MongoDB $cmp Operator (original) (raw)

Last Updated : 5 May, 2026

The MongoDB $cmp operator compares two values and returns their order. It is used in aggregation pipelines for sorting and conditional logic, and follows BSON type ordering for different data types.

• Compares two expressions and returns their relative order.
• Outputs 0, 1, or -1 based on the comparison result.
• Useful for building comparison-based expressions within aggregation pipelines.
• Helps implement conditional logic in pipelines.
• Works across different data types using BSON ordering.

Syntax

{ $cmp: [ , ] }

• ****:** The first value or field to compare.
• ****:** The second value or field to compare.

Features of the MongoDB $cmp Operator

Here are some features discussed:

• Returns -1 if the first value is smaller, 1 if greater, and 0 if equal.
• Supports comparisons on nested (embedded) fields.
• Considers both value and data type during comparison.
• Follows BSON type ordering when comparing different data types.
• Used within aggregation pipeline stages like project,project, project,sort, and conditional expressions.

MongoDB $cmp Operator Examples

Examples of the $cmp operator in MongoDB. In the following examples, we are working with:

• **Database: GeeksforGeeks
• **Collection: example
• **Document: Two documents that contain the details of the shapes in the form of field-value pairs.

Example 1: Using $cmp to Compare a Field with a Static Value

The $cmp operator compares the value of the side field with 4 and returns 0, which indicates that both values are equal.

**Query:

db.example.aggregate([{$match: {name: "Square"}}, {$project: {result: {$cmp:["$side", 4]}}}])

**Output:

Example 2: Using $cmp Operator in the embedded Document

Comparing the value of the measurement.height field with the value of the measurement.width field and $cmp operator return -1 which means both values of measurement.height field is less than the value of the measurement.width field.

**Query:

db.example.aggregate([{$match: {name: "Rectangle"}}, {$project: {result: {$cmp:["$measurement.height", "$measurement.width"]}}}])

**Output: