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Articles by Ankith Reddy
Page 61 of 73
Upsert in MongoDB while using custom _id values to insert a document if it does not exist?
You need to use insert() for this. Whenever you insert custom _id values and the document already exist with the custom _id value then an error is visible. Let us first create a collection with documents. Under this, we tried adding the same document again and this resulted in an error> db.customIdDemo.insert({"_id":1, "StudentName":"John"}); WriteResult({ "nInserted" : 1 }) > db.customIdDemo.insert({"_id":1, "StudentName":"Carol"}); WriteResult({ "nInserted" : 0, "writeError" : { "code" : 11000, "errmsg" : "E11000 duplicate key error collection: admin.customIdDemo index: _id_ dup key: { : 1.0 }" } }) > db.customIdDemo.insert({"_id":2, "StudentName":"Carol"}); ...
Read MoreHow to select ID column as null in MySQL?
Let us first create a table. The query to create a table is as followsmysql> create table selectAllDemo - > ( - > Name varchar(100), - > Age int - > ); Query OK, 0 rows affected (1.90 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into selectAllDemo values('John', 25); Query OK, 1 row affected (0.99 sec) mysql> insert into selectAllDemo values('Carol', 26); Query OK, 1 row affected (0.42 sec) mysql> insert into selectAllDemo values('Bob', 30); Query OK, 1 row affected (1.57 ...
Read MoreHow to return only a single property “_id” in MongoDB?
Following is the syntax to return only a single property _id in MongoDBdb.yourCollectionName.find({}, {"_id": 1}).pretty();Let us first create a collection with documents> db.singlePropertyIdDemo.insertOne({"_id":101, "UserName":"Larry", "UserAge":21}); { "acknowledged" : true, "insertedId" : 101 } > db.singlePropertyIdDemo.insertOne({"_id":102, "UserName":"Mike", "UserAge":26}); { "acknowledged" : true, "insertedId" : 102 } > db.singlePropertyIdDemo.insertOne({"_id":103, "UserName":"Chris", "UserAge":24}); { "acknowledged" : true, "insertedId" : 103 } > db.singlePropertyIdDemo.insertOne({"_id":104, "UserName":"Robert", "UserAge":23}); { "acknowledged" : true, "insertedId" : 104 } > db.singlePropertyIdDemo.insertOne({"_id":105, "UserName":"John", "UserAge":27}); { "acknowledged" : true, "insertedId" : 105 }Following is the query to display all documents from a collection with the help of find() method> db.singlePropertyIdDemo.find().pretty();This will produce ...
Read MoreRename Root @ localhost username in MySQL?
The syntax is as follows to rename Root @localhostUPDATE MySQL.user SET user = ‘yourNewRootName’ WHERE user = 'root';To understand the above concept, let us check all the user names and host. The query is as followsmysql> select user, host from MySQL.user;The following is the output+------------------+-----------+ | user | host | +------------------+-----------+ | Bob | % | | Manish | % | | User2 | % ...
Read MoreFind oldest/ youngest post in MongoDB collection?
To find oldest/youngest post in MongoDB collection, you can use sort(). Let’s say you have a document with a field “UserPostDate” and you need to get the oldest and youngest post. For that, Let us first create a collection with documents>db.getOldestAndYoungestPostDemo.insertOne({"UserId":"Larry@123", "UserName":"Larry", "UserPostDate":new ISODate('2019-03-27 12:00:00')}); { "acknowledged" : true, "insertedId" : ObjectId("5c9a700f15e86fd1496b38ab") } >db.getOldestAndYoungestPostDemo.insertOne({"UserId":"Sam@897", "UserName":"Sam", "UserPostDate":new ISODate('2012-06-17 11:40:30')}); { "acknowledged" : true, "insertedId" : ObjectId("5c9a703815e86fd1496b38ac") } >db.getOldestAndYoungestPostDemo.insertOne({"UserId":"David@777", "UserName":"David", "UserPostDate":new ISODate('2018-01-31 10:45:35')}); { "acknowledged" : true, "insertedId" : ObjectId("5c9a705e15e86fd1496b38ad") } >db.getOldestAndYoungestPostDemo.insertOne({"UserId":"Chris@909", "UserName":"Chris", "UserPostDate":new ISODate('2017-04-14 04:12:04')}); { "acknowledged" : true, "insertedId" : ObjectId("5c9a708915e86fd1496b38ae") }Following ...
Read MoreSelect text after last slash in MySQL?
You need to use substring_index() function from MySQL to select text.The syntax is as followsSELECT substring_index(yourColumnName, '/', -1) AS anyAliasName FROM yourTableName;To understand the above concept, let us create a table. The query to create a table is as followsmysql> create table selectTextAfterLastSlashDemo - > ( - > UserId int NOT NULL AUTO_INCREMENT PRIMARY KEY, - > UserPathDirectory varchar(200) - > ); Query OK, 0 rows affected (0.54 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into selectTextAfterLastSlashDemo(UserPathDirectory) values('C:/MyFolder1/MyEntityFramework'); Query OK, 1 ...
Read MoreHow to update MongoDB collection using $toLower?
There is a $toLower operator in MongoDB to be used as part of aggregate framework. But, we can also use the for loop to iterate over the specific field and update one by one.Let us first create a collection with documents> db.toLowerDemo.insertOne({"StudentId":101, "StudentName":"John"}); { "acknowledged" : true, "insertedId" : ObjectId("5c9b1b4515e86fd1496b38bf") } > db.toLowerDemo.insertOne({"StudentId":102, "StudentName":"Larry"}); { "acknowledged" : true, "insertedId" : ObjectId("5c9b1b4b15e86fd1496b38c0") } > db.toLowerDemo.insertOne({"StudentId":103, "StudentName":"CHris"}); { "acknowledged" : true, "insertedId" : ObjectId("5c9b1b5115e86fd1496b38c1") } > db.toLowerDemo.insertOne({"StudentId":104, "StudentName":"ROBERT"}); { "acknowledged" : true, "insertedId" : ObjectId("5c9b1b5a15e86fd1496b38c2") }Following is the query to display all documents from ...
Read MoreHow to operate on all databases from the MongoDB shell?
To operate on all databases from MongoDB shell, you can use listDatabases along with adminCommand().Let’s say we are using a sample database “test”. At first, check the current database with the help of db command.Following is the query to get the current database> db;This will produce the following outputTestFollowing is the query to operate on all the databases from the Mongo shell> var allDatabaseList = db.adminCommand('listDatabases');Now you need to use printjson() in order to print all databases. Following is the query> printjson (allDatabaseList);This will produce the following output{ "databases" : [ { ...
Read MoreMySQL ORDER BY Date field not in date format?
The following is the syntax to order by date field which is not in date formatselect *from yourTableName order by STR_TO_DATE(yourColumnName, '%d/%m/%Y') DESC;To understand the above syntax, let us create a table. The query to create a table is as followsmysql> create table orderByDateFormatDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> ArrivalDatetime varchar(100) -> ); Query OK, 0 rows affected (0.73 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into orderByDateFormatDemo(ArrivalDatetime) values('01/10/2012'); Query OK, 1 row affected (0.20 sec) mysql> insert into orderByDateFormatDemo(ArrivalDatetime) values('03/11/2010'); ...
Read MoreW and Z registers in 8085 Microprocessor
To define Temporary Register, we can mention that it is an 8-bit non-programmable resister used to hold data during an arithmetic and logic operation (temporary resister is used to hold intermediate result). The result is stored in the accumulator, and the flags (flip-flops) are set or reset according to the result of the operation.W and Z are two 8-bit temporary registers of 8085 microprocessor, which is not accessible to the user. They are exclusively used for the internal operation by the microprocessor. These registers are used either to store 8-bit of information in each W and Z registers or a ...
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