So at my job ive been asked to fix some sql code running on mysql 5 database and im stuck, also im not sure if this is the right place to do this but there is a small beer bounty on this question. Well send the top voted question some beer monies.
Basically the statement needs to do the following:
Delete the row from customers_basket where products.products_quantity < 1 AND LOWER(inventory_t_product_minimum_stock.minimum_quantity) = 'nla'
This is the current statement:
DELETE FROM customers_basket
WHERE EXISTS
(SELECT products_id
FROM inventory_t_product_minimum_stock
WHERE customers_basket.products_id =
inventory_t_product_minimum_stock.products_id
AND LOWER(inventory_t_product_minimum_stock.minimum_quantity) = 'nla')
So really all that needs to change is add the bit about products_quantity < 1 however, that information comes from a different table.
Writing a simple left join for 3 tables wouldn't be difficult, my concern however is that this code is executed when the user logs in and joining three large tables would be a pretty big issue for us i imagine. Im actually a C developer come javascript coder some dbs are a little outside my area of expertise. Would one of the sql gurus out there have a good solution with out having to change our db schema?
edit* spelling
As long as your tables are properly indexed, and you're joining on the indexed fields, and your filters are targeting an indexed field, the query should perform fairly well.
Also, are you only deleting items in the customer basket table for the user logging in or for all products that have a quantity of < 1?
Related
I am trying to update a table with a column from another table. I dont want to view the join, I want to alter the table.
However, this is faiing:
UPDATE
a_dataset
SET
a_dataset.lang_flag = b_dataset.language
FROM
a_dataset
INNER JOIN
b_dataset
ON
a_dataset.ID = b_dataset.ID
However, I keep getting a syntax error, and cannot locate what I am missing?
I am guessing that you mean to update your records when you say alter the table. If so, you can simply rewrite your update statement with join like this:
UPDATE a_dataset a
JOIN b_dataset b ON a.ID = b.ID
SET a.lang_flag = b.[LANGUAGE]
As Uueerdo and myself said: Starting table names with numbers is a bad[TM] idea. The same is for letters, which you now chose to use. a is no better than 1 in this regard. Also calling tables just "dataset" isn't really helpful either. What is the table storing? Users? Then call it users. Articles on a news web site? Then call it articles. And so on. Everything in a database is dataset, no need to tell that anyone.
I guess you're new to SQL, am I right? Because another issue is: Unless you're going to drop table b_dataset after this command, you're probably doing something you're not supposed to do in relational data bases. The whole idea is to store all data only once. If you can automagically copy the column from b to a, then you could also select join if from a and b when you need it instead of copying it.
For learning SQL (or anything else), Stack Overflow is probably a bad place (it's good for asking questions in the process, though), so I recommend that you go get someone who has some experience in SQL to teach you, or get some book / tutorial on SQL. From first glance, this seems to be a good on-line book: http://sql.learncodethehardway.org/ - but I didn't read it.
I'm busy looking at building a matchmaking (dating-) site. The tables and queries are set up in a way i'm not happy with. It's still under construction so i'm happy to change anything in order to get it to work properly. It was very speedy until i decided to fill the database with loads of records to see how it performs.
Beware, this is a rather long post with lots (i hope the right...) information.
I have been googling' and reading in books for days now but A) the query performs very slowly (no wonder, it's no good i think) and B) i'm not getting any further with it.
So i hope somebody can help me to tell me what i'm doing wrong, what i should be doing and how to speed the query up. It's taking as long as 10-20 seconds to generate a result set and thats not good, anybody knows..
The information:
I have a table called 'profiles' with about 500.000 records in it. (at this time, could be more in the future)
Profiles table:
example contents:
Every answer to a question gets inserted to the profiles table, as a row. There are questions who are multiple choice so every answer selected by the member will be inserted as a new row in the profiles table and there are questions which can only have one answer thus one row in the profiles table.
Also, there is the table 'status' in which i keep record of members blocking or favoriting each other:
example contents:
Once the member fills in his/her criteria, php dynamically builds the query which needs to fetch records from the profiles table:
You can imagine how big this select query will get if all 90 questions are in the sql statement above..
Explain tells me this:
Basically i want to query the profiles table, fetching members matching the given criteria. The criteria are:
the criteria that the member who searches entered as his/hers will retrieve matching members as a result
the current member (the one who searches) should not be in the result(s)
members who are present in the status table with a status of 'block' should not be in the result(s)
I'm aware (now) that the 'where in' clauses are not very fast, the indexes could be wrong and the maybe my whole table lay-out needs to be different, but i hope somebody can either point me or help me in the right direction. After a day of trying and googling' i'm at my wits end.
If you need more information, just shout! Hopefully somebody can help me.
I'm writing an application to allow users to create a Poll. They ask a question and set n number of predefined answers to the question. Other users can vote on the answers provided for that question.
Current structure
I have designed the database like this:
Storing the vote count
Current thinking is, I create a new column called vote_count on the link table and every time that answer gets voted, it updates the record.
This works. But is it right? I'm new to database systems, so I can't imagine I'm doing much right. What are some more efficient ways to achieve this?
As far as it goes yes that's OK. However these tables will be incomplete. When your second quiz is created, you'll have to extend the QUESTIONS table. If this second quiz's Q1 also has a yes/no answer, you're going to have to extend the LINK/VOTES table.
You also have to think about how it's going to be queried and design indexes to support those queries.
Cheers -
I've been trying to get this SQL query running for a while now and can't seem to get the last little bit going.
The backend database to all this data is a Drupal install with data spread out across a number of modules, so I need to do a lot of joining to get a certain view table set up that I need for a third-party application.
It's hard to explain the entire schema, but here's the sqlfiddle:
http://sqlfiddle.com/#!2/68df0/2/0
So basically, I have a userid which I map to a profile id through a join. Then I need to use that profile ID to pull the related data about that profile from two other tables. (there should only be one row with each pid in each of the other tables)
So in the end, I would like to see a table with username, othername, and key_id.
I got the first two pieces in there, but just can't seem to figure out how to join in the othername, and keep getting null.
The server is running MySQL.
Thanks guys!
LEFT JOIN other_name
ON profile_link.pid=other_name.pid;
I am making a database that is for employee scheduling. I am, for the first time ever, making a relational mySQL database so that I can efficiently manage all of the data. I have been using the mySQL Workbench program to help me visualize how this is going to go. Here is what I have so far:
What I have pictured in my head is that, based on the drawing, I would set the schedule in the schedule table which uses references from the other tables as shown. Then when I need to display this schedule, I would pull everything from the schedule table. Whenever I've worked with a database in the past, it hasn't been of the normalized type, so I would just enter the data into one table and then pull the data out from that one table. Now that I'm tackling a much larger project I am sure that having all of the tables split (normalized) like this is the way to go, but I'm having trouble seeing how everything comes together in the end. I have a feeling it doesn't work the way I have it pictured, #grossvogel pointed out what I believe to be something critical to making this all work and that is to use the join function to pull the data.
The reason I started with a relational database was so that if I made a change to (for example) the shift table and instead of record 1 being "AM" I wanted it to be "Morning", it would then automatically change the relevant sections through the cascade option.
The reason I'm posting this here is because I am hoping someone can help fill in the blanks and to point me in the right direction so I don't spend a lot of hours only to find out I made a wrong turn at the beginning.
Maybe the piece you're missing is the idea of using a query with joins to pull in data from multiple tables. For instance (just incorporating a couple of your tables):
SELECT Dept_Name, Emp_Name, Stat_Name ...
FROM schedule
INNER JOIN departments on schedule.Dept_ID = departments.Dept_ID
INNER JOIN employees on schedule.Emp_ID = employees.Emp_ID
INNER JOIN status on schedule.Stat_ID = status.Stat_ID
...
where ....
Note also that a schedule table that contains all of the information needed to be displayed on the final page is not in the spirit of relational data modeling. You want each table to model some entity in your application, so it might be more appropriate to rename schedule to something like shifts if each row represents a shift. (I usually use singular names for tables, but there are multiple perspectives there.)
This is, frankly, a very difficult question to answer because you could get a million different answers, each with their own merits. I'd suggest you take a look at these (there are probably better links out there too, these just seemed like good points to note) :
http://www.devshed.com/c/a/MySQL/Designing-a-MySQL-Database-Tips-and-Techniques/
http://en.wikipedia.org/wiki/Boyce%E2%80%93Codd_normal_form
http://www.sitepoint.com/forums/showthread.php?66342-SQL-and-RDBMS-Database-Design-DO-s-and-DON-Ts
I'd also suggest you try explaining what it is you want to achieve in more detail rather than just post the table structure and let us try to figure out what you meant by what you've done.
Often by trying to explain something verbally you may come to the realisations you need without anyone else's input at all!
One thing I will mention is that you don't have to denormalise a table to report certain values together, you should be considering views for that kind of thing...