I am using c# winforms-MySql Server.
I have 12 values and in every hour I need to select one value from that 12 value list. Timer can easily select the number.
But the problem is I have 5 Terminal where the software is to be installed.
They all will select a value from the list. The value can be same or different.
But I need the select same value for all the terminal. I don't have any client-server facility because any terminal can be open or closed at any time.
Can MySql select a value from a list in every hour without any c# code?
Any concept will be helpful. I don't need any code if you have a problem.
Thanks
A solution can be:
Create a Table with only 1 Column and 1 Row. It will contain, in the single cell, the current synchronized value;
Create a Timer in mySql. You can get some useful infos here;
The Timer makes a Stored Procedure to run;
That Stored Procedure updates the synchronized value;
All the Terminals query the database looking for that value, whenever and however you want: they will always retrieve the a synchronized value.
Related
I have a two table scenario with a typical parent / child relational setup:
tblGroup - idGroup (autonumber, PK); GroupName (Short Text), Rank (Number)
tblRange - idRange (autonumber, PK), idGroup (FK -> tblGroup.idGroup), RangeName (Short Text), Rank (Number)
What I am doing on the parent (tblGroup) table is using a data macro to add the rank using the BeforeChange event:
IF
IsInsert
SetField - Rank
- DMAX(Rank, [tblGroup])+1
This works nicely and I can happily use a parametized INSERT query to add rows to the table and not have to worry about duplicate ranks and so forth.
What I would like to be able to do but cannot figure out how, is to have a data macro do the same thing for the child (tblRange) table, with the rank being set to the new highest for the parent group the child record belongs to.
If I use the same DMAX approach as I have above I am supposed to be able to set a criteria as a third option, acting like a where clause, to limit the lookup / calculation. How can I refer to the specific idGroup I am working with in tblRange in the macro? I cannot seem to figure out how to reference the new records value for this in the macro.
Something like DMAX(Rank, [tblRange], ???How_to_refer_to_idGroup_Properly???)+1
Any help greatly appreciated
Cheers
The Frog
I figured out a way to do this. Thankyou caffeinated beverages!
The reason for the strange error messages is due to limitations in the Data Macro processing, specifically in the BeforeChange event. The solution is as follows:
Create a query that selects MAX rank (MaxRank) and GROUP BY for the idGroup (ParentID)
The resultant query produces two columns of data: [MaxRank] and [ParentID]
There will be a row for every idGroup with the maximum Rank for each
Create a BeforeChange data macro
Set the following:
IF IsInsert
LookupRecord
Lookup Record In - qryGetMaxRank (or whatever you called your query)
WHERE - [qryGetMaxRank].[ParentID] = [tblRange].[idGroup]
Set Field
Name - [tblRange].[Rank]
Value - [MaxRank] + 1
The BeforeChange event cannot handle parameters for a query, and I am guessing that this applies in some form the to DMAX function here too. The use of a query that does not use any parameters, and then using the LookupRecord WHERE clause to do the filtering provided the single row result needed. The [MaxRank] value from the returned result is then able to be used to set a new value for the field.
Bit of a workaround but it does allow someone to work with the data either through a form or through the datasheet view and not create a problem.
**In answer to if this is a multi-user DB - it is not. It is just me working with it. If / when the solution is scaled up to something requiring multi-user I will likely recreate the BE in SQL Server or MySQL and use stored procedures for all data I/O. Happy to keep Access as the FE and compile into an application (using the runtime for clients), but I am a fair way off from having to do that yet. Very early stages of development at this time.
Cheers to everyone for the pointers. They helped me figure this out. Hopefully this will be of use to someone else in the future.
PS: If you need to use a parametrized query in a data macro it looks like the best bet is with the AfterInsert event or AfterUpdate event as they can support parameters.
I have job in Talend that is designed to bring together some data from different databases: one is a MySQL database and the other a MSSQL database.
What I want to do is match a selection of loan numbers from the MySQL database (about 82,000 loan numbers) to the corresponding information we have housed in the MSSQL database.
However, the tables in MSSQL to which I am joining the data from MySQL are much larger (~ 2 million rows), are quite wide, and thus cost much more time to query. Ideally I could perform an inner join between the two tables based on the loan number, but since they are in different databases this is not possible. The inner join that is performed inside a tMap occurs after the Lookup input has already returned its data set, which is quite large (especially since this particular MSSQL query will execute a user-defined function for each loan number).
Is there any way to create a global variable out of the output from the MySQL query (namely, the loan numbers selected by the MySQL query) and use that global variable as an IN clause in the MSSQL query?
This should be possible. I'm not working in MySQL but I have something roughly equivalent here that I think you should be able to adapt to your needs.
I've never actually answered a Stackoverflow question and while I was typing this the page started telling me I need at least 10 reputation to post more than 2 pictures/links here and I think I need 4 pics, so I'm just going to write it out in words here and post the whole thing complete with illustrations on my blog in case you need more info (quite likely, I should think!)
As you can see, I've got some data coming out of the table and getting filtered by tFilterRow_1 to only show the rows I'm interested in.
The next step is to limit it to just the field I want to use in the variable. I've used tMap_3 rather than a tFilterColumns because the field I'm using is a string and I wanted to be able to concatenate single quotes around it but if you're using an integer you might not need to do that. And of course if you have a lot of repetition you might also want to get a tUniqueRows in there as well to save a lot of unnecessary repetition
The next step is the one that does the magic. I've got a list like this:
'A1'
'A2'
'B1'
'B2'
etc, and I want to turn it into 'A1','A2','B1','B2' so I can slot it into my where clause. For this, I've used tAggregateRow_1, selecting "list" as the aggregate function to use.
Next up, we want to take this list and put it into a context variable (I've already created the context variable in the metadata - you know how to do that, right?). Use another tMap component, feeding into a tContextLoad widget. tContextLoad always has two columns in its schema, so map the output of the tAggregateRows to the "value" column and enter the name of the variable in the "key". In this example, my context variable is called MyList
Now your list is loaded as a text string and stored in the context variable ready for retrieval. So open up a new input and embed the variable in the sql code like this
"SELECT distinct MY_COLUMN
from MY_SECOND_TABLE where the_selected_row in ("+
context.MyList+")"
It should be as easy as that, and when I whipped it up it worked first time, but let me know if you have any trouble and I'll see what I can do.
I have a query in a base-data table that (given that my search criteria are correct) gives back approx. 950 records.
Except of the 3 criteria fields, i want to have about 10 more fields (the Project is still at the beginning) , every single one based on sub-queries, some of them normal select queries, some are aggregated queries.
As far as i know every sub-query must give 1 and only one value back.
This value school be individual for every Record of the top query.
My Problem now is, that i don't know how to pass the search criteria from the top query (simple select query) to the sub-query in the in 10 fields i mentioned before.
Is this possible at all, or is my Approach to complicated. Is there possibly an easier way?
I have a Windows 7 System with Office 2010 installed.
Your help is much appreciated.
Thanks a lot.
PS
The sub-queries are based on the same table as the top query. Sorry, I forgot to mention.
You can pass arguments between things with a function call to set a public variable. This vba must be in a Module, not behind a Form Module. I don't use this approach very often, because the global value is in volatile memory, I prefer to save the variable in a special data Table.
Public strGlobal As String
Function Func_ReadGlobal() As String
Func_ReadGlobal = strGlobal
End Function
Function Func_WriteGlobal() As String
strGlobal = Func_WriteGlobal
End Function
In all subqueries create parameter(s) and use it as search criteria. Parameter name should be the same for same column. Now, if you use those subqueries in your main query, Access will ask only once per each parameter name, you don't need to pass them explicitly to subqueries.
Thank you guys.
I did'nt think of the most obvious solution with the Globals. I will try it out as soon as my Boss gives me the time to continue with the Project.
#Sergey
I can't use the Parameter(s) way, because the whole query, incl. Subqueries shall run completely alone in VBA, without human input at all.
I have an online database CUSTOMERINFO with more than 100k details stored like following format Cust Id, Customer name, Addr, Phone,.......,Call back time
I want to retrieve data when call back time equals current time automatically.
I have designed front end with Java and currently 10 employees working with the database and now they are manually retrieving the data by ID,..
I know select command is very useful to retrieve but I want it to do automatically instead of calling each time manually.
Edited:
When the customer data is retrieved from table, either we will set another call back time or no call back and then pushed into table again.. In the next time if no call back is set in the place of call back time that row no need to be retrieved.
I'm likely missing something here, but:
Something like SELECT ... FROM table WHERE 'Call back time' >= NOW()
I'd recommend not using simply equals, as has been said in the comments, because you might miss items.
If you update the callback time after you have retrieved the callback items, that should work as long as you do not do the query to get callbacks more than once every few seconds.
As was mentioned in the comments, this is just the start though. There are going to be other issues you'll have to deal with.
This may be a stupid question but is it possible to store a count query in a field in a table such that when the result of the count changes the result will update itself?
Thread(ThreadID,NumMessages)
Message(MessageID,ThreadID,MessageText,PreviousMessage)
I want to update the Thread.NumMessages field any time a message with the corresponding ThreadID gets added or removed. I know I can do this by incrementing/decrementing the Thread.NumMessages field of by using a count query
SELECT COUNT(*), FROM SCHEMA.Message WHERE ThreadID='SOMETHREADID'
But is there anyway of setting up the NumMessages field so this is kept up to date without it being done explicitly at every addition and delete?
Thanks
Graeme
yes, you can use a view as the implementation of your Thread table.
http://dev.mysql.com/doc/refman/5.1/en/create-view.html
Create view thread_view
select
count(*) as NumMessages,
threadID
from message
group by threadID
Triggers!
You're wanting a trigger. This should help you with your searching (knowing what to look for is half the battle). http://www.databasedesign-resource.com/mysql-triggers.html
Basically, a trigger fires any time a designated event (such as insert) on a table is tripped, and executes a stored procedure.
your stored procedure would then check to make sure it's something it cares about (you can add all sorts of logic here), then does something (increment that value?) before MySQL executes the original query that triggered it in the first place.
http://www.roseindia.net/mysql/mysql5/triggers.shtml