Documentation

columninfo

Retrieve column information from ApacheCassandradatabase table

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Syntax

cols = columninfo(conn,keyspace,tablename)
[cols,keyValues] = columninfo(conn,keyspace,tablename)

Description

example

cols= columninfo(conn,keyspace,tablename)returns column information from a specified Cassandra®database table in a specified keyspace using the Cassandra database connection.

example

[cols,keyValues] = columninfo(conn,keyspace,tablename)also returns the key values for each partition in the Cassandra database table.

Examples

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This example uses:

Open Live Script

Using a Cassandra® database connection, return column information for a Cassandra database table. Specify the keyspace and the name of the table. In this case, the Cassandra database has theemployeedatakeyspace, which contains theemployees_by_jobdatabase table.

Create a Cassandra database connection using the local host address.connis acassandraobject.

contactPoints =“localhost”; conn = cassandra(contactPoints);

Return column information for theemployees_by_jobdatabase table in theemployeedatakeyspace.

keyspace ="employeedata"; tablename ="employees_by_job"; cols = columninfo(conn,keyspace,tablename);

Display the first few rows of column information.

head(cols)
ans=8×4 table数据类型名称PartitionKey ClusteringColumn __________________ ________ ____________ ________________ "job_id" "text" true "" "hire_date" "date" false "DESC" "employee_id" "int" false "ASC" "commission_pct" "double" false "" "department_id" "int" false "" "email" "text" false "" "first_name" "text" false "" "last_name" "text" false ""

colsis a table with these variables:

  • Name— Cassandra database column name

  • DataType— Cassandra Query Language (CQL) data type of the Cassandra database column

  • PartitionKey— Partition key indicator

  • ClusteringColumn— Clustering column indicator

Close the Cassandra database connection.

close(conn)

This example uses:

Open Live Script

Using a Cassandra® database connection, return partition key values for a Cassandra database table. Specify the keyspace and name of the table. In this case, the Cassandra database has theemployeedatakeyspace, which contains theemployees_by_jobdatabase table.

Create a Cassandra database connection using the local host address.connis acassandraobject.

contactPoints =“localhost”; conn = cassandra(contactPoints);

Return column information for theemployees_by_jobdatabase table in theemployeedatakeyspace.

keyspace ="employeedata"; tablename ="employees_by_job"; [cols,keyValues] = columninfo(conn,keyspace,tablename);

keyValuesis a table that contains a variable for each partition key. The rows are partition key values.

Display the first few partition key values of the Cassandra database table.

head(keyValues)
ans=8×1 tablejob_id __________ "ST_CLERK" "SA_MAN" "HR_REP" "IT_PROG" "FI_MGR" "PR_REP" "PU_MAN" "AD_PRES"

job_idis the only partition key in theemployees_by_jobdatabase table. Each row is a partition key value that is a unique partition inemployees_by_job.

Use the partition key values with thepartitionReadfunction to import data from a Cassandra database table.

Close the Cassandra database connection.

close(conn)

Input Arguments

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Cassandra database connection, specified as acassandraobject.

Keyspace, specified as a character vector or string scalar. If you do not know the keyspace, then access theKeyspacesproperty of thecassandraobject using dot notation to view the keyspaces in the Cassandra database.

Example:"employeedata"

Data Types:char|string

Cassandra database table name, specified as a character vector or string scalar. If you do not know the name of the table, then use thetablenamesfunction to find it.

Example:"employees_by_job"

Data Types:char|string

Output Arguments

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Column information from a Cassandra database table, returned as a MATLAB®table containing these variables.

Variable Name Variable Description Variable Data Type

Name

Cassandra database column name

string

DataType

CQL data type of the Cassandra database column

string

PartitionKey

Whether the Cassandra database table column is a partition key (trueindicates a partition key)

logical

ClusteringColumn

Whether the Cassandra database table column is a clustering column ("ASC"indicates ascending order,"DESC"indicates descending order, and""indicates that the column is not a clustering column)

string

If the data type of a column in a Cassandra database table is a collection (for example, alist,map, and so on), then the value of theDataTypevariable contains angle brackets (<>). These angle brackets surround the data type of the items in the collection. The value for user-defined types (UDTs) contains the type name. For example, if the UDT isperson, then the value of theDataTypevariable ispersonin the MATLAB table. For details about valid CQL data types, seeCQL data types.

Partition key values, returned as a table. The MATLAB table contains one variable for each partition key in the Cassandra database table. Each row in the MATLAB table represents a unique partition in the Cassandra database table.

You can use the partition key values with thepartitionReadfunction to import data from a Cassandra database table.

For details about the MATLAB data types of the partition key values, seeConvert CQL Data Types to MATLAB Data Types.

See Also

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Topics

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Introduced in R2018b

Database Toolbox Documentation
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