In MongoDB a collection is automatically created when it is referenced in any command. For example, if you run an insert command : db. student . insert ({ name : " Viraj " }) Above command will create a collection named student if it doesn't exist already in the database. But we can explicitly create a collection using the createCollection() command. The syntax of createCollection method is : db. createCollection ( name , options ) In the above command, name will be the name of the collection and options is a document which can be used to specify configurations for the collection. options parameter is optional, and you can simply create a collection by just providing a name for the collection. But if you want to configure your collection, you can use various options available to do so. Following are the available configuration options for creating a collection in MongoDB : Field Type Description capped boolean (Option...
Hadoop Hive analytic functions compute an aggregate value that is based on a group of rows. A Hadoop Hive HQL analytic function works on the group of rows and ignores the NULL in the data if you specify Hadoop Hive COUNT Analytic Function Returns number of rows in query or group of rows. Syntax: COUNT(column reference | value expression | *) over(window_spec) For Example; select pat_id, dept_id, count(*) over (partition by dept_id order by dept_id asc) as pat_cnt from patient; at_id dept_id pat_cnt 6 111 4 2 111 4 5 111 4 1 111 4 4 222 3 5 222 3 3 222 3 7 333 1 8 444 1 Hadoop Hive SUM Analytic Function Just like count function, sum Hive analytic function is used to compute the sum of columns or expression. Sum analytic function is used to compute the sum of all rows of table or rows within the groups. Syntax: SUM(column | expression) OVER( window_spec) For example: Calculate sum insured amount of all patients within each department...
Modes of Unix Vi Editor The vi editor has three modes of operation viz. the command mode, the insert mode, and the ex-command mode. #1) Command mode: In this mode, all the keys work as commands. These keys are used for inserting, appending, deleting, opening new lines, moving the cursor over the paragraphs and sentences, etc. In this mode, the keys are not displayed but each key performs an operation. By default the vi editor is in command mode, hence we cannot type text in command mode. In order to write programs or text in vi editor, we need to switch to the insert mode which can be done by pressing the escape button. #2) Insert mode: In this mode, we can insert, append, edit or replace texts. We can switch from the command mode to Insert mode by pressing the escape button and then press I or A to enter into insert mode. #3) Ex command mode: This mode is used for entering commands at the bottom line of the vi editor called as a command line. To switch to Ex command ...
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