In MongoDB the db.collection.update() method modifies an existing document or documents in a collection.
By default, it only updates a single document. But if multi: true is specified, then it updates all documents that match the query criteria.
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MongoDB updateOne()
In MongoDB the db.collection.updateOne() method updates a single document within the collection based on the filter.
MongoDB insert()
In MongoDB the db.collection.insert() method inserts a document or documents into a collection.
The collection part is the name of the collection to insert the document/s into.
MongoDB insertMany()
In MongoDB the db.collection.insertMany() method inserts multiple documents into a collection.
The collection part is the name of the collection to insert the documents into.
MongoDB insertOne()
In MongoDB the db.collection.insertOne() method inserts a single document into a collection.
The collection part is the name of the collection to insert the document into.
MongoDB Upsert Explained
Many update operations in MongoDB have the potential to be upserts. An upsert is a combination of an insert and an update.
It works like this: You perform an update operation based on filter criteria, and if there are any matches, only the matched documents are updated, but if there are no matches, then a new document is inserted.
Continue readingSQL ALTER TABLE for Beginners
In SQL, the ALTER TABLE statement modifies the definition of an existing table.
You can use ALTER TABLE to alter, add, or drop columns and constraints.
Depending on your DBMS, the ALTER TABLE statement can also be used to reassign and rebuild partitions, or disable and enable constraints and triggers.
SQL UNION Clause for Beginners
In SQL, the UNION clause concatenates the results of two queries into a single result set.
You can use the UNION clause with or without the ALL argument:
UNION ALL– Includes duplicates.UNION– Excludes duplicates.
Some RDBMSs also accept UNION DISTINCT, which is the equivalent to UNION. That is, it excludes duplicates.
Below are some basic examples to demonstrate how it works.
Continue readingSQL AVG() for Beginners
In SQL, the AVG() function is an aggregate function that returns the average of all values in a given expression.
It can also be used to return the average of all distinct (unique) values in an expression.
The expression must be numeric (it cannot be character string, bit string, or datetime).
Below are some basic examples to demonstrate how it works.
Continue readingSQL SUM() for Beginners
In SQL, the SUM() function is an aggregate function that returns the sum of all values in a given expression.
It can also be used to return the sum of all distinct (unique) values in an expression.
The expression must be numeric (it cannot be character string, bit string, or datetime).
Below are some basic examples to demonstrate how it works.
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