Combining comparison operators in MongoDB - Step-by-Step Execution

Concept Flow - Combining comparison operators

Start Query

↓

Specify Field

↓

Apply Comparison Operators

↓

Combine with $and / $or

↓

Execute Query

↓

Return Matching Documents

The query starts by specifying a field, applies comparison operators, combines them with logical operators like $and or $or, then executes to return matching documents.

Execution Sample

MongoDB

db.products.find({
  $and: [
    { price: { $gt: 10 } },
    { price: { $lt: 50 } }
  ]
})

This query finds products with price greater than 10 and less than 50.

Execution Table

Step	Query Part	Evaluation	Matching Documents
1	Start Query	Begin with empty filter	All documents
2	Apply { price: { $gt: 10 } }	Filter documents where price > 10	Docs with price > 10
3	Apply { price: { $lt: 50 } }	Filter documents where price < 50	Docs with price < 50
4	Combine with $and	Documents must satisfy both conditions	Docs with 10 < price < 50
5	Execute Query	Return filtered documents	Docs with price between 10 and 50
6	End	No more steps	Query complete

💡 Query ends after applying all conditions combined with $and

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Matching Documents	All documents	Docs with price > 10	Docs with price < 50	Docs with price > 10 and price < 50	Docs with price between 10 and 50

Key Moments - 2 Insights

Why do we need to use $and to combine multiple comparison operators on the same field?

Because MongoDB requires combining multiple conditions on the same field using $and; writing { price: { $gt: 10, $lt: 50 } } works too, but $and explicitly shows combining separate conditions. See execution_table rows 3 and 4.

Can we combine comparison operators without $and or $or?

Yes, if they are on the same field, you can combine them inside one object like { price: { $gt: 10, $lt: 50 } }. Using $and is necessary when combining conditions on different fields or complex logic. See execution_table row 4.

Visual Quiz - 3 Questions

Look at the execution table, what documents remain after Step 3?

A Documents with price less than 50

B Documents with price greater than 10

C Documents with price greater than 10 and less than 50

D All documents

💡 Hint

Check the 'Matching Documents' column at Step 3 in the execution_table

At which step does the query combine conditions to require both to be true?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look for the step mentioning $and in the 'Query Part' column of execution_table

If we remove the $and and write { price: { $gt: 10, $lt: 50 } }, how does the variable 'Matching Documents' after Step 4 change?

A It includes documents with price less than 10

B It remains the same, documents with price between 10 and 50

C It includes documents with price greater than 50

D It becomes empty

💡 Hint

Refer to variable_tracker showing final matching documents for combined conditions on the same field

Concept Snapshot

MongoDB combines comparison operators using $and or $or.
Example: {$and: [{price: {$gt: 10}}, {price: {$lt: 50}}]}.
Alternatively, combine on same field: {price: {$gt: 10, $lt: 50}}.
Query returns documents matching all combined conditions.
Use $and for multiple fields or complex logic.

Full Transcript

This visual execution shows how MongoDB combines comparison operators to filter documents. The query starts empty, then applies price > 10, then price < 50, and combines these with $and to require both conditions. The matching documents narrow down step by step until only those with price between 10 and 50 remain. Key points include how $and combines conditions and that multiple operators on the same field can be combined inside one object. The execution table and variable tracker clearly show the filtering process and final results.