获取 PSQLException：错误：在带有 Postgres 的 spark jdbc 中使用查询而不是表名时在“SELECT”处或附近出现语法错误

Posted 2023-03-27

【中文标题】获取 PSQLException：错误：在带有 Postgres 的 spark jdbc 中使用查询而不是表名时在“SELECT”处或附近出现语法错误

【英文标题】：Getting PSQLException: ERROR: syntax error at or near "SELECT" when using a query instead of tablename in spark jdbc with Postgres

【发布时间】：2020-03-20 23:06:07

【问题描述】：

对于以下通用sql：

 showTablesSql =  """SELECT table_catalog,table_schema,table_name
    FROM information_schema.tables
    ORDER BY table_schema,table_name"""

当它被提交到spark jdbc for postgresql 时，会发生以下异常：

py4j.protocol.Py4JJavaError: An error occurred while calling o34.load.
: org.postgresql.util.PSQLException: ERROR: syntax error at or near "SELECT"
  Position: 15
    at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2578)

这是正在使用的代码：

url =  f"jdbc:postgresql://c['db.host']/c['db.name']?user=c['db.user']&password=c['db.password']"
print(url)
empDF = spark.read \
    .format("jdbc") \
    .option("url", url) \
    .option("dbtable", showTablesSql) \
    .option("user", c['db.user']) \
    .option("password", c['db.password']) \
    .load()

以下是堆栈跟踪详细信息：

Setting default log level to "WARN".
To adjust logging level use sc.setLogLevel(newLevel). For SparkR, use setLogLevel(newLevel).
jdbc:postgresql://localhost/bluej?user=bluej&password=mypassword
Traceback (most recent call last):
  File "/git/bluej/fusion/python/pointr/bluej/util/sparkmgr.py", line 37, in <module>
    tab = readTab(db, tname)
  File "/git/bluej/fusion/python/pointr/bluej/util/sparkmgr.py", line 23, in readTab
    empDF = spark.read \
  File "/shared/spark3/python/pyspark/sql/readwriter.py", line 166, in load
    return self._df(self._jreader.load())
  File "/shared/spark3/python/lib/py4j-0.10.8.1-src.zip/py4j/java_gateway.py", line 1285, in __call__
  File "/shared/spark3/python/pyspark/sql/utils.py", line 98, in deco
    return f(*a, **kw)
  File "/shared/spark3/python/lib/py4j-0.10.8.1-src.zip/py4j/protocol.py", line 326, in get_return_value
py4j.protocol.Py4JJavaError: An error occurred while calling o34.load.
: org.postgresql.util.PSQLException: ERROR: syntax error at or near "SELECT"
  Position: 15
    at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2578)
    at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:2313)
    at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:331)
    at org.postgresql.jdbc.PgStatement.executeInternal(PgStatement.java:448)
    at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:369)
    at org.postgresql.jdbc.PgPreparedStatement.executeWithFlags(PgPreparedStatement.java:159)
    at org.postgresql.jdbc.PgPreparedStatement.executeQuery(PgPreparedStatement.java:109)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCRDD$.resolveTable(JDBCRDD.scala:61)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCRelation$.getSchema(JDBCRelation.scala:226)
    at org.apache.spark.sql.execution.datasources.jdbc.JdbcRelationProvider.createRelation(JdbcRelationProvider.scala:35)
    at org.apache.spark.sql.execution.datasources.DataSource.resolveRelation(DataSource.scala:339)
    at org.apache.spark.sql.DataFrameReader.loadV1Source(DataFrameReader.scala:240)
    at org.apache.spark.sql.DataFrameReader.$anonfun$load$2(DataFrameReader.scala:229)
    at scala.Option.getOrElse(Option.scala:189)
    at org.apache.spark.sql.DataFrameReader.load(DataFrameReader.scala:229)
    at org.apache.spark.sql.DataFrameReader.load(DataFrameReader.scala:179)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:244)
    at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:357)
    at py4j.Gateway.invoke(Gateway.java:282)
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
    at py4j.GatewayConnection.run(GatewayConnection.java:238)
    at java.base/java.lang.Thread.run(Thread.java:834)

【问题讨论】：

是否可以临时设置log_statement = all 并找出发送到 Postgres 的确切查询？似乎很奇怪，它在位置 15 处有语法错误

是的，该位置位于表名的中间。我会试试的。现在重新启动 pg 服务器

实际上，您可能甚至不需要设置log_statement = all -- log_min_error_statement 默认应该为您记录查询。只需查看您的 postgres 日志并找出收到的实际查询

我重新启动了具有更高日志记录的数据库 - 并且启动时那里有条目。但是我只是重新运行了几次上述查询没有条目。有什么想法为什么他们不会生成日志条目？

我相信你应该像在 sql from 子句中那样在括号“(Select ... )”中编写子查询。

【参考方案1】：

@BjarniRagnarsson 在评论中提到dbtable 实际上是subquery。我从受人尊敬的@zero323 中找到了一些相关信息 https://***.com/a/32629170/1056563

由于 dbtable 被用作 SELECT 语句的源，因此它的格式对普通 SQL 查询有效。如果你想使用子查询，你应该在括号中传递一个查询并提供一个别名：

USING org.apache.spark.sql.jdbc
OPTIONS (
    url "jdbc:postgresql:dbserver",
    dbtable "(SELECT * FROM mytable) tmp"
);

在将 sql 设为 subquery 后，我看到它已正确解析：还没有数据返回，但很可能会出现。