Database Articles - Page 451 of 671

The _id in MongoDB is a field, which is mandatory. In MongoDB, each document stored in a collection requires a unique _id field that acts as a primary key. Following is the syntax to get the array of all the ids i.e. _id in MongoDBdb.yourCollectionName.find({ _id : { $in : [yourValue1, yourValue2, yourValue3, .......N] } } );Let us first implement the following query to create a collection with documents> db.selectInWhereIdDemo.insertOne({"_id":23}); { "acknowledged" : true, "insertedId" : 23 } > db.selectInWhereIdDemo.insertOne({"_id":28}); { "acknowledged" : true, "insertedId" : 28 } > db.selectInWhereIdDemo.insertOne({"_id":45}); { "acknowledged" : true, "insertedId" : 45 } > db.selectInWhereIdDemo.insertOne({"_id":75}); ... Read More

In MongoDB, there is no concept of columns since MongoDB is schema-less and does not contain tables. It contains the concept of collections and a collection has different types of documents to store items.Let us see the syntax −db.yourCollectionName.insertOne({“YourFieldName”:yourValue, “yourFieldName”:”yourValue”, .......N});If you want a single record from a collection, you can use findOne() and in order to get all records from the collection, you can use find().The syntax is as follows −db.yourCollectionName.findOne(); //Get Single Record db.yourCollectionName.find(); // Get All RecordTo understand the above syntax, let us create a collection with the document. The query to create a collection with a ... Read More

You can switch from one database to another using the use command. Here, we are using the collection in the “test” database. Let us insert that collection in another database with the name “sample”.To understand further, let us create a collection with the document. The query to create a collection with a document is as follows −> db.insertOneRecordDemo.insertOne({"UserName":"Larry", "UserAge":23}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9534de16f542d757e2b452") } > db.insertOneRecordDemo.insertOne({"UserName":"Chris", "UserAge":26}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9534e816f542d757e2b453") } > db.insertOneRecordDemo.insertOne({"UserName":"David", "UserAge":25}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9534f116f542d757e2b454") }Display all documents from a collection ... Read More

To get the last access time, try the following syntax −SELECT update_time FROM INFORMATION_SCHEMA.TABLES WHERE table_schema = 'yourDatabaseName' AND table_name = 'yourTableName'The above syntax gives the last access information about MyISAM engine type.Here, our database is ‘business’ and we will be using the table with the name ‘twoprimarykeytabledemo'.To get last access time of MySQL database, use the following query.Case 1 − The query is as follows −mysql> SELECT update_time    -> FROM INFORMATION_SCHEMA.TABLES    -> WHERE table_schema = 'business'    -> AND table_name = 'twoprimarykeytabledemo';The output is as follows −+---------------------+ | UPDATE_TIME ... Read More

The smallest datatype for one bit can be bit(1). The syntax is as follows −yourColumnName bit(1)To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table bitDemo    -> (    -> isValid bit(1)    -> ); Query OK, 0 rows affected (0.49 sec)Now you can check all the details of table with the help of SHOW CREATE command. The query is as follows −mysql> show create table bitDemo;Here is the output −+---------+-----------------------------------------------------------------------------------------------------------------------------+ | Table   | Create Table   ... Read More

MongoDB order the docs in one collection with the help of a $natural operator. It stores the document as it is when we get from find(). The default order is $natural. Let us now see the syntax −db.yourCollectionName.find().sort({ "$natural": 1 });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.orderDocsDemo.insertOne({"UserScore":87}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9531a316f542d757e2b44b") } > db.orderDocsDemo.insertOne({"UserScore":98}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9531a816f542d757e2b44c") } > db.orderDocsDemo.insertOne({"UserScore":99}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9531b216f542d757e2b44d") ... Read More

The localhost means you can access from same machine while from % the remote host access is possible. The syntax is as follows to change the user password.SET PASSWORD FOR 'yourUserName'@'localhost' ='yourPassword';First check the user and host from MySQL.user table. The query is as follows −mysql> select user, host from MySQL.user;Here is the output −+------------------+-----------+ | user             | host      | +------------------+-----------+ | Bob              | %       | | Manish | % ... Read More

First of all, you need to get your collection with the help of getCollectionNames().The database name is “test”. Let us loop through all MongoDB collections and execute the query. The query is as follows −> db.getCollectionNames().forEach(function(collectioNameDemo) ... {    ... var nextDemo = db[(collectioNameDemo) ].find().sort({_id:-1}).limit(1);    ... if (nextDemo.hasNext())    ... {       ... printjson(nextDemo.next()._id.getTimestamp());    ... } ... });The following is the output −ISODate("2019-02-21T18:52:43Z") ISODate("2019-03-19T17:49:00Z") ISODate("2019-03-06T15:40:12Z") ISODate("2019-03-15T16:31:50Z") ISODate("2019-02-21T15:40:52Z") ISODate("2019-03-06T06:14:37Z") ISODate("2019-02-21T19:29:15Z") ISODate("2019-03-15T13:35:33Z") ISODate("2019-03-14T21:13:58Z") ISODate("2019-03-18T22:02:54Z") ISODate("2019-03-22T18:01:45Z") ISODate("2019-03-06T16:21:14Z") ISODate("2019-02-20T15:04:32Z") ISODate("2019-03-06T07:45:42Z") ISODate("2019-03-19T12:33:17Z") ISODate("2019-03-20T21:39:21Z") ISODate("2019-03-15T16:44:26Z") ISODate("2019-03-22T06:20:45Z") ISODate("2019-02-21T16:40:55Z") ISODate("2019-02-21T12:45:20Z") ISODate("2019-03-06T16:05:48Z") ISODate("2019-03-06T16:00:08Z") ISODate("2019-02-28T12:43:56Z") ISODate("2019-03-20T22:11:41Z") ISODate("2019-03-06T05:56:45Z") ISODate("2019-03-06T07:34:12Z") ISODate("2019-03-14T21:00:16Z") ISODate("2019-02-28T10:33:39Z") ISODate("2019-03-06T05:11:10Z") ISODate("2019-02-28T09:44:28Z") ISODate("2019-03-06T10:13:22Z") ISODate("2019-03-17T21:35:26Z")Read More

To select timestamp as date string in MySQL, the syntax is as follows −select FROM_UNIXTIME(yourColumnName, '%Y-%m-%d %H:%i:%s') from yourTableName;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table select_timestampDemo    -> (    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> ArrivalDateTime int    -> ); Query OK, 0 rows affected (0.62 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into select_timestampDemo(ArrivalDateTime) values(1546499730); Query OK, 1 row affected (0.18 sec) mysql> insert into select_timestampDemo(ArrivalDateTime) values(1546210820); Query OK, 1 ... Read More

To understand the query on list field, and/or, you can create a collection with documents.The query to create a collection with a document is as follows −> db.andOrDemo.insertOne({"StudentName":"Larry", "StudentScore":[33, 40, 50, 60, 70]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9522d316f542d757e2b444") } > db.andOrDemo.insertOne({"StudentName":"Larry", "StudentScore":[87, 67, 79, 98, 90]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c95230916f542d757e2b445") }Display all documents from a collection with the help of find() method. The query is as follows −> db.andOrDemo.find().pretty();The following is the output −{    "_id" : ObjectId("5c9522d316f542d757e2b444"),    "StudentName" : "Larry",    "StudentScore" : [       33,   ... Read More