columninfo

Retrieve column information from Apache Cassandra database table

Syntax

cols = columninfo(conn,keyspace,tablename)

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

Description

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

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

Examples

Return Column Information from Cassandra Database Table

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 the employeedata keyspace, which contains the employees_by_job database table.

Create a Cassandra database connection using the local host address. conn is a cassandra object.

contactPoints = "localhost";
conn = cassandra(contactPoints);

Return column information for the employees_by_job database table in the employeedata keyspace.

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
          Name          DataType    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             ""         

cols is 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)

Return Partition Key Values from Cassandra Database Table

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 the employeedata keyspace, which contains the employees_by_job database table.

Create a Cassandra database connection using the local host address. conn is a cassandra object.

contactPoints = "localhost";
conn = cassandra(contactPoints);

Return column information for the employees_by_job database table in the employeedata keyspace.

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

keyValues is 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 table
      job_id  
    __________

    "ST_CLERK"
    "SA_MAN"  
    "HR_REP"  
    "IT_PROG" 
    "FI_MGR"  
    "PR_REP"  
    "PU_MAN"  
    "AD_PRES" 

job_id is the only partition key in the employees_by_job database table. Each row is a partition key value that is a unique partition in employees_by_job.

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

Close the Cassandra database connection.

close(conn)

Input Arguments

conn — Cassandra database connection

cassandra object

Cassandra database connection, specified as a cassandra object.

keyspace — Keyspace

character vector | string scalar

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

Example: "employeedata"

Data Types: char | string

tablename — Cassandra database table name

character vector | string scalar

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

Example: "employees_by_job"

Data Types: char | string

Output Arguments

cols — Column information

table

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 (true indicates 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, a list, map, and so on), then the value of the DataType variable 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 is person, then the value of the DataType variable is person in the MATLAB table. For details about valid CQL data types, see CQL data types.

keyValues — Partition key values

table

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 the partitionRead function to import data from a Cassandra database table.

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