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• Thinking of an Inner Join as a Cross Join and then satisfying some condition(s)?

  - by Jian Lin

  It seems like the safest way to think of an Inner Join is to think of it as a Cross Join and then satisfying some condition(s)? Because the equi-join can be obvious, but the non-equi-join can be a bit confusing. But if we always use the Cross Join, and then filter out the ones satisfying the condition, then we get the resulting table. In other words, we can always analyze it by using the first record on the left table, and then go through every single records on the right, and then repeat that for 2nd record on the left, and for the 3rd, 4th, ... etc. So in our mind, we can analyze it using this way, and it is like O(n^2), although what happens in the DBMS maybe that it is a lot faster (when an index is present). Is there another good way to think of it besides this method?

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• Computed column should result to string

  - by strakastroukas

  Here is a snap of my database. Both col1 and col2 are declared as int. My ComputedColumn currently adds the Columns 1 and 2, as follows... col1 col2 ComputedColumn 1 2 3 4 1 5 Instead of this, my ComputedColumn should join the columns 1 and 2 (includimg the '-' character in the middle) as follows... col1 col2 ComputedColumn 1 2 1-2 4 1 4-1 So, what is the correct syntax?

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• LINQtoSQL: Query to return List<String>

  - by ctrlShiftBryan

  I have a LINQ query that returns some object like this... var query = from c in db.Customers where ... select c; Then I do this List<String> list = new List<String>(); foreach (ProgramLanguage c in query) { //GetUL returns a String list.Add(GetUL(c.Property,c.Property2)); } Is there a way to combine into something list this? var query = from c in db.Customers where ... select new { GetUL(c.Property,c.Property2) }).ToList<String>();

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• How can i get rid of 'ORA-01489: result of string concatenation is too long' in this query?

  - by core_pro

  this query gets the dominating sets in a network. so for example given a network A<----->B B<----->C B<----->D C<----->E D<----->C D<----->E F<----->E it returns B,E B,F A,E but it doesn't work for large data because i'm using string methods in my result. i have been trying to remove the string methods and return a view or something but to no avail With t as (select 'A' as per1, 'B' as per2 from dual union all select 'B','C' from dual union all select 'B','D' from dual union all select 'C','B' from dual union all select 'C','E' from dual union all select 'D','C' from dual union all select 'D','E' from dual union all select 'E','C' from dual union all select 'E','D' from dual union all select 'F','E' from dual) ,t2 as (select distinct least(per1, per2) as per1, greatest(per1, per2) as per2 from t union select distinct greatest(per1, per2) as per1, least(per1, per2) as per1 from t) ,t3 as (select per1, per2, row_number() over (partition by per1 order by per2) as rn from t2) ,people as (select per, row_number() over (order by per) rn from (select distinct per1 as per from t union select distinct per2 from t) ) ,comb as (select sys_connect_by_path(per,',')||',' as p from people connect by rn > prior rn ) ,find as (select p, per2, count(*) over (partition by p) as cnt from ( select distinct comb.p, t3.per2 from comb, t3 where instr(comb.p, ','||t3.per1||',') > 0 or instr(comb.p, ','||t3.per2||',') > 0 ) ) ,rnk as (select p, rank() over (order by length(p)) as rnk from find where cnt = (select count(*) from people) order by rnk ) select distinct trim(',' from p) as p from rnk where rnk.rnk = 1`

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• Linq ChangeConflictException (ASP.NET MVC) - occurs when submitting DataContext changes

  - by Alex

  System.Data.Linq.ChangeConflictException: 2 of X updates failed. at System.Data.Linq.ChangeProcessor.SubmitChanges(ConflictMode failureMode) at System.Data.Linq.DataContext.SubmitChanges(ConflictMode failureMode) at PROJECT.Controllers.HomeController.ClickProc(Int32 id, String code, String n) This is what I get very often. This action is done thousands of times a day, and I get this exception about once every 5 seconds. From what I understand it happens when something changes in the database in the period between creating DataContext and updating it. Am I right? What's the problem here and how can I fix it?

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• Are GUID primary keys bad in theory, or just practice?

  - by Yarin

  Whenever I design a database I automatically start with an auto-generating GUID primary key for each of my tables (excepting look-up tables) I know I'll never lose sleep over duplicate keys, merging tables, etc. To me it just makes sense philosophically that any given record should be unique across all domains, and that that uniqueness should be represented in a consistent way from table to table. I realize it will never be the most performant option, but putting performance aside, I'd like to know if there are philosophical arguments against this practice?

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• Can I join two tables whereby the joined table is sorted by a certain column?

  - by Ferdy

  I'm not much of a database guru so I need some help on a query I'm working on. In my photo community project I want to richly visualize tags by not only showing the tag name and counter (# of images inside them), I also want to show a thumb of the most popular image inside the tag (most karma). The table setup is as follow: Image table holds basic image metadata, important is the karma field Imagefile table holds multiple entries per image, one for each format Tag table holds tag definitions Tag_map table maps tags to images In my usual trial and error query authoring I have come this far: SELECT * FROM (SELECT tag.name, tag.id, COUNT(tag_map.tag_id) as cnt FROM tag INNER JOIN tag_map ON (tag.id = tag_map.tag_id) INNER JOIN image ON tag_map.image_id = image.id INNER JOIN imagefile on image.id = imagefile.image_id WHERE imagefile.type = 'smallthumb' GROUP BY tag.name ORDER BY cnt DESC) as T1 WHERE cnt > 0 ORDER BY cnt DESC [column clause of inner query snipped for the sake of simplicity] This query gives me somewhat what I need. The outer query makes sure that only tags are returned for which there is at least 1 image. The inner query returns the tag details, such as its name, count (# of images) and the thumb. In addition, I can sort the inner query as I want (by most images, alphabetically, most recent, etc) So far so good. The problem however is that this query does not match the most popular image (most karma) of the tag, it seems to always take the most recent one in the tag. How can I make sure that the most popular image is matched with the tag?

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• Arrays in database tables and normalization

  - by Ivan Petrov

  Hi! Is it smart to keep arrays in table columns? More precisely I am thinking of the following schema which to my understanding violates normalization: create table Permissions( GroupID int not null default(-1), CategoryID int not null default(-1), Permissions varchar(max) not null default(''), constraint PK_GroupCategory primary key clustered(GroupID,CategoryID) ); and this: create table Permissions( GroupID int not null default(-1), CategoryID int not null default(-1), PermissionID int not null default(-1), constraint PK_GroupCategory primary key clustered(GroupID,CategoryID) ); UPD: Forgot to mention, in the scope of this concrete question we will consider that the "fetch rows that have permission X" won't be performed, instead all the lookups will be made by GroupID and CategoryID only Thoughts? Thanks in advance!

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• Primary key/foreign Key naming convention

  - by Jeremy

  In our dev group we have a raging debate regarding the naming convention for Primary and Foreign Keys. There's basically two schools of thought in our group: 1) Primary Table (Employee) Primary Key is called ID Foreign table (Event) Foreign key is called EmployeeID 2) Primary Table (Employee) Primary Key is called EmployeeID Foreign table (Event) Foreign key is called EmployeeID I prefer not to duplicate the name of the table in any of the columns (So I prefer option 1 above). Conceptually, it is consisted with a lot of the recommended practices in other languages, where you don't use the name of the object in its property names. I think that naming the foreign key EmployeeID (or Employee_ID might be better) tells the reader that it is the ID column of the Employee Table. Some others prefer option 2 where you name the primary key prefixed with the table name so that the column name is the same throughout the database. I see that point, but you now can not visually distinguish a primary key from a foreign key. Also, I think it's redundant to have the table name in the column name, because if you think of the table as an entity and a column as a property or attribute of that entity, you think of it as the ID attribute of the Employee, not the EmployeeID attribute of an employee. I don't go an ask my coworker what his PersonAge or PersonGender is. I ask him what his Age is. So like I said, it's a raging debate and we go on and on and on about it. I'm interested to get some new perspective.

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• Little Employee/Shift timetable HELP!!!

  - by DAVID

  Morning Guys, I have the following tables: operator(ope_id, ope_name) ope_shift(ope_id, shift_id, shift_date) shift(shift_id, shift_start, shift_end) here is a better view of the data http://latinunit.net/emp_shift.txt here is the screenshot of a select statement to the tables http://img256.imageshack.us/img256/4013/opeshift.jpg im using this code SELECT OPE_ID, COUNT(OPE_ID) AS Total_shifts from operator_shift group by ope_id; to view the current total shifts per operator and it works, BUT if there was 500 more rows it would count them all aswell, THE QUESTION is, anyone has a better way of making my database work, or how can i tell the system that those rows are a whole month, i remember i friend said something about count then devide by 30 but im not sure, what if the month isnt finished? and you want to show the emp with highest shifts to date

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• Implementing a 1 to many relationship with SQLite

  - by Patrick

  I have the following schema implemented successfully in my application. The application connects desk unit channels to IO unit channels. The DeskUnits and IOUnits tables are basically just a list of desk/IO units and the number of channels on each. For example a desk could be 4 or 12 channel. CREATE TABLE DeskUnits (Name TEXT, NumChannels NUMERIC); CREATE TABLE IOUnits (Name TEXT, NumChannels NUMERIC); CREATE TABLE RoutingTable (DeskUnitName TEXT, DeskUnitChannel NUMERIC, IOUnitName TEXT, IOUnitChannel NUMERIC); The RoutingTable 'table' then connects each DeskUnit channel to an IOUnit channel. For example the DeskUnit called "Desk1" channel 1 may route to IOunit name "IOUnit1" channel 2, etc. So far I hope this is pretty straightforward and understandable. The problem is, however, this is a strictly 1 to 1 relationship. Any DeskUnit channel can route to only 1 IOUnit channel. Now, I need to implement a 1 to many relationship. Where any DeskUnit channel can connect to multiple IOUnit channels. I realise I may have to rearrange the tables completely, but I am not sure the best way to go about this. I am fairly new to SQLite and databases in general so any help would be appreciated. Thanks Patrick

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• How to save multiple column in database

  - by shamim

  I have a text file.I need to get data from this text file and show on grid , 1)After this user can update information from gridview, 2)Click on save button save data on database. Before clicking on button data don't save on database.How to do that?

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• How to upload excel files to database using linq?

  - by Krishnan

  My team working in asp.net projects Here we have to upload Excel contents to Database We are using linq Please help to do the same

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• stored procedure to find value in 2 columns out of 3

  - by user1510533

  I am putting in the samle date and i am supposed to do something similar what i am asking. I want to run a query that would pull values in any two columns out 3 if it has a 1 or if any one column has a 1 it will return just those results. However it should search all three columns and in any of the three columns where it found value as 1 it should return that result. Can anyone please help me with this. Thanks in advance. ID Patient Patient Name prio prio2 prio3 ------------------------------------------------- 1 101563 Robert Riley 1 1 1 2 101583 Cody Ayers 1 0 1 3 101825 Jason Lawler 0 0 1 4 101984 Dustin Lumis 1 0 0 5 102365 Stacy smith 1 0 0 6 102564 Frank Milon 1 0 0 7 102692 Thomas Kroning 1 0 0 8 102856 Andrew Philips 1 0 0 9 102915 Alice Davies 0 0 1 10 103785 Jon Durley 0 0 1 11 103958 Clayton Folsom 1 1 1 12 104696 Michelle Holsley 1 1 1 13 104983 Teresa Jones 1 0 1 14 105892 Betsy Prat 1 1 0 15 106859 Casey Ayers 1 1 0

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• Precision of Interval for PL/SQL Function value

  - by Gary

  Generally, when you specify a function the scale/precision/size of the return datatype is undefined. For example, you say FUNCTION show_price RETURN NUMBER or FUNCTION show_name RETURN VARCHAR2. You are not allowed to have FUNCTION show_price RETURN NUMBER(10,2) or FUNCTION show_name RETURN VARCHAR2(20), and the function return value is unrestricted. This is documented functionality. Now, I get an precision error (ORA-01873) if I push 9999 hours (about 400 days) into the following. The limit is because the default days precision is 2 DECLARE v_int INTERVAL DAY (4) TO SECOND(0); FUNCTION hhmm_to_interval return INTERVAL DAY TO SECOND IS v_hhmm INTERVAL DAY (4) TO SECOND(0); BEGIN v_hhmm := to_dsinterval('PT9999H'); RETURN v_hhmm; -- END hhmm_to_interval; BEGIN v_int := hhmm_to_interval; end; / and it won't allow the precision to be specified directly as part of the datatype returned by the function. DECLARE v_int INTERVAL DAY (4) TO SECOND(0); FUNCTION hhmm_to_interval return INTERVAL DAY (4) TO SECOND IS v_hhmm INTERVAL DAY (4) TO SECOND(0); BEGIN v_hhmm := to_dsinterval('PT9999H'); RETURN v_hhmm; -- END hhmm_to_interval; BEGIN v_int := hhmm_to_interval; end; / I can use a SUBTYPE DECLARE subtype t_int is INTERVAL DAY (4) TO SECOND(0); v_int INTERVAL DAY (4) TO SECOND(0); FUNCTION hhmm_to_interval return t_int IS v_hhmm INTERVAL DAY (4) TO SECOND(0); BEGIN v_hhmm := to_dsinterval('PT9999H'); RETURN v_hhmm; -- END hhmm_to_interval; BEGIN v_int := hhmm_to_interval; end; / Any drawbacks to the subtype approach ? Any alternatives (eg some place to change a default precision) ? Working with 10gR2.

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• How to get top 3 frequencies in MySQL?

  - by Amenhotep

  Hello, In MySQL I have a table called "meanings" with three columns: "person" (int), "word" (byte, 16 possible values) "meaning" (byte, 26 possible values). A person assigns one or more meanings to each word: person word meaning ------------------- 1 1 4 1 2 19 1 2 7 <-- second meaning for word 2 1 3 5 ... 1 16 2 Then another person, and so on. There will be thousands of persons. I need to find for each of the 16 words the top three meanings (with their frequencies). Something like: word 1: meaning 5 (35% of people), meaning 19 (22% of people), meaning 2 (13% of people) word 2: meaning 8 (57%), meaning 1 (18%), meaning 22 (7%) ... Is it possible to solve this with a single MySQL query? (If this problem is a classic one and has been answered elsewhere, I would appreciate if you could give me a link to the solution.) Thank you very much, ve

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• LINQ Query returns false when it should be true.

  - by deliriousDev

  I have the following LINQ query written by a former developer and it isn't working when it should. public bool IsAvailable(Appointment appointment) { var appointments = _appointmentRepository.Get; var shifts = _scheduleRepository.Get; var city = _customerRepository.Find(appointment.CustomerId).City ?? appointment.Customer.City; const int durationHour = 1; DateTime scheduledEndDate = appointment.ScheduledTime.Add(new TimeSpan(durationHour, 0, 0)); var inWorkingHours = shifts .Where(x => //Check if any available working hours x.Employee.City == city && x.ShiftStart <= appointment.ScheduledTime && x.ShiftEnd >= scheduledEndDate && //check if not booked yet !appointments .Where(a => (appointment.Id == 0 || a.Id != appointment.Id) && a.Employee.Id == x.Employee.Id && ( (a.ScheduledTime <= appointment.ScheduledTime && appointment.ScheduledTime <= EntityFunctions.AddHours(a.ScheduledTime, durationHour)) || (a.ScheduledTime <= scheduledEndDate && scheduledEndDate <= EntityFunctions.AddHours(a.ScheduledTime, durationHour)) )) .Select(a => a.Employee.Id) .Contains(x.Employee.Id) ); if (inWorkingHours.Any()) { var assignedEmployee = inWorkingHours.FirstOrDefault().Employee; appointment.EmployeeId = assignedEmployee.Id; appointment.Employee = assignedEmployee; return true; } return false; } The query is suppose to handle the following scenarios Given An Appointment With A ScheduledTime Between A ShiftStart and ShiftEnd time But Does not match any employees in same city - (Return true, Assign as "Unassigned") Given An Appointment With A ScheduledTime Between A ShiftStart and ShiftEnd time AND Employee for that shift is in the same city as the customer (Return True AND Assign to the employee) If the customer is NOT in the same city as an employee we assign the appointment as "Unassigned" as along as the scheduledTime is within an of the employees shift start/end times If the customer is in the same city as an employee we assign the appointment to one of the employees (firstOrdefault) and occupy that timeslot. Appointments CAN NOT overlap (Assigned Ones). Unassigned can't overlap each other. This query use to work (I've been told). But now it doesn't and I have tried refactoring it and various other paths with no luck. I am now on week two and just don't know where the issue in the query is or how to write it. Let me know if I need to post anything further. I have verified appointments, shifts, city all populate with valid data so the issue doesn't appear to be with null or missing data.

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• Simple Database normalization question...

  - by user365531

  Hi all, I have a quick question regarding a database that I am designing and making sure it is normalized... I have a customer table, with a primary key of customerId. It has a StatusCode column that has a code which reflects the customers account status ie. 1 = Open, 2 = Closed, 3 = Suspended etc... Now I would like to have another field in the customer table that flags whether the account is allowed to be suspended or not... certain customers will be automatically suspended if they break there trading terms... others not... so the relevant table fields will be as so: Customers (CustomerId(PK):StatusCode:IsSuspensionAllowed) Now both fields are dependent on the primary key as you can not determine the status or whether suspensions are allowed on a particular customer unless you know the specific customer, except of course when the IsSuspensionAllowed field is set to YES, the the customer should never have a StatusCode of 3 (Suspended). It seems from the above table design it is possible for this to happen unless a check contraint is added to my table. I can't see how another table could be added to the relational design to enforce this though as it's only in the case where IsSuspensionAllowed is set to YES and StatusCode is set to 3 when the two have a dependence on each other. So after my long winded explanation my question is this: Is this a normalization problem and I'm not seeing a relational design that will enforce this... or is it actually just a business rule that should be enforced with a check contraint and the table is in fact still normalized. Cheers, Steve

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• Extending Zend DB Table to include BETWEEN and LIMIT.

  - by davykiash

  Am looking for how I can extend the Zend_DB_Table below to accomodate a BETWEEN two dates syntax and LIMIT syntax My current construct is class Model_DbTable_Tablelist extends Zend_Db_Table_Abstract { protected $_name = 'mytable'; $select = $this->select() ->setIntegrityCheck(false) ->from('mytable', array('MyCol1', 'MyDate')); } I want it extended to be equivalent to the query below SELECT MyCol1,MyDate FROM mytable WHERE MyDate BETWEEN '2008-04-03' AND '2009-01-02' LIMIT 0,20 Any ideas?

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• Problem with mysql query to replace a string

  - by alex

  I've used mysql's update replace function before, but even though I think I'm following the same syntax, I can't get this to work. Here's what I'm trying to do: UPDATE contained_widgets SET preference_values = REPLACE(preference_values, '<li><a_href="/enewsletter"><span class="not-tc">eNewsletter</span></a></li>', '<li><a_href="/enewsletter"><span class="not-tc">eNewsletter</span></a></li> <li> <a_href="/projects"><span class="not-tc">Projects</span></a></li>'); Query OK, 0 rows affected (0.00 sec) Rows matched: 77 Changed: 0 Warnings: 0 I don't see what I'm missing. Any help is appreciated. I edited "a " to "a_" because the site thinks I'm posting spam links otherwise.

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• How to avoid timestamp issue in a long query?

  - by pingi

  Hi, I have the following 2 tables: items: id int primary key bla text events: id_items int num int when timestamp without time zone ble text composite primary key: id_items, num and want to select to each item the most recent event (the newest 'when'). I wrote an request, but I don't know if it could be written more efficiently. Also on PostgreSQL there is a issue with comparing Timestamp objects: 2010-05-08T10:00:00.123 == 2010-05-08T10:00:00.321 so I select with 'MAX(num)' Any thoughts how to make it better? Thanks. SELECT i.*, ea.* FROM items AS i JOIN ( SELECT t.s AS t_s, t.c AS t_c, max(e.num) AS o FROM events AS e JOIN ( SELECT DISTINCT id_item AS s, MAX(when) AS c FROM events GROUP BY s ORDER BY c ) AS t ON t.s = e.id_item AND e.when = t.c GROUP BY t.s, t.c ) AS tt ON tt.t_s = i.id JOIN events AS ea ON ea.id_item = tt.t_s AND ea.cas = tt.t_c AND ea.num = tt.o;

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• Are there more secure alternatives to the .Net SQLConnection class?

  - by KeyboardMonkey

  Hi SO people, I'm very surprised this issue hasn't been discussed in-depth: This article tells us how to use windbg to dump a running .Net process strings in memory. I spent much time researching the SecureString class, which uses unmanaged pinned memory blocks, and keeps the data encrypted too. Great stuff. The problem comes in when you use it's value, and assign it to the SQLConnection.ConnectionString property, which is of the System.String type. What does this mean? Well... It's stored in plain text Garbage Collection moves it around, leaving copies in memory It can be read with windbg memory dumps That totally negates the SecureString functionality! On top of that, the SQLConnection class is non-inheritable, I can't even roll my own with a SecureString property instead; Yay for closed-source. Yay. A new DAL layer is in progress, but for a new major version and for so many users it will be at least 2 years before every user is upgraded, others might stay on the old version indefinitely, for whatever reason. Because of the frequency the connection is used, marshalling from a SecureString won't help, since the immutable old copies stick in memory until GC comes around. Integrated Windows security isn't an option, since some clients don't work on domains, and other roam and connect over the net. How can I secure the connection string, in memory, so it can't be viewed with windbg?

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• What's faster? select [object] or select new {[object].value1, [object].value2} with linq

  - by Darcy

  I was hoping some of you guru's out there know the answer to this question. Which is faster? A or B A: var item = from d in database select d; B: var item = from d in database select new {d.item1, d.item2}; SEEMINGLY, it seems like selecting part of the table object would be faster than selecting the entire object, but something tells me its not necessarily the case.

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• Postgresql Altering Table

  - by Jahn

  Is it possible to alter a table to add a new column and make that column a foreign key to another table in a single command in Postgresql? "alter table x add column y id references z(id)" doesn't seem to work as I had hoped.

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• Copying a subset of data to an empty database with the same schema

  - by user193655

  I would like to export part of a database full of data to an empty database. Both databases has the same schema. I want to maintain referential integrity. To simplify my cases it is like this: MainTable has the following fields: 1) MainID integer PK 2) Description varchar(50) 3) ForeignKey integer FK to MainID of SecondaryTable SecondaryTable has the following fields: 4) MainID integer PK (referenced by (3)) 5) AnotherDescription varchar(50) The goal I'm trying to accomplish is "export all records from MainTable using a WHERE condition", for example all records where MainID < 100. To do it manually I shuold first export all data from SecondaryTable contained in this select: select * from SecondaryTable ST outer join PrimaryTable PT on ST.MainID=PT.MainID then export the needed records from MainTable: select * from MainTable where MainID < 100. This is manual, ok. Of course my case is much much much omre complex, I have 200+ tables, so donig it manually is painful/impossible, I have many cascading FKs. Is there a way to force the copy of main table only "enforcing referntial integrity". so that my query is something like: select * from MainTable where MainID < 100 WITH "COPYING ALL FK sources" In this cases also the field (5) will be copied. ====================================================== Is there a syntax or a tool to do this? Table per table I'd like to insert conditions (like MainID <100 is only for MainTable, but I have also other tables).

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