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Scalar expressions in Azure Cosmos DB for NoSQL

  • Artikkeli

APPLIES TO: NoSQL

The SELECT clause supports scalar expressions. A scalar expression is a combination of symbols and operators that can be evaluated to obtain a single value. Examples of scalar expressions include: constants, property references, array element references, alias references, or function calls. Scalar expressions can be combined into complex expressions using operators.

Syntax

<scalar_expression> ::=  
       <constant>
     | input_alias
     | parameter_name  
     | <scalar_expression>.property_name  
     | <scalar_expression>'['"property_name"|array_index']'  
     | unary_operator <scalar_expression>  
     | <scalar_expression> binary_operator <scalar_expression>    
     | <scalar_expression> ? <scalar_expression> : <scalar_expression>  
     | <scalar_function_expression>  
     | <create_object_expression>
     | <create_array_expression>  
     | (<scalar_expression>)
  
<scalar_function_expression> ::=  
        'udf.' Udf_scalar_function([<scalar_expression>][,…n])  
        | builtin_scalar_function([<scalar_expression>][,…n])  
  
<create_object_expression> ::=  
   '{' [{property_name | "property_name"} : <scalar_expression>][,…n] '}'  
  
<create_array_expression> ::=  
   '[' [<scalar_expression>][,…n] ']'

Arguments

Description
<constant> Represents a constant value. See Constants section for details.
input_alias Represents a value defined by the input_alias introduced in the FROM clause.
This value is guaranteed to not be undefined –undefined values in the input are skipped.
<scalar_expression>.property_name Represents a value of the property of an object. If the property doesn't exist or property is referenced on a value, which isn't an object, then the expression evaluates to undefined value.
<scalar_expression>'['"property_name"|array_index']' Represents a value of the property with name property_name or array element with index array_index of an array. If the property/array index doesn't exist or the property/array index is referenced on a value that isn't an object/array, then the expression evaluates to undefined value.
unary_operator <scalar_expression> Represents an operator that is applied to a single value.
<scalar_expression> binary_operator <scalar_expression> Represents an operator that is applied to two values.
<scalar_function_expression> Represents a value defined by a result of a function call.
udf_scalar_function Name of the user-defined scalar function.
builtin_scalar_function Name of the built-in scalar function.
<create_object_expression> Represents a value obtained by creating a new object with specified properties and their values.
<create_array_expression> Represents a value obtained by creating a new array with specified values as elements
parameter_name Represents a value of the specified parameter name. Parameter names must have a single @ as the first character.

Examples

The most common example of a scalar expression is a math equation.

SELECT VALUE
    ((2 + 11 % 7) - 2) / 2

[
  2
]

In this next example, the result of the scalar expression is a boolean:

SELECT
    ("Redmond" = "WA") AS isCitySameAsState,
    ("WA" = "WA") AS isStateSameAsState

[
  {
    "isCitySameAsState": false,
    "isStateSameAsState": true
  }
]

Remarks

  • All arguments must be defined when calling a built-in or user-defined scalar function. If any of the arguments is undefined, the function isn't called, and the result is undefined.
  • Any property that is assigned undefined value is skipped and not included in the created object when creating an object.
  • Any element value that is assigned undefined value is skipped and not included in the created object when creating an array. This skip causes the next defined element to take its place in such a way that the created array doesn't skip indexes.

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