Let’s break down exactly what’s happening here and how to fix it:

The root of the confusion #

Your current query {"NUM": {$gte: 25, $lte:25}} isn’t checking for an element exactly equal to 25 in the array. MongoDB interprets this range condition differently for array fields:

Does the NUM array contain at least one element that is >=25 AND at least one element that is <=25?

For the document with _id:3, the array [24,26,28] meets both criteria:

• 26 is >=25
• 24 is <=25

Even though no single element is exactly 25, the combination of these two elements satisfies the query’s conditions—so the document gets returned.

The fix for exact matching #

When your from and to parameters are identical (and you want to find arrays that contain that exact value), use a direct equality match instead of range operators:

db.runCommand( { 
  aggregate: "mycoll", 
  pipeline: [ 
    { "$match": {"NUM": 25 } } 
  ] 
} )

This query will only return documents where the NUM array includes the exact value 25. For your sample data, this correctly returns only the document with _id:2.

Bonus: Ensuring a single element meets both range conditions #

If you ever need to verify that one element in the array satisfies all range conditions (not separate elements), use the $elemMatch operator. While it’s unnecessary for exact matches, it’s useful for more complex range checks:

db.runCommand( { 
  aggregate: "mycoll", 
  pipeline: [ 
    { "$match": {"NUM": { $elemMatch: { $gte:25, $lte:25 } } } } 
  ] 
} )

$elemMatch forces MongoDB to check that a single element in the array meets all specified conditions—here, that means an element equal to 25.

内容的提问来源于stack exchange，提问作者Kamlesh Kanazariya