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  • Should I specify both INDEX and UNIQUE INDEX?

    - by Matt Huggins
    On one of my PostgreSQL tables, I have a set of two fields that will be defined as being unique in the table, but will also both be used together when selecting data. Given this, do I only need to define a UNIQUE INDEX, or should I specify an INDEX in addition to the UNIQUE INDEX? This? CREATE UNIQUE INDEX mytable_col1_col2_idx ON mytable (col1, col2); Or this? CREATE UNIQUE INDEX mytable_col1_col2_uidx ON mytable (col1, col2); CREATE INDEX mytable_col1_col2_idx ON mytable (col1, col2);

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  • Hash of unique value = unique hash?

    - by Nebs
    Theoretically does hashing a unique value yield a unique value? Let's say I have a DB table with 2 columns: id and code. id is an auto-incrementing int and code is a varchar. If I do ... $code = sha1($id); ... and then store $code into the same row as $id. Will my code column be unique as well? What about if I append the current time? eg: $code = sha1($id . time()); Thanks.

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  • Unique Business Value vs. Unique IT

    - by barry.perkins
    When the age of computing started, technology was new, exciting, full of potential and had a long way to grow. Vendor architectures were proprietary, and limited in function at first, growing in capability and complexity over time. There were few if any "standards", let alone "open standards" and the concepts of "open systems", and "open architectures" were far in the future. Companies employed intelligent, talented and creative people to implement the best possible solutions for their company. At first, those solutions were "unique" to each company. As time progressed, standards emerged, companies shared knowledge, business capability supplied by technology grew, and companies continued to expand their use of technology. Taking advantage of change required companies to struggle through periodic "revolutionary" change cycles, struggling through costly changes that were fraught with risk, resulted in solutions with an increasingly shorter half-life, and frequently required altering existing business processes and retraining employees and partner businesses. The pace of technological invention and implementation grew at an ever increasing rate, making the "revolutionary" approach based upon "proprietary" or "closed" architectures or technologies no longer viable. Concurrent with the advancement of technology, the rate of change in business increased, leading us to the incredibly fast paced, highly charged, and competitive global economy that we have today, where the most successful companies are companies that are good at implementing, leveraging and exploiting change. Fast forward to today, a world where dramatic changes in business and technology happen continually, a world where "evolutionary" change is crucial. Companies can no longer afford to build "unique IT", nor can they afford regular intervals of "revolutionary" change, with the associated costs and risks. Human ingenuity was once again up to the task, turning technology into a platform supporting business through evolutionary change, by employing "open": open standards; open systems; open architectures; and open solutions. Employing "open", enables companies to implement systems based upon technology, capability and standards that will evolve over time, providing a solid platform upon which a company can drive business needs, requirements, functions, and processes down into the technology, rather than exposing technology to the business, allowing companies to focus on providing "unique business value" rather than "unique IT". The big question! Does moving from "older" technology that no longer meets the needs of today's business, to new "open" technology require yet another "revolutionary change"? A "revolutionary" change with a short half-life, camouflaging reality with great marketing? The answer is "perhaps". With the endless options available to choose from, it is entirely possible to implement a solution that may work well today, but in 5 years time will become yet another albatross for the company to bear. Some solutions may look good today, solving a budget challenge by reducing cost, or solving a specific tactical challenge, but result in highly complex environments, that may be difficult to manage and maintain and limit the future potential of your business. Put differently, some solutions might push today's challenge into the future, resulting in a more complex and expensive solution. There is no such thing as a "1 size fits all" IT solution for business. If all companies implemented business solutions based upon technology that required, or forced the same business processes across all businesses in an industry, it would be extremely difficult to show competitive advantage through "unique business value". It would be equally difficult to "evolve" to meet or exceed business needs and keep up with today's rapid pace of change. How does one ensure that they do not jump from one trap directly into another? Or to put it positively, there are solutions available today that can address these challenges and issues. How does one ensure that the buying decision of today will serve the business well for years into the future? Intelligent & Informed decisions - "buying right" In a previous blog entry, we discussed the value of linking tactical to strategic The key is driving the focus to what is best for your business, handling today's tactical issues while also aligning with a roadmap/strategy that is tightly aligned with your strategic business objectives. When considering the plethora of possible options that provide various approaches to solving today's complex business problems, it is extremely important to ensure that vendors supplying those options, focus on what is best for your business, supplying sufficient information, providing adequate answers to questions, addressing challenges, issues, concerns and objections honestly and openly, and focus on supplying solutions that are tailored for, and deliver the most business value possible for your business. Here are a few questions to consider relative to the proposed options that should help ensure that today's solution doesn't become tomorrow's problem. Do the proposed solutions: Solve the problem(s) you are trying to address? Provide a solid foundation upon which to grow/enhance your business? Provide tactical gains that align with and enable your strategic business goals/objectives? Provide an infrastructure that can be leveraged with subsequent projects? Solve problems for the business overall, the lines of business, or just IT? Simplify your current environment Provide the basis for business: Efficiency Agility Clarity governance, risk, compliance real time business visibility and trend analysis Does your IT staff have the knowledge/experience to successfully manage the proposed systems once they are deployed in production? Done well, you will be presented with options tailored to your business, that enable you to drive the "unique business value" necessary to help your business stand out from others, creating a distinct competitive advantage, delivering what your customers need, when they need it, so you can attract new customers, new business, and grow top line revenue, all at a cost that provides a strong Return on Investment/Return on Assets. The net result is growth with managed cost providing significantly improved profit margin and shareholder value.

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  • How to set two column unique in SQL.

    - by sxingfeng
    I am creating a table ,in the table two column is unique, I mean columnA and columnB do not have same value: such as : Table X A B 1 2(RIGHT,unique) 2 2(RIGHT, unique) 1 3(RIGHT, not unique) 2 3(RIGHT, not unique) 1 2 (WRONG, not unique) How to create such a table? many thanks!

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  • unique constraint (w/o Trigger) on "one-to-many" relation

    - by elgcom
    To illustrate the problem, I make an example: A tag_bundle consists of one or more than one tags. A unique tag combination can map to a unique tag_bundle, vice versa. tag_bundle tag tag_bundle_relation +---------------+ +--------+ +---------------+--------+ | tag_bundle_id | | tag_id | | tag_bundle_id | tag_id | +---------------+ +--------+ +---------------+--------+ | 1 | | 100 | | 1 | 100 | +---------------+ +--------+ +---------------+--------+ | 101 | | 1 | 101 | +--------+ +---------------+--------+ There can't be another tag_bundle having the combination from tag 100 and tag 101. How can I ensure such unique constraint when executing SQL "concurrently"!! that is, to prevent concurrently adding two bundles with the same tag combination Adding a simple unique constraint on any table does not work, Is there any solution other than Trigger or explicit lock. I come to only this simple way: make tag combination into string, and let it be unique. tag_bundle (unique on tags) tag tag_bundle_relation +---------------+--------+ +--------+ +---------------+--------+ | tag_bundle_id | tags | | tag_id | | tag_bundle_id | tag_id | +---------------+--------+ +--------+ +---------------+--------+ | 1 | 100,101| | 100 | | 1 | 100 | +---------------+--------+ +--------+ +---------------+--------+ | 101 | | 1 | 101 | +--------+ +---------------+--------+ but it seems not a good way :(

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  • Creating a short unique string for each unique long string

    - by king.net
    I'm trying to create a url shortener system in c# and asp.net mvc. I know about hashtable and I know how to create a redirect system etc. The problem is indexing long urls in database. Some urls may have up to 4000 character length, and it seems it is a bad idea to index this kind of strings. The question is: How can I create a unique short string for each url? for example MD5 can help me? Is MD5 really unique for each string? NOTE: I see that Gravatar uses MD5 for emails, so if each email address is unique, then its MD5 hashed value is unique. Is it right? Can I use same solution for urls?

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  • mysql unique-constraint

    - by Cypher
    I have two tables -- Variables (id, name) and Variable_Entries (id, var_id, value). I want each variable to have a unique set of entries. If I make the value entry unique then a different variable won't be able to have that same value which is not right. Is there some way to make the value column unique for identical var_id's?

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  • UNIQUE Constraints in SQL (MS-SQL)

    - by rockbala
    Why are UNIQUE Constraints needed in database ? Can you provide any examples ? Primary Key is UNIQUE by default... Understandable as they are referred in other tables as Foreign keys... relation is needed to connect them for rdbms platform... but why would one refer to other columns as UNIQUE, what is benefit of doing so ?)

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  • UNIQUE Constraints in SQL (SQL Server)

    - by rockbala
    Why are UNIQUE Constraints needed in database ? Can you provide any examples ? Primary Key is UNIQUE by default... Understandable as they are referred in other tables as Foreign keys... relation is needed to connect them for rdbms platform... but why would one refer to other columns as UNIQUE, what is benefit of doing so ?)

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  • Filtering out unique rows in MySQL

    - by jpatokal
    So I've got a large amount of SQL data that looks basically like this: user | src | dst 1 | 1 | 1 1 | 1 | 1 1 | 1 | 2 1 | 1 | 2 2 | 1 | 1 2 | 1 | 3 I want to filter out pairs of (src,dst) that are unique to one user (even if that user has duplicates), leaving behind only those pairs belonging to more than one user: user | src | dst 1 | 1 | 1 1 | 1 | 1 2 | 1 | 1 In other words, pair (1,2) is unique to user 1 and pair (1,3) to user 2, so they're dropped, leaving behind only all instances of pair (1,1). Any ideas? The answers to the question below can find the non-unique pairs, but my SQL-fu doesn't suffice to handle the complication of requiring that they belong to multiple users as well. [SQL question] How to select non "unique" rows

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  • Primary Key Identity Value Increments On Unique Key Constraint Violation

    - by Jed
    I have a SqlServer 2008 table which has a Primary Key (IsIdentity=Yes) and three other fields that make up a Unique Key constraint. In addition I have a store procedure that inserts a record into the table and I call the sproc via C# using a SqlConnection object. The C# sproc call works fine, however I have noticed interesting results when the C# sproc call violates the Unique Key constraint.... When the sproc call violates the Unique Key constraint, a SqlException is thrown - which is no surprise and cool. However, I notice that the next record that is successfully added to the table has a PK value that is not exactly one more than the previous record - For example: Say the table has five records where the PK values are 1,2,3,4, and 5. The sproc attempts to insert a sixth record, but the Unique Key constraint is violated and, so, the sixth record is not inserted. Then the sproc attempts to insert another record and this time it is successful. - This new record is given a PK value of 7 instead of 6. Is this normal behavior? If so, can you give me a reason why this is so? (If a record fails to insert, why is the PK index incremented?) If this is not normal behavior, can you give me any hints as to why I am seeing these symptoms?

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  • Unique SMS sender id?

    - by Pascal
    Hello, I want to build an app that send SMS to people. However, I want my users to know that the SMS comes from the app and nothing else so they can't fake it. Is there a way to guarantee that the sender ID is unique to my app? It seems that sending a SMS by phone is with a unique SENDER ID for each phone number. But, from what I read, I don't think it is the case when sending a SMS through a web gateway. Is this correct? I am not an expert in mobile phone security. Of course, I am willing to pay the price for a unique sender id, if such thing is possible. Regards, Pascal

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  • R - find and calculate with unique combinations of values

    - by lecodesportif
    I would like to work with unique combinations of var1 and var2. foo <- data.frame(var1= c(1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4), var2=c(1, 1, 1, 1, 2, 2, 1, 1, 2, 2, 2, 2, 2, 3, 3)) As has been noted (+1 for answers), unique(foo) results in this: var1 var2 1 1 1 2 2 1 3 2 2 4 3 1 5 3 2 6 4 2 7 4 3 Based on the unique combinations, how do I get the number of occurrences of a var1 value and the sum (bla) of each var1 value's var2 values. The output could look like this: var1 n bla 1 1 1 1 2 2 2 3 3 3 2 3 4 4 2 5 edit: The question was too basic and probably duplicate so I extended it.

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  • SharePoint: Unique column values

    - by Anoop
    I Want to have only unique values in a SharePoin List. To achieve this I can use 'ItemAdding' event handler as mentioned in the below link. http://weblogs.asp.net/vikram/archive/2008/12/24/sharepoint-using-event-handler-to-make-a-column-unique.aspx Now I have a Doubt: Suppose that two user tries to add list Item in the list with the same column value(which requires unique value) at the same Time. will ItemAdding event would be fired at the same time for both call? If so then there is a possibility that two items having same value in the column. Please confirm.

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  • How to generate unique number of 12 digits?

    - by DanSogaard
    I'm working on an app that sends raw data to zebra printer and print out barcodes. And since every item has its own unique barcode, I need to define a variable that automatically generates unique number of 12 digits long. see example: printBar prnt = new printBar("123456789012"); Is there anyway to define a double variable and pass it to a function that return uniqely 12 digits number and pass it over again to the printBar class?. But how to make sure everytime you access it returns a unique value?. I also thought of another way, since am using MS Access db, I can create a column of AutoNumber datatype and assign it to Random, but you don't get the exact 12 digits required, sometimes it generates a value of 10 digits sometimes more or less.

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  • mysql create table help with unique

    - by Matt
    I'm trying to create a table, and can't figure out how to assign two columns to be unique.. I know how to alter a table thats already created, but how do you do it in the create.. im after a create if not exist col1 TEXT, col2 TEXT, col3 TEXT unique(col1, col2) ^very rough basic but you get the idea

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  • SQL Server: "Mostly-unique" index

    - by Ian Boyd
    In a table i want to ensure that only unique vales exist over the five-column key: Timestamp Account RatingDate TripHistoryKey EventAction ========= ======= ========== ============== =========== 2010511 1234 2010511 1 INSERT 2010511 1234 2010511 4 INSERT 2010511 1234 2010511 7 INSERT 2010511 1234 2010511 1 INSERT <---duplicate But i only want the unique constraint to apply between rows when EventAction is INSERT: Timestamp Account RatingDate TripHistoryKey EventAction ========= ======= ========== ============== =========== 2010511 1234 2010511 1 INSERT 2010511 1234 2010511 1 UPDATE 2010511 1234 2010511 1 UPDATE <---not duplicate 2010511 1234 2010511 1 UPDATE <---not duplicate 2010511 1234 2010511 1 DELETE <---not duplicate 2010511 1234 2010511 1 DELETE <---not duplicate 2010511 1234 2010511 1 INSERT <---DUPLICATE Possible?

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  • Determining if an unordered vector<T> has all unique elements

    - by Hooked
    Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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  • Determing if an unordered vector<T> has all unique elements

    - by Hooked
    Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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  • Doubt in action script for Flex: getting unique elements from an ArrayCollection

    - by Nirmal Singh Raja Reegan
    Hi, I have an ArrayCollection as mentioned below. private var initDG:ArrayCollection = new ArrayCollection([ {fact: "Order #2314", appName: "AA"}, {fact: "Order #2315", appName: "BB"} {fact: "Order #2316", appName: "BB"} ... {fact: "Order #2320", appName: "CC"} {fact: "Order #2321", appName: "CC"} ]); I want to populate a ComboBox with UNIQUE VALUES of "appName" field from the ArrayCollection initDG. <mx:ComboBox id="appCombo" dataProvider="{initDG}" labelField="appName"/> One method I could think is to loop through the Array objects and for each object check and push unique appName entries into another Array. Is there any better solution available?

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  • Unique items in Hibernate collections

    - by Rickard Lindberg
    I have defined a collection in Hibernate like this: ... public class Item { ... @ElementCollection List<Object> relatedObjects; } It creates a mapping table with colums item_id and object_id. The problem is that object_id seems to be unique. In other words I can not have two different items being related to the same object. But that is what I want. I would like the combination of item_id and object_id to be unique. How do I do that?

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  • Check For Duplicate Records VS try/catch Unique Key Constraint

    - by Jed
    I have a database table that has a Unique Key constraint defined to avoid duplicate records from occurring. I'm curious if it is bad practice to NOT manually check for duplicate records prior to running an INSERT statement on the table. In other words, should I run a SELECT statement using a WHERE clause that checks for duplicate values of the record that I am about to INSERT. If a record is found, then do not run the INSERT statement, otherwise go ahead and run the INSERT.... OR Just run the INSERT statement and try/catch the exception that may be thrown due to a Unique Key violation. I'm weighing the two perspectives and can't decide which is best- 1. Don't waste a SELECT call to check for duplicates when I can just trap for an exception VS 2. Don't be lazy by implementing ugly try/catch logic VS 3. ???Your thoughts here??? :)

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  • Rails uniqueness constraint and matching db unique index for null column

    - by Dave
    I have the following in my migration file def self.up create_table :payment_agreements do |t| t.boolean :automatic, :default => true, :null => false t.string :payment_trigger_on_order t.references :supplier t.references :seller t.references :product t.timestamps end end I want to ensure that if a product_id is specified it is unique but I also want to allow null so I have the following in my model: validates :product_id, :uniqueness => true, :allow_nil => true Works great but I should then add an index to the migration file add_index :payment_agreements, :product_id, :unique => true Obviously this will throw an exception when two null values are inserted for product_id. I could just simply omit the index in the migration but then there's the chance that I'll get two PaymentAgreements with the same product_id as shown here: Concurrency and integrity My question is what is the best/most common way to deal with this problem

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