Moreover, we will discuss keyspace in Cassandra and its various commands like\u00a0Create Keyspace, Use, Alter Keyspace, Drop Keyspace, Create Table, Alter Table, Truncate Table, Drop Table,\u00a0 Create Index, and Drop Index. In addition, we will discuss each command with their syntax & example. <\/span><\/span><\/span><\/p>\n So, let’s start Data Definition command – CQL.<\/span><\/span><\/span><\/p>\n Data Definition Command – Cassandra Query Language<\/p><\/div>\n Do you know top Cassandra Terminologies<\/a><\/strong><\/p>\n Data definition command are used for defining the data in the database. They are another type of commands used in cqlsh prompt. In other words, they are used to create data and data storage units in the database. These commands basically are used to create and manipulate keyspace, table,\u00a0<\/span><\/span><\/span>and index.<\/span><\/p>\n In Cassandra Data definition Command, Keyspace is basically a namespace that defines data replication on nodes. There are many clusters in a Cassandra database. Every Cassandra cluster contains one keyspace per node. This keyspace is created and altered using Data Definition Command.<\/span><\/span><\/span> This command is used to create a keyspace. Every system specifies a node. This system or node has a keyspace. This keyspace is a storage unit for the data. Data definition command help to create keyspace. The statement has two main properties that are replication and durable writes. The replication property includes class and replication factor. For the class property, the user has to enter the strategy name. <\/span><\/span><\/span><\/p>\n For the replication factor, the user has to enter the number of replicas that have to be made. The durable_writes property includes the boolean values. These properties are optional. A user may or may not use these properties.<\/span><\/span><\/span><\/p>\n Have a look at Cassandra Cluster<\/a><\/strong> Example:<\/strong> Let us create a keyspace named ‘keyspace 1’ with simple strategy and 2 number of replicas. The durable writes for this keyspace is false.<\/span><\/span><\/span><\/p>\n This command in Data Definition Command, is used to use a keyspace stored in a database. Cassandra uses keyword ‘USE’ to perform the following function. Example:<\/strong> Let’s discuss Cassandra API<\/a><\/strong><\/p>\n This command is used to alter the properties of the keyspace. ALTER KEYSPACE command is used to do the operation. A user can alter replication and durable_writes properties.\u00a0Data definition command help\u00a0to\u00a0alter keyspace.\u00a0<\/span><\/span><\/span> or<\/span><\/span><\/span><\/p>\n Example:<\/strong> Let us alter the properties of keyspace1 from simple strategy to network topology strategy. The number of replicas, from 2 to 5 and boolean type, from false to true.<\/span><\/span><\/span><\/p>\n Let’s See Cassandra Curd Operation \u2013 Create, Update, Read & Delete in Detail<\/a><\/strong><\/p>\n This command lets the user drop a keyspace. In other words, the user deletes the keyspace using this. To perform this operation we use DROP KEYSPACE keyword. Example:<\/strong> Let us delete the keyspace we developed in the previous example. A table is one of the most important storage units in Cassandra Database. The user has the ability to create a table that can be deployed to the Cassandra database.<\/span><\/span><\/span><\/p>\n Have a look at Cassandra Troubleshooting<\/a><\/strong> The statement allowed the user to set field name and their respective field type and also the primary. The primary key is basically a main column that is used for identification of a row.<\/span><\/span><\/span> EXAMPLE:<\/strong> Let us create a table ‘student ‘ with fields, name, age, id, and branch. Primary key is id.<\/span><\/span><\/span><\/p>\n A User can change the properties of the table. We use ALTER TABLE command to perform the following operation. The user can perform two operations, add a column and drop a column.<\/span><\/span><\/span> Read About Architecture of\u00a0Cassandra in Detail<\/a><\/strong><\/p>\n To add a column the user can use the following syntax. to drop a column user can use the following syntax. Example:<\/strong> Let us alter the table student. In the table, we will add a column of a city and drop the column age.<\/span><\/span><\/span> If a table is not required by the user, the user can truncate the whole table. The keyword used to truncate the table is TRUNCATE. When the user truncates the table, all the entry in the rows is deleted. The table stays but with zero rows.<\/span><\/span><\/span><\/p>\n Let’s revise Cassandra User-Defined Types<\/a><\/strong> Example:<\/strong> Let’s truncate the table student. Do you know How Cassandra Stores Data –\u00a0Cassandra Data Model<\/a><\/strong><\/p>\n If the user wants to completely delete the table from the database, the user can use this command. We use DROP TABLE keyword to perform the following operation.<\/span><\/span><\/span> Example:<\/strong> In this example, we will delete the table student. The user can set an index on a field in a table. We use CREATE INDEX keyword to perform the following operation.<\/span><\/span> Example:<\/strong> In this example, we will create an index on ‘id’ at table ‘student’. Have a look at Cassandra Built-in Collection<\/a><\/strong><\/p>\n A user\u00a0can drop the set index on the field in a table. A user can use DROP INDEX keyword to perform the function.\u00a0Data Definition Command plays main role in it.\u00a0<\/span><\/span><\/span> Example:<\/strong> In this example, we will drop the index on ‘id’ at table ‘student’. Let’s Explore\u00a0Applications of Cassandra in Detail<\/a><\/strong> Hence, in this CQL tutorial, we studied Data definition Command in Cassandra Query Langauge (CQL), Create keyspace, use, alter keyspace, drop\u00a0keyspace, create table, alter table, truncate table, drop table, create index, and drop index with examples and syntax.<\/p>\n These data definition commands help to create & alter Cassandra keyspace, table, and index.<\/p>\n Furthermore, if you have any query regarding CQL Data definition Command, feel free to ask in the\u00a0command box.![\"Data](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2018\/05\/data-definition-command-01.jpg\")
<\/a>2. CQL – Data Definition Command<\/h2>\n
3. Cassandra Keyspace<\/h2>\n
\nDo you know\u00a0 Major Difference & Similarities Between\u00a0HBase vs Cassandra<\/a><\/strong><\/p>\na. Create Keyspace<\/h3>\n
\nSYNTAX:<\/strong><\/span><\/span><\/span><\/p>\nCREATE KEYSPACE <keyspace name> WITH <properties> AND <properties>\r\n<\/pre>\n
\nFULL SYNTAX:<\/span><\/span><\/strong><\/span><\/p>\nCREATE KEYSPACE 'keyspace name'\r\nWITH replication{'class':'<strategy name>','replication factor':'<number of replicas>'}\r\nAND durable_writes='<Boolean value>';<\/pre>\ncqlsh> CREATE KEYSPACE 'keyspace1'\r\n... WITH replication{'class':'simple strategy','replication factor':'2'}\r\n... AND durable_writes='false';<\/pre>\nb. Use<\/h3>\n
\nSYNTAX:<\/strong><\/span><\/span><\/span><\/p>\nUSE<keyspace name>\r\n<\/pre>\n
\nLet us use the keyspace ‘keyspace1’ that we made in the earlier example.<\/span><\/span><\/span><\/p>\ncqlsh>USE keyspace1;\r\ncqlsh; keyspace1><\/pre>\n
c. Alter Keyspace<\/h3>\n
\nSYNTAX:<\/strong><\/span><\/span><\/span><\/p>\nALTER KEYSPACE <keyspace name> WITH <properties> AND <properties><\/pre>\n
ALTER KEYSPACE <keyspace name>\r\nWITH replication={'class':'strategy name','replication factor':'number of replicas'}\r\nAND durable_writes=<'boolean type'>;\\<\/pre>\ncqlsh> ALTER KEYSPACE keyspace1\r\n... WITH replication{'class':'NetworkTopologyStrategy','no. of replicas':'5'}\r\n... AND durable_writes= true;<\/pre>\nd. Drop Keyspace<\/h3>\n
\nSYNTAX:<\/strong>
\n<\/span><\/span><\/span><\/p>\nDROP KEYSPACE<keyspace name>;<\/pre>\n
\n<\/span><\/span><\/span><\/p>\ncqlsh> DROP KEYSPACE keyspace1;<\/pre>\n
e. Create Table<\/h3>\n
\nSYNTAX:<\/strong>
\n<\/span><\/span><\/span><\/p>\nCREATE TABLE\/COLUMN FAMILY<table name>\r\n('<column-definition>','<columan-definition>')\r\n(WITH<option>AND<option>)<\/pre>\n
\nFULL SYNTAX:<\/span><\/span><\/strong><\/span><\/p>\nCREATE TABLE <table name>\r\n<field name1> <field type1>\r\n<field name2> <field type2>\r\n<field name3> <field type3>\r\nprimary key(<field name>);<\/pre>\n
cqlsh;keyspace1> CREATE TABLE student\r\n... name text,\r\n... age int,\r\n... id int,\r\n... branch text,\r\n... primary key (id);<\/pre>\n
f. Alter Table<\/h3>\n
\nSYNTAX:<\/strong>
\n<\/span><\/span><\/span><\/p>\nALTER TABLE\/COLUMN FAMILY <table name><instruction>;<\/pre>\n
i. Add a column<\/span><\/span><\/b><\/span><\/span><\/h4>\n
\n<\/span><\/span><\/span><\/p>\nALTER TABLE <table name>\r\nADD <new column> <data type>;<\/pre>\n
ii. Drop a column<\/span><\/span><\/b><\/span><\/span><\/h4>\n
\n<\/span><\/span><\/span><\/p>\nALTER TABLE <table name>\r\nDROP <column name>;<\/pre>\n
\nALTER TABLE student
\n<\/span><\/span><\/span><\/p>\nADD city text;\r\nALTER TYPE student\r\nDROP age;<\/pre>\n
g. Truncate Table<\/h3>\n
\nSYNTAX:<\/strong>
\n<\/span><\/span><\/span><\/p>\nTRUNCATE<table name>;<\/pre>\n
\n<\/span><\/span><\/span><\/p>\nTRUNCATE student;<\/pre>\n
h. Drop Table<\/h3>\n
\nSYNTAX:<\/strong>
\n<\/span><\/span><\/span><\/p>\nDROP TABLE<table name>;<\/pre>\n
\n<\/span><\/span><\/span><\/p>\nDROP TABLE student;<\/pre>\n
i. Create Index<\/h3>\n
\nSYNTAX:<\/strong>
\n<\/span><\/span><\/p>\nCREATE INDEX <field name> ON <table name><\/pre>\n
\n<\/span><\/span><\/span><\/p>\ncqlsh;keyspcae1> CREATE INDEX id ON student;<\/pre>\n
j. Drop Index<\/h3>\n
\nSYNTAX:<\/strong>
\n<\/span><\/span><\/span><\/p>\nDROP INDEX <field name>;<\/pre>\n
\n<\/span><\/span><\/span><\/p>\ncqlsh;keyspcae1> DROP INDEX id;<\/pre>\n
\nSo, this was all about CQL-Data Definition Command Tutorial. Hope you like our explanation.<\/p>\n4. Conclusion<\/h2>\n
\nRelated Topic- Cassandra Interview Questions<\/a><\/strong>
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