTRING(cdrs.src,2,3) = area_code_infos.`npa`;
Please help me figure out this. I have tried in PHP to have multiple queries running one after the other but when I loaded the page after 45 minutes of wait time I gave up.
Thanks,
I assume the tables are farily big, and you are also doing an unindexed query.. basically substring has to be calculated for every row.
Whenever you do a join, you want to make sure both of the joined fields are indexed.
An option would be to create another column containing the substring calculation and then creating an index on that.
However, a better option would be to have an areaCodeInfosID column and set it as a foreign key to the area_code_infos table
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.
please with respect to username and storetype, how can I merge rows to achieve Final table? storetype should be unique per username. There are thousands of usernames and records so php/mysql would help.
thanks
Since only the storetype matter, just run through the table for every username storing the details in variables which are not null. After that run an alter table command to update only one row with these values in the variables and then delete the other rows.
You could also use certain Normalization rules to first break up the table and rejoin them back up again. It could be less efficient though.
select min(id), username, min(filename), min(date), min(desc), storetype,
min(password), min(email), min(ftp)
from table1
group by username, storetype
thanks to #Mosty Mostacho
I have to insert data into two tables, Items and Class_Items. (A third table, Classes is related here, but is not being inserted into).
The primary key of Items is Item_ID, and it's an auto-incrementing integer. Aside from this primary key, there are no unique fields in Items. I need to know what the Item_ID is to match it to Classes in Class_Items.
This is all being done through a PHP interface. I'm wondering what the best way is to insert Items, and then match their Item_ID's into Class_Items. Here are the two main options I see:
INSERT each Item, then use mysql_insert_id() to get its Item_ID for the Class_Items INSERT query. This means one query for every Item (thousands of queries in total).
Get the next Autoincrement ID, then LOCK the Class_Items table so that I can just keep adding to an $item_id variable. This would mean just two queries (one for the Items, one for the Class_Items)
Which way is best and why? Also, if you have an unlisted alternative I'm open to whatever is most efficient.
The most efficient is probably going to be to use parameterized queries. That would require using the mysqli functions, but if you're to the point of needing to optimize this kind of query you should think about being there anyway.
No matter how you cut it, you've got two inserts to make. Doing the first, grabbing the new ID value as you've described (which imposes insignificant overhead, because the value is on hand to mysql already,) and using it in the second insert is pretty minimal.
I would investigate using stored procedures and/or transactions to make sure nothing bad happens.
I'm working on a project with mysql and what I did is the following (without using autoincrement fields):
1- I created a table called SEQUENCE with one field of type BIGINT called VALUE with an initial value of 1. This table will store the id value that will be incremented each time you insert a new record.
2- Create a store procedure and handle the id increment inside it within a transaction.
Here is an example.
CREATE PROCEDURE `SP_registerUser`(
IN _username VARCHAR(40),
IN _password VARCHAR(40),
)
BEGIN
DECLARE seq_user BIGINT;
START TRANSACTION;
#Validate that user does not exist etc..........
#Register the user
SELECT value FROM SEQUENCE INTO seq_user;
UPDATE SECUENCE SET value = value + 1;
INSERT INTO users VALUES(seq_user, _username, SHA1(_password));
INSERT INTO user_info VALUES(seq_user, UTC_TIMESTAMP());
COMMIT;
END //
In my case I want to store the user id in two different tables (users and user_info)