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Add reference Markdown: operators/conditional-expression #47

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269 changes: 269 additions & 0 deletions reference/operators/conditional-expression/$cond.md
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---
title: $cond
description: The $cond operator is used to evaluate a condition and return one of two expressions based on the result.
type: operators
category: conditional-expression
---

# $cond

The `$cond` operator is used to evaluate a condition and return one of two expressions based on the result. It's similar to the ternary operator in many programming languages. The `$cond` operator can be used within aggregation pipelines to add conditional logic to your queries.

## Syntax

```javascript
{
$cond: {
if: <boolean-expression>,
then: <true-case>,
else: <false-case>
}
}
```

### Parameters

| Parameter | Description |
| --- | --- |
| **if**| A boolean expression that is evaluated.|
| **then**| The expression to return if the `if` condition evaluates to true.|
| **else**| The expression to return if the `if` condition evaluates to false.|

## Examples

Consider this sample document from the stores collection.

```json
{
"_id": "0fcc0bf0-ed18-4ab8-b558-9848e18058f4",
"name": "First Up Consultants | Beverage Shop - Satterfieldmouth",
"location": {
"lat": -89.2384,
"lon": -46.4012
},
"staff": {
"totalStaff": {
"fullTime": 8,
"partTime": 20
}
},
"sales": {
"totalSales": 75670,
"salesByCategory": [
{
"categoryName": "Wine Accessories",
"totalSales": 34440
},
{
"categoryName": "Bitters",
"totalSales": 39496
},
{
"categoryName": "Rum",
"totalSales": 1734
}
]
},
"promotionEvents": [
{
"eventName": "Unbeatable Bargain Bash",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 6,
"Day": 23
},
"endDate": {
"Year": 2024,
"Month": 7,
"Day": 2
}
},
"discounts": [
{
"categoryName": "Whiskey",
"discountPercentage": 7
},
{
"categoryName": "Bitters",
"discountPercentage": 15
},
{
"categoryName": "Brandy",
"discountPercentage": 8
},
{
"categoryName": "Sports Drinks",
"discountPercentage": 22
},
{
"categoryName": "Vodka",
"discountPercentage": 19
}
]
},
{
"eventName": "Steal of a Deal Days",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 9,
"Day": 21
},
"endDate": {
"Year": 2024,
"Month": 9,
"Day": 29
}
},
"discounts": [
{
"categoryName": "Organic Wine",
"discountPercentage": 19
},
{
"categoryName": "White Wine",
"discountPercentage": 20
},
{
"categoryName": "Sparkling Wine",
"discountPercentage": 19
},
{
"categoryName": "Whiskey",
"discountPercentage": 17
},
{
"categoryName": "Vodka",
"discountPercentage": 23
}
]
}
]
}
```

### Example 1: Determine high sales categories

This query determines if the sales for each category are considered "high" or "low" based on a threshold value of $250,000.

```javascript
db.stores.aggregate([{
$project: {
_id: 0,
storeId: "$storeId",
category: "$sales.salesByCategory.categoryName",
sales: "$sales.salesByCategory.totalSales",
salesCategory: {
$cond: {
if: {
$gte: ["$sales.salesByCategory.totalSales", 250000]
},
then: "High",
else: "Low"
}
}
}
},
// Limit the result to the first 3 documents
{
$limit: 3
}
])
```

The first three results returned by this query are:

```json
[
{
"sales": [
35921,
1000
],
"category": [
"DJ Headphones",
"DJ Cables"
],
"salesCategory": "High"
},
{
"sales": [
4760
],
"category": [
"Guitars"
],
"salesCategory": "High"
},
{
"sales": [
14697,
44111,
37854,
46211,
7269,
25451,
21083
],
"category": [
"Washcloths",
"Innerspring Mattresses",
"Microfiber Towels",
"Shower Curtains",
"Bathrobes",
"Tablecloths",
"Bath Accessories"
],
"salesCategory": "High"
}
]
```

### Example 2: Determine full-time or part-time dominance

This query determines whether a store employs more full-time or part-time staff.

```javascript
db.stores.aggregate([{
$project: {
name: 1,
staffType: {
$cond: {
if: {
$gte: ["$staff.totalStaff.fullTime", "$staff.totalStaff.partTime"]
},
then: "More Full-Time",
else: "More Part-Time"
}
}
}
},
// Limit the result to the first 3 documents
{
$limit: 3
}
])
```

The first three results returned by this query are:

```json
[
{
"_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
"name": "Lakeshore Retail | DJ Equipment Stop - Port Cecile",
"staffType": "More Full-Time"
},
{
"_id": "649626c9-eda1-46c0-a27f-dcee19d97f41",
"name": "VanArsdel, Ltd. | Musical Instrument Outlet - East Cassie",
"staffType": "More Full-Time"
},
{
"_id": "8345de34-73ec-4a99-9cb6-a81f7b145c34",
"name": "Northwind Traders | Bed and Bath Place - West Oraland",
"staffType": "More Part-Time"
}
]
```
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