读取clickhouse数据库数据

import scala.collection.mutable.ArrayBuffer
import java.util.Properties
import org.apache.spark.sql.SaveMode
import org.apache.spark.sql.SparkSessiondef getCKJdbcProperties(batchSize: String = "100000",socketTimeout: String = "300000",numPartitions: String = "50",rewriteBatchedStatements: String = "true"): Properties = {val properties = new Propertiesproperties.put("driver", "ru.yandex.clickhouse.ClickHouseDriver")properties.put("user", "default")properties.put("password", "数据库密码")properties.put("batchsize", batchSize)properties.put("socket_timeout", socketTimeout)properties.put("numPartitions", numPartitions)properties.put("rewriteBatchedStatements", rewriteBatchedStatements)properties}
// 读取click数据库数据
val today = "2023-06-05"
val ckProperties = getCKJdbcProperties()
val ckUrl = "jdbc:clickhouse://233.233.233.233:8123/ss"
val ckTable = "ss.test"
var ckDF = spark.read.jdbc(ckUrl, ckTable, ckProperties)

**show** 展示数据,类似于select * from test的功能

1. [ckDF.show](http://ckDF.show) 默认展示前20个记录
2. ckDF.show(3) 指定展示记录数
3. ckDF.show(false) 是否展示前20个
4. ckDF.show(3, 0) 截取记录数

**ckDF.collect** 方法会将 ckDF中的所有数据都获取到，并返回一个Array对象

ckDF.collectAsList 功能和collect类似，只不过将返回结构变成了List对象

**ckDF.describe**("ip_src").show(3) ****获取指定字段的统计信息

scala> ckDF.describe("ip_src").show(3)
+-------+------+                                                                
|summary|ip_src|
+-------+------+
|  count|855035|
|   mean|  null|
| stddev|  null|
+-------+------+
only showing top 3 rows

first, head, take, takeAsList 获取若干行记录

1. first获取第一行记录
2. head获取第一行记录，head(n: Int)获取前n行记录
3. take(n: Int)获取前n行数据
4. takeAsList(n: Int)获取前n行数据，并以List的形式展现

以Row或者Array[Row]的形式返回一行或多行数据。first和head功能相同。take和takeAsList方法会将获得到的数据返回到Driver端，所以，使用这两个方法时需要注意数据量，以免Driver发生OutOfMemoryError