关系数据库结构设计建议

Question

This is a textual description of data for which I need to create a database design (using SQLite) for an application.

The application needs to keep a record of operations . Each operation has a Name and its list of parameters. Each parameter has its Name and a Value. However, the values of the parameters will change over the lifetime of the app (in fact the user will be able to changes them using GUI) and we want to keep a history of the values which a certain parameter has had. Furthermore, each operation can have multiple parameter sets . A parameter set is like an envelope which encompasses a set of parameter values (which all belong to the same operation) and gives this envelope a unique Number and a non-unique Description .

This is what I have so-far: [Database model image][1]

The database model should allow me to perform these actions on the database data:

1. Show a list of operations - I know how to do this.
2. Show a list of parameters for a given operation - I know how to do this.
3. For a given operation, show all its parameters as columns and show the values of the parameters as rows - each row represents a different parameter value from the history of values. I'm stuck at this one.
4. For a given operation, show a list of all parameter sets which belong to that operation. I'm stuck at this one too.
5. For a given operation and for a given parameter set, get the latest values of its parameters. Stuck at this.

I'm not sure if I should re-work my database model or if I should look for proper SQL statements to accomplish the tasks above with the model that I have. Any help is greatly appreciated. Thank you.

EDIT 1

I have re-worked my database model according to a helpful advice from @Marek Herman. Thanks to that I am able to accomplish tasks 1) 2) 4). Now I'm trying to accomplish 5) which should not be that difficult with the current database model. I have this SQL statement:

SELECT Parameter.ParameterIdentifier, ParameterValue.ParameterValue,
ParameterValueVersion.VersionNumber, ParameterValueVersion.ChangedOn
FROM ParameterValueVersion INNER JOIN
(((Operation INNER JOIN Parameter ON Operation.OperationPLC_ID = Parameter.OperationPLC_ID)
INNER JOIN ParameterSet ON Operation.OperationPLC_ID = ParameterSet.OperationPLC_ID)
INNER JOIN ParameterValue ON (ParameterSet.ID = ParameterValue.ParameterSetID) AND
(Parameter.ID = ParameterValue.ParameterID)) ON ParameterValueVersion.ID = ParameterValue.ParameterValueVersionID
WHERE (Operation.OperationPLC_ID=[opID] AND 
ParameterSet.ParameterSetNumber=[parSetNum]);

where [opID] and [parSetNum] are the input parameters. This SQL statement actually only joins all these tables together on their PK->FK relationship: Operation, Parameter, ParameterSet, ParameterValue, ParameterValueVersion and filters the rows by specified OperationPLC_ID and ParameterSetNumber.

Here is an example of an output of this SQL statement. Each row shows a name of a parameter, its value, a version number of the value and date of change of that value. Some parameters only have one value (only one version -eg, "OFFSET"). Some parameters have two values. For example "PREFILLING" has a value of "3" which was input on Oct 20, 2016 (and has a version number 1) and it also has a value of "3.5" which was input on Oct 21, 2016 and has a version number of 2. So I'd like to show only the latest versions of the values of the parameters. Any advice how to modify the SQL statement is much appreciated. Thank you.

EDIT 2

I guess I figured out how to perform 5). I had to study a bit how GROUP BY works. This did the trick:

SELECT Parameter.ParameterIdentifier, last(ParameterValue.ParameterValue) AS ParameterValue, last(ParameterValueVersion.ChangedOn) AS ChangedOn, max(ParameterValueVersion.VersionNumber) AS VersionNumber
FROM ParameterValueVersion INNER JOIN
(((Operation INNER JOIN Parameter ON Operation.OperationPLC_ID = Parameter.OperationPLC_ID)
INNER JOIN ParameterSet ON Operation.OperationPLC_ID = ParameterSet.OperationPLC_ID)
INNER JOIN ParameterValue ON (ParameterSet.ID = ParameterValue.ParameterSetID) AND
(Parameter.ID = ParameterValue.ParameterID)) ON ParameterValueVersion.ID = ParameterValue.ParameterValueVersionID
WHERE (((Operation.OperationPLC_ID)=[opID]) AND ((ParameterSet.ParameterSetNumber)=[parSetNum]))
GROUP BY Parameter.ParameterIdentifier
ORDER BY Parameter.ParameterIdentifier

Now I still need to figure out how to perform task no. 3. I'm gonna study the suggested COALESCE function. Thank you.

Answer 1

0) I would connect ParameterSet to Operation and Parameter and not to ParameterValue.

• 1) okay!
• 2) okay!
• 3) I think you can use the COALESCE() function to display the columns and then it should be possible to show all parameters with matching OperationID
• 4) you can do that if you do point #0
• 5) same as above I think