MongoDB query equivalent in SQL

[David_King]

I am relatively new to MongoDb as well as RDBMS.

I understand that, in SQL, even though I don’t have data for the field, the field will be available. Whereas in MongoDB if the data is not there, the field won’t be there.

Out of curiosity, is there a SQL Query Equivalent to the below MongoDb query?

db.goods.find({“product” :{ $exists : true }});

[Stennie]

Welcome to the community @David_King!

@David_King

Out of curiosity, is there a SQL Query Equivalent to the below MongoDb query?

In SQL a field will always exist, but the value may be nullable. The closest equivalent to an $exists query would be:

SELECT * FROM goods where product IS NOT NULL

For a general guide to roughly equivalent SQL queries, the MongoDB manual has some helpful reference pages:

• SQL to MongoDB Mapping Chart
• SQL to Aggregation Mapping Chart

Typically you will not use identical data models in MongoDB vs RDBMS. I included more on this in a discussion yesterday, so please read my related post for more details:

@Stennie

This is a great use case for MongoDB, but I would encourage you to think about how your data model might be adjusted to take advantage of MongoDB’s indexing and flexible schema rather than doing a direct 1:1 translation of an existing SQL schema. You could start with a direct translation, but this typically misses out on some benefits like easier querying and better performance.

Regards,
Stennie

[David_King]

@Stennie, thanks for the explanation.