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Ternary and coalesce operators in Azure Cosmos DB for NoSQL

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APPLIES TO: NoSQL

Ternary and coalesce operators in Azure Cosmos DB for NoSQL evaluates expressions and returns a result depending on a boolean operand or if a field exists. Both the ternary and coalesce operators function similarly to popular programming languages like C# and JavaScript. Use the ternary (?) and coalesce (??) operators to build conditional expressions that are resilient against semi-structured or mixed-type data.

Ternary operator

The ? operator returns a value depending on the evaluation of the first expression.

Syntax

<bool_expr> ?  
    <expr_true> : 
    <expr_false>

Arguments

Description
bool_expr A boolean expression.
expr_true The expression to evaluate if bool_expr evaluates to true.
expr_false The expression to evaluate if bool_expr evaluates to false.

Examples

Consider these items in a container. They contain multiple metadata properties related to pricing, and one of the properties doesn't exist on all items.

[
  {
    "name": "Stangincy trekking poles",
    "price": 24.50,
    "onCloseout": false,
    "onSale": true,
    "collapsible": true
  },
  {
    "name": "Vimero hiking poles",
    "price": 24.50,
    "onCloseout": false,
    "onSale": false
  },
  {
    "name": "Kramundsen trekking poles",
    "price": 24.50,
    "onCloseout": true,
    "onSale": true,
    "collapsible": false
  }
]

This query evaluates the expression onSale, which is equivalent to onSale = true. The query then returns the price multiplied by 0.85 if true or the price unchanged if false.

SELECT
    p.name,
    p.price AS subtotal,
    p.onSale ? (p.price * 0.85) : p.price AS total
FROM
    products p

[
  {
    "name": "Stangincy trekking poles",
    "subtotal": 24.5,
    "total": 20.825
  },
  {
    "name": "Vimero hiking poles",
    "subtotal": 24.5,
    "total": 24.5
  },
  {
    "name": "Kramundsen trekking poles",
    "subtotal": 24.5,
    "total": 20.825
  }
]

You can also nest calls to the ? operator. This example adds an extra calculation based on a second property (taxFree)

SELECT
    p.name,
    p.price AS subtotal,
    p.onCloseout ? (p.price * 0.55) : p.onSale ? (p.price * 0.85) : p.price AS total
FROM
    products p

[
  {
    "name": "Stangincy trekking poles",
    "subtotal": 24.5,
    "total": 20.825
  },
  {
    "name": "Vimero hiking poles",
    "subtotal": 24.5,
    "total": 24.5
  },
  {
    "name": "Kramundsen trekking poles",
    "subtotal": 24.5,
    "total": 13.475000000000001
  }
]

As with other query operators, the ? operator excludes items if the referenced properties are missing or the types being compared are different.

Coalesce operator

Use the ?? operator to efficiently check for a property in an item when querying against semi-structured or mixed-type data.

For example, this query assumes that any item where the property collapsible isn't present, isn't collapsible.

SELECT
    p.name,
    p.collapsible ?? false AS isCollapsible
FROM
    products p

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