I'm trying to write a SQL query that satisfies multiple criteria.
Of these, most are connected via a column, so joins are possible, however, some queries are such that I'd have to search additional tables for the information. What would be the least expensive and best way to do this?
Let's say that we have a few tables.
One table contains information such as sales information for a server: the salesperson, client id, service lease term, timestamps etc. It is possible that a client has multiple sales but with a different "service". I'd need to pick up all of the different ones.
Another table has the quotes for the services, I'd need to pick some information out about this, whilst another, which could be joined to this one has some more information.
Those tables are linked by a common client ID, so joins are possible, but I'd also need to search the first table for multiple instances of the client ID. Of course, I'd want to restrict the search to certain timestamps, which I can easily do as the timestamps are stored in MySQL format.
Related
So I am building a swingers site. The users can search other users by their interests. This is only part of a number of parameters used to search a user. The thing is there are like 100 different interests. When searching another user they can select all the interests the user must share. While I can think of ways to do this, I know it is important the search be as efficient as possible.
The backend uses jdbc to connect to a mysql database. Java is the backend programming language.
I have debated using multiple columns for interests but generating the thing is the sql query need not check them all if those columns are not addressed in the json object send to the server telling it the search criteria. Also I worry i may have to make painful modifications to the table at a later point if i add new columns.
Another thing I thought about was having some kind of long byte array, or number (used like a byte array) stored in a single column. I could & this with another number corresponding to the interests the user is searching for but I read somewhere this is actually quite inefficient despite it making good sense to my mind :/
And all of this has to be part of one big sql query with multiple tables joined into it.
One of the issues with me using multiple columns would be the compiting power used to run statement.setBoolean on what could be 40 columns.
I thought about generating an xml string in the client then processing that in the sql query.
Any suggestions?
I think the correct term is a Bitmask. I could maybe have one table for the bitmask that maps the users id to the bitmask for querying users interests, and another with multiple entries for each interest per user id for looking up which user has which interests efficiently if I later require this?
Basically, it would be great to have a separate table with all the interests, 2 columns: id and interest.
Then, have a table that links the user to the interests: user_interests which would have the following columns: id,user_id,interest_id. Here some knowledge about many-to-many relations would help a lot.
Hope it helps!
I have two tables in sql server 2012 as:
CropPurchase(Date,CropId,CustId,Qty,Price,Discount,Paid)
CropSale(Date,CropId,VendorId,Qty,Price,Discount,Paid)
By joining transactions of these two tables I have to fetch an account on front end(C# app), called:
CropAccount(Date,CropId,CustId,VendorId,DebitQty,CreditQty,DebitAmnt,CreditAmnt,Balance).
I have to order this table by Date.
So the Question is, that what should be the good practice:
To Create another table which will Contain mixed records of both the tables and fetch this table on front end.
Or to fetch record directly from the two tables to front end and not creating a third table.(it can create problem while ordering by Date).
This depends. Usually you have different tables to represent different entities. So you have zero, one or many CropPurchase records per CropId, and zero, one or many CropSale records per CropId. Two different entities. And to get the data per CropId you will have to join one or both tables and Aggregate when needed. So stay with the two tables and join when needed. (You can write a view for convenience, though.)
If however there can be no more than one record in CropPurchase and CropSale per CropId, then we are no langer really talking about two different entities. We are talking merely of the one crop account identified by CropId having purchase and sale data. Then you should have one table instead of two.
Anyway: Don't keep the two tables and add a third holding their data redundantly. That will lead to problems sooner or later.
Please elaborate on the date order problems you fear you'll be facing.
I've a mysql table "login" with columns name, userid, pass, email. and another table "info" with columns bio, skills, searchingfor, badge, likes, age
here, the 1st table is used to check login... and the rest is used for storing personal info of an user. but i have a search box where people can search user according to everything except bio & pass. I'm having problem joining the results from two tables so is it ok to put all in one table or is there a simplier way?
and if i put everything in a table would it be heavier for mysql queries to search if the database gets lots of data?
There is no higher load on your mysql server if you combine both tables. This is a valid idea, since it appears that you have a 1:1 relationship anyway, so the code get's easier. Actually the load will be lower, since you do not need a join which is actually very slow in relational database management systems. The performance (load) just depends on your indexes and filter requirements, but that is independent of whether you search in one or two tables.
On the other hand: there is no reason why you should not be able to join those tables as required. So maybe you want to solve your issue here first. And be it just to learn how to do do it ;-)
I'm building an stock exchange simulation game. I have a table called 'Market_data' and in the game players simulate being in particular dates and are allowed to use SQL queries to retrieve the historical data and plan their course of action. My difficulty is that I need to limit the rows they can access based on the current date they are playing on so they cant see rows with a date greater than the current date.
Eg: An user is running the game and is currently in the year 2010, if he does a simple select like "SELECT * FROM market_data" I don't want him to see rows with Date > 'x-x-2010'
The only soution that I know of is to parse the user's SQL and add WHERE clauses to remove newer dates but it seems time consuming and prone to errors and I wasn't sure whether there were better alternatives. Any ideas on how to do this right will be thanked.
Solution is SQL Views, Views are used for several different reasons:
*1.*To hide data complexity. Instead of forcing your users to learn the T-SQL JOIN syntax you might wish to provide a view that runs a commonly requested SQL statement.
*2.*To protect the data. If you have a table containing sensitive data in certain columns, you might wish to hide those columns from certain groups of users. For instance, customer names, addresses and their social security numbers might all be stored in the same table; however, for lower level employees like shipping clerks, you can create a view that only displays customer name and address. You can grant permissions to a view without allowing users to query the underlying tables. There are a couple of ways you might want to secure your data:
a.Create a view to allow reading of only certain columns from a table. A common example of this would be the salary column in the employee table. You might not want all personnel to be able to read manager's or each other's salary. This is referred to as partitioning a table vertically and is accomplished by specifying only the appropriate columns in the CREATE VIEW statement.
b.Create a view to allow reading only certain rows from a table. For instance, you might have a view for department managers. This way, each manager can provide raises only to the employees of his or her department. This is referred to as horizontal partitioning and is accomplished by providing a WHERE clause in the SELECT statement that creates a view.
*3.*Enforcing some simple business rules. For example, if you wish to generate a list of customers that need to receive the fall catalog, you can create a view of customers that have previously bought your shirts during the fall.
*4.*Data exports with BCP. If you are using BCP to export your SQL Server data into text files, you can format the data through views since BCP's formatting ability is quite limited.
*5.*Customizing data. If you wish to display some computed values or column names formatted differently than the base table columns, you can do so by creating views.
reference taken from http://sqlserverpedia.com.
1)You can use mysql proxy http://dev.mysql.com/downloads/mysql-proxy/ with custom rules restricting access.
2)You can use stored procedures/functions
3)You can use views
The basic way would be :
-> Prevent that user (or group) from accessing the base table.
-> Define a view on top of that table that shows only the rows these users are supposed to see.
-> Give those users SELECT permission on the view.
-> And you can also use SQL Encryption,Decryption and Hashing concept.
Encryption & Decryption examples can be found here:
http://msdn.microsoft.com/en-us/library/ms179331.aspx
Hashing example can be found here:
http://msdn.microsoft.com/en-us/library/ms174415.aspx
I want to try and keep this as one query and not use PHP, but it's proving to be tough.
I have a table called applications, that stores all the applications and some basic information about them.
Then, I have a table with all the types of applications in it, and that table contains a reference to another table which stores more specific data about the specific type of application in question.
select applications.id as appid, applications.category, type.title as type, type.id as tid, type.valuefld, type.tablename
from applications
left join type on applications.typeid=type.id
left join department on type.deptid=department.id
where not isnull(work_cat)
and work_cat != ''
and applications.deleted=0
and datei between '10-04-14' and '11-04-14'
order by type, work_cat
Now, in the old version, there is another query on every single result. Over hundreds of results... that sucks.
This is the query I'd like to integrate so I can get all the data in one result row. (Old is ASP, I'm re-writing it in PHP)
query = "select sum("&adors.fields("valuefld")&") as cost, description from "&adors.fields("tablename")&" where appid = '"&adors.fields("tablename")&"'"
Prepared statements, I'm aware, are the best solution, but for now they are not an option.
You can't do this with a plain SQL query - you need to have a defined set of tables that your query is based on. The fact that your current implementation queries from whatever table is named by tablename from the first result-set means that to get this all in one query, you will have to restructure your data. You have to know what tables you're querying from rather than having it dynamic.
If the reason for these different tables is the different information stored in each requiring different record (column) structures, you might want to look into Key/Value pair storage in a large table. Once you combine the dynamically named ones into a single location you can integrate your two queries together.