[英]Check table exists Spark jdbc
我正在使用 Spark JDBC 從 Microsoft SQL Server 將一些數據讀取到數據框中。 當表不存在時(例如,它被意外刪除)我得到一個異常:com.microsoft.sqlserver.jdbc.SQLServerException:無效的對象名稱'TestAllData'。
我想創建一些機制來首先檢查表是否存在,然后才讀取數據。 有沒有辦法使用 Spark JDBC 來做到這一點? 因為我嘗試使用 Ms sql server 中的 if exists 構造,但它不適用於使用 Spark 進行查詢。
目前,我讀取數據的代碼如下所示:
def getDataQuery() = {
s"(select * from TestData) as subq"
}
def jdbcOptions(dataQuery: String, partitionColumn: String, lowerBound: String, upperBound: String, numPartitions: String) = Map[String,String](
"driver" -> config.getString("sqlserver.db.driver"),
"url" -> config.getString("sqlserver.db.url"),
"user" -> config.getString("sqlserver.db.user"),
"password" -> config.getString("sqlserver.db.password"),
"customSchema" -> config.getString("sqlserver.db.custom_schema"),
"dbtable" -> dataQuery,
"partitionColumn" -> partitionColumn,
"lowerBound" -> lowerBound,
"upperBound" -> upperBound,
"numPartitions" -> numPartitions
)
val dataDF = sparkSession
.read
.format("jdbc")
.options(jdbcOptions(getDataQuery()))
.load()
您可以檢查查詢是否:
def tableExist() = {
s"show tables in default"
}
val existDF = sparkSession
.read
.format("jdbc")
.options(jdbcOptions(tableExist()))
.load()
val dataDF = if (existDF.select("tableName").collect().map(_ (0)).contains("TestData"))
sparkSession
.read
.format("jdbc")
.options(jdbcOptions(getDataQuery()))
.load()
與Pablo López Gallego所寫的概念相同,但適用於 Postgres
object JdbcLoader extends App{
val finalUrl = s"jdbc:postgresql://localhost:5432/my_db?ApplicationName=test"
val user = "user"
val password = "pass"
val sparkConf = new SparkConf()
sparkConf.setMaster(s"local[2]")
val spark = SparkSession.builder().config(sparkConf).getOrCreate()
def loadTable(tableName:String ): DataFrame ={
val opts: Map[String, String] = Map(
"url" -> finalUrl,
"user" -> user,
"password" -> password,
"dbtable" -> tableName
)
spark.sqlContext.
read.
format("jdbc").
options(opts).
load
}
def checkIfTableExists(tableName: String) : Boolean = {
var schema = "public"
var table = tableName
if (tableName.contains(".")){
val schemaAndTable = tableName.split("\\.")
schema = schemaAndTable.head
table = schemaAndTable.last
}
val tableExistQ = s"(SELECT table_name FROM information_schema.tables WHERE table_schema='${schema}'" +
s" AND table_type='BASE TABLE' and table_name = '${table}') as FOO"
val df = loadTable(tableExistQ)
df.count() > 0
}
println(checkIfTableExists("my_schema.users"))
}
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