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Comparison Semantics

Performing any of the following Entity SQL operators involves comparison of type instances:

Explicit comparison

Equality operations:

  • =

  • !=

Ordering operations:

  • <

  • <=

  • >

  • >=

Nullability operations:

  • IS NULL

  • IS NOT NULL

Explicit distinction

Equality distinction:

  • DISTINCT

  • GROUP BY

Ordering distinction:

  • ORDER BY

Implicit distinction

Set operations and predicates (equality):

  • UNION

  • INTERSECT

  • EXCEPT

  • SET

  • OVERLAPS

Item predicates (equality):

  • IN

Supported Combinations

The following table shows all the supported combinations of comparison operators for each kind of type:

 

Type

=

!=

GROUP BY

DISTINCT

UNION

INTERSECT

EXCEPT

SET

OVERLAPS

IN

< <=

> >=

ORDER BY

IS NULL

IS NOT NULL

Entity type

Ref1

All properties2

All properties2

All properties2

Throw3

Throw3

Ref1

Complex type

Throw3

Throw3

Throw3

Throw3

Throw3

Throw3

Throw3

Row

All properties4

All properties4

All properties4

Throw3

Throw3

All properties4

Throw3

Primitive type

Provider-specific

Provider-specific

Provider-specific

Provider-specific

Provider-specific

Provider-specific

Provider-specific

Multiset

Throw3

Throw3

Throw3

Throw3

Throw3

Throw3

Throw3

Ref

Yes5

Yes5

Yes5

Yes5

Throw

Throw

Yes5

Association

type

Throw3

Throw

Throw

Throw

Throw3

Throw3

Throw3

1The references of the given entity type instances are implicitly compared, as shown in the following example:

SELECT p1, p2 
FROM AdventureWorksEntities.Product AS p1 
     JOIN AdventureWorksEntities.Product AS p2 
WHERE p1 != p2 OR p1 IS NULL

An entity instance cannot be compared to an explicit reference. If this is attempted, an exception is thrown. For example, the following query will throw an exception:

SELECT p1, p2 
FROM AdventureWorksEntities.Product AS p1 
     JOIN AdventureWorksEntities.Product AS p2 
WHERE p1 != REF(p2)

2Properties of complex types are flattened out before being sent to the store, so they become comparable (as long as all their properties are comparable). Also see 4.

3The Entity Framework runtime detects the unsupported case and throws a meaningful exception without engaging the provider/store.

4An attempt is made to compare all properties. If there is a property that is of a non-comparable type, such as text, ntext, or image, a server exception might be thrown.

5All individual elements of the references are compared (this includes the entity set name and all the key properties of the entity type).

See Also




Build Date:

2012-10-01
Show:
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