如何使用 SQL 查询在 dbtable 中定义表? [英] How to use SQL query to define table in dbtable?
问题描述
在
怎么了?
由于 dbtable
被用作 SELECT
语句的源,它的形式可以对普通 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:
创建临时表 jdbcTable使用 org.apache.spark.sql.jdbc选项 (url "jdbc:postgresql:dbserver",dbtable "(SELECT * FROM mytable) tmp");
它将被传递给数据库:
SELECT * FROM (SELECT * FROM mytable) tmp WHERE 1=0
In JDBC To Other Databases I found the following explanation of dbtable
parameter:
The JDBC table that should be read. Note that anything that is valid in a FROM clause of a SQL query can be used. For example, instead of a full table you could also use a subquery in parentheses.
When I use the code:
CREATE TEMPORARY TABLE jdbcTable
USING org.apache.spark.sql.jdbc
OPTIONS (
url "jdbc:postgresql:dbserver",
dbtable "mytable"
)
everything works great, but the following:
dbtable "SELECT * FROM mytable"
leads to the error:
What is wrong?
Since dbtable
is used as a source for the SELECT
statement it has be in a form which would be valid for normal SQL query. If you want to use subquery you should pass a query in parentheses and provide an alias:
CREATE TEMPORARY TABLE jdbcTable
USING org.apache.spark.sql.jdbc
OPTIONS (
url "jdbc:postgresql:dbserver",
dbtable "(SELECT * FROM mytable) tmp"
);
It will be passed to the database as:
SELECT * FROM (SELECT * FROM mytable) tmp WHERE 1=0
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