To find a document with Objectid in MongoDB, use the following syntax −db.yourCollectionName.find({"_id":ObjectId("yourObjectIdValue")}).pretty();To understand the above syntax, let us create a collection with the document. The query to create a collection with a document is as follows −> db.findDocumentWithObjectIdDemo.insertOne({"UserName":"Larry"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c90e4384afe5c1d2279d69b") } > db.findDocumentWithObjectIdDemo.insertOne({"UserName":"Mike", "UserAge":23}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c90e4444afe5c1d2279d69c") } > db.findDocumentWithObjectIdDemo.insertOne({"UserName":"Carol", "UserAge":26, "UserHobby":["Learning", "Photography"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c90e4704afe5c1d2279d69d") }Display all documents from a collection with the help of find() method. The query is as follows −> db.findDocumentWithObjectIdDemo.find().pretty();The following is the output ... Read More

Yes, deleting row from view delete row from base table. Let us understand this by creating a new table. The query to create a table is as followsmysql> create table deleteFromBaseTableDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(20) -> ); Query OK, 0 rows affected (0.83 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into deleteFromBaseTableDemo(Name) values('John'); Query OK, 1 row affected (0.18 sec) mysql> insert into deleteFromBaseTableDemo(Name) values('Carol'); Query OK, 1 row affected ... Read More

To get distinct values and count them, you can use GROUP BY clause.The syntax is as followsselect yourColumnName, count(*) as anyAliasName from yourTableName group by yourColumnName;To understand the above syntax, let us create a table. The query to create a table is as followsmysql> create table GroupByAndCountDemo    -> (    -> ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> ClientName varchar(100)    -> ); Query OK, 0 rows affected (0.64 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into GroupByAndCountDemo(ClientName) values('John'); Query OK, 1 row affected (0.18 sec) mysql> insert ... Read More

To understand the concept, let us first create a table. The query to create a table is as followsmysql> create table ReorderSortDemo -> ( -> UserId int -> ); Query OK, 0 rows affected (0.57 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into ReorderSortDemo values(14); Query OK, 1 row affected (0.13 sec) mysql> insert into ReorderSortDemo values(4); Query OK, 1 row affected (0.10 sec) mysql> insert into ReorderSortDemo values(6); Query OK, 1 row affected (0.11 sec) mysql> insert into ReorderSortDemo values(3); Query ... Read More

You can use COALESCE() function for this. In the COALESCE() function, it returns the first NON NULL value from the column. To understand the concept, let us first create a demo tablemysql> create table combineTwoColumnsDemo    -> (    -> UserId int,    -> UserName varchar(20),    -> UserAge int    -> ); Query OK, 0 rows affected (1.12 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into combineTwoColumnsDemo values(101, 'John', 23); Query OK, 1 row affected (0.16 sec) mysql> insert into combineTwoColumnsDemo values(102, 'Carol', 20); Query OK, 1 row affected (0.14 ... Read More

To avoid duplicate entries in MongoDB, you can use createIndex(). The syntax is as follows −db.yourCollectionName.createIndex({"yourFieldName":1}, {unique:true});Let us implement the above syntax. The query to avoid duplicate entries in MongoDB is a follows −> db.avoidDuplicateEntriesDemo.createIndex({"UserName":1}, {unique:true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 }Now insert some records in the above collection. The query to insert record is as follows −> db.avoidDuplicateEntriesDemo.insertOne({"UserName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c90e1824afe5c1d2279d697") }Here is the error whenever you try to insert the same record once again −> db.avoidDuplicateEntriesDemo.insertOne({"UserName":"John"}); 2019-03-19T18:03:08.465+0530 E QUERY [js] ... Read More

You can use aggregate function SUM() along with IF to determine if a value appears in a GROUP BY group.Let us first create a demo tablemysql> create table GroupbygroupDemo -> ( -> UserId int, -> UserName varchar(20) -> ); Query OK, 0 rows affected (1.48 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into GroupbygroupDemo values(10, 'John'); Query OK, 1 row affected (0.14 sec) mysql> insert into GroupbygroupDemo values(10, 'Carol'); Query OK, 1 row affected (0.08 sec) mysql> insert into ... Read More

You can stop rounding decimal field with the help of DECIMAL() function. Here is the demo of a rounded decimal field. For our example, let us first create a demo tablemysql> create table stopRoundingDemo    -> (    -> Amount DECIMAL(7)    -> ); Query OK, 0 rows affected (0.67 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into stopRoundingDemo values(7836.783); Query OK, 1 row affected, 1 warning (0.43 sec) mysql> insert into stopRoundingDemo values(1737.67); Query OK, 1 row affected, 1 warning (0.23 sec) mysql> insert into stopRoundingDemo values(110.50); Query OK, 1 ... Read More

MongoDB is better when you are querying array elements. Let us use the following syntax for querying array elements −db.yourCollectionName.find({yourArrayFieldName:"yourValue"}).pretty();The above syntax will return all those documents which have the value “yourValue” in an array field.To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −> db.queryArrayElementsDemo.insertOne({    ... "StudentName":"John", "StudentFavouriteSubject":["C", "Java"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c90c0354afe5c1d2279d694") } > db.queryArrayElementsDemo.insertOne({ "StudentName":"Carol", "StudentFavouriteSubject":["C", "C++"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c90c0434afe5c1d2279d695") } > db.queryArrayElementsDemo.insertOne({ "StudentName":"David", "StudentFavouriteSubject":["MongoDB", "Java"]}); {    "acknowledged" : ... Read More

You can use CONCAT() function to set date and time fields to get DATETIME field.Let us create a demo tablemysql> create table getDateTimeFieldsDemo -> ( -> ShippingDate date, -> ShippingTime time, -> Shippingdatetime datetime -> ); Query OK, 0 rows affected (0.50 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into getDateTimeFieldsDemo(ShippingDate, ShippingTime) values('2018-01-21', '09:45:34'); Query OK, 1 row affected (0.16 sec) mysql> insert into getDateTimeFieldsDemo(ShippingDate, ShippingTime) values('2013-07-26', '13:21:20'); Query OK, 1 row affected (0.13 sec) mysql> ... Read More