Is it possible to use variables in cql commands in cql scripts?

问题

Is there a way to pass variables in CQL commands when being used in CQL scripts like:

select * from "Column Family Name" where "ColumnName"='A variable which takes different values';

Any suggestions are welcome.

回答1:

No, CQL really doesn't have a way to define variables, run a loop, and update/query based on those variables.

As an alternative, I typically use the DataStax Python driver for simple tasks/scripts like this. Here is an excerpt from a Python script I used a while back to populate product colors from a CSV file.

# connect to Cassandra
auth_provider = PlainTextAuthProvider(username='username', password='currentHorseBatteryStaple')
cluster = Cluster(['127.0.0.1'], auth_provider=auth_provider)
session = cluster.connect('products')

# prepare statements
preparedUpdate = session.prepare(
    """
        UPDATE products.productsByItemID SET color=? WHERE itemid=? AND productid=?;
    """
)
# end prepare statements

counter = 0

# read csv file
dataFile = csv.DictReader(csvfilename, delimiter=',')
for csvRow in dataFile:
    itemid = csvRow['itemid']
    color = csvRow['customcolor']
    productid = csvRow['productid']

    #update product color
    session.execute(preparedUpdate,[color,itemid,productid])

    counter = counter + 1

# close Cassandra connection
session.cluster.shutdown()
session.shutdown()

print "updated %d colors" % (counter)

For more information, check the DataStax tutorial Getting Started with Apache Cassandra and Python.

回答2:

Yes, you can pass variable in the following way:

import com.datastax.spark.connector.{SomeColumns, _}

import org.apache.spark.{SparkConf, SparkContext}

import com.datastax.spark.connector.cql.CassandraConnector

import org.apache.spark.SparkConf

import com.datastax.spark.connector

import com.datastax.spark.connector._

import org.apache.spark.{Logging, SparkConf}

import org.apache.spark.sql.DataFrame

import org.apache.spark.sql.{Row, SQLContext, DataFrame}

import org.apache.spark.sql.cassandra._

val myvar=1

csc.setKeyspace("test_keyspace")

val query="""select a.col1, c.col4, b.col2 from test_keyspace.table1 a inner join test_keyspace.table2 b on a.col1=b.col2 inner join  test_keyspace.table3 c on b.col3=c.col4  where a.col1="""+myvar.toString

val results=csc.sql(query)

results.show()

来源：https://stackoverflow.com/questions/30373893/is-it-possible-to-use-variables-in-cql-commands-in-cql-scripts

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