c# - How to make relation between tables which are in same dataset? - Stack Overflow
The following example uses the ChildRelations property to return each child DataRelation in a DataTable. Each relation is then used as an argument in the. If you're creating a typed dataset, it's easiest to create the relations in Visual Studio's For example, instead of having one DataTable for Product Category and. This dialog is used to manage relations between both new and previously added data tables in your analysis. When data tables have been related, they can be.
Base and derived relations[ edit ] Main articles: Relvar and View database In a relational database, all data are stored and accessed via relations. Relations that store data are called "base relations", and in implementations are called "tables". Other relations do not store data, but are computed by applying relational operations to other relations. These relations are sometimes called "derived relations". In implementations these are called " views " or "queries". Derived relations are convenient in that they act as a single relation, even though they may grab information from several relations.
Also, derived relations can be used as an abstraction layer. Mathematically, attaching a domain to an attribute means that any value for the attribute must be an element of the specified set.
Details on Manage Relations
The character string "ABC", for instance, is not in the integer domain, but the integer value is. Another example of domain describes the possible values for the field "CoinFace" as "Heads","Tails". So, the field "CoinFace" will not accept input values like 0,1 or H,T.
Constraints[ edit ] Constraints make it possible to further restrict the domain of an attribute. For instance, a constraint can restrict a given integer attribute to values between 1 and Constraints provide one method of implementing business rules in the database and support subsequent data use within the application layer.
SQL implements constraint functionality in the form of check constraints. Constraints restrict the data that can be stored in relations. These are usually defined using expressions that result in a boolean value, indicating whether or not the data satisfies the constraint. Constraints can apply to single attributes, to a tuple restricting combinations of attributes or to an entire relation.
Relational database - Wikipedia
Since every attribute has an associated domain, there are constraints domain constraints. The two principal rules for the relational model are known as entity integrity and referential integrity.
Unique key A primary key uniquely specifies a tuple within a table. In order for an attribute to be a good primary key it must not repeat.
While natural attributes attributes used to describe the data being entered are sometimes good primary keys, surrogate keys are often used instead. A surrogate key is an artificial attribute assigned to an object which uniquely identifies it for instance, in a table of information about students at a school they might all be assigned a student ID in order to differentiate them.
The surrogate key has no intrinsic inherent meaning, but rather is useful through its ability to uniquely identify a tuple. Another common occurrence, especially in regard to N: M cardinality is the composite key. A composite key is a key made up of two or more attributes within a table that together uniquely identify a record.
For example, in a database relating students, teachers, and classes. Classes could be uniquely identified by a composite key of their room number and time slot, since no other class could have exactly the same combination of attributes. In fact, use of a composite key such as this can be a form of data verificationalbeit a weak one.
Foreign key A foreign key is a field in a relational table that matches the primary key column of another table. The foreign key can be used to cross-reference tables.
Eager Loading Relationships - Laravel DataTables YajraBox
Foreign keys do not need to have unique values in the referencing relation. Foreign keys effectively use the values of attributes in the referenced relation to restrict the domain of one or more attributes in the referencing relation. A foreign key could be described formally as: Stored procedure A stored procedure is executable code that is associated with, and generally stored in, the database. Stored procedures usually collect and customize common operations, like inserting a tuple into a relationgathering statistical information about usage patterns, or encapsulating complex business logic and calculations.
Frequently they are used as an application programming interface API for security or simplicity. Stored procedures are not part of the relational database model, but all commercial implementations include them.
If the active relationship is between DateKey and OrderDate, that is the default relationship in formulas unless you specify otherwise. A relationship can be created when the following requirements are met: Criteria Description Unique Identifier for Each Table Each table must have a single column that uniquely identifies each row in that table.
Using Data Relation with Data Table
This column is often referred to as the primary key. Unique Lookup Columns The data values in the lookup column must be unique. In a Data Model, nulls and empty strings are equivalent to a blank, which is a distinct data value. Compatible Data Types The data types in the source column and lookup column must be compatible.
For more information about data types, see Data types supported in Data Models. In a Data Model, you cannot create a table relationship if the key is a composite key. Other relationship types are not supported.
You can do this before you import the data, or by creating a calculated column in the Data Model using the Power Pivot add-in. However, you can use DAX functions to model many-to-many relationships. A self-join is a recursive relationship between a table and itself. Self-joins are often used to define parent-child hierarchies. In other words, the following set of relationships is prohibited. Automatic detection and inference of relationships in Power Pivot One of the advantages to importing data using the Power Pivot add-in is that Power Pivot can sometimes detect relationships and create new relationships in the Data Model it creates in Excel.
When you import multiple tables, Power Pivot automatically detects any existing relationships among the tables. The detection algorithm uses statistical data about the values and metadata of columns to make inferences about the probability of relationships.
Data types in all related columns should be compatible. For automatic detection, only whole number and text data types are supported.
For the relationship to be successfully detected, the number of unique keys in the lookup column must be greater than the values in the table on the many side. In other words, the key column on the many side of the relationship must not contain any values that are not in the key column of the lookup table. For example, suppose you have a table that lists products with their IDs the lookup table and a sales table that lists sales for each product the many side of the relationship.
To have Excel detect the relationship, you need to first update the Product lookup table with the IDs of the missing products.