--query 下 $CONDITIONS 的目的是什么? [英] What is the purpose of $CONDITIONS under --query?

问题描述

我使用的是 cloudera 快速入门版 CDH 5.7

I am using cloudera quick start edition CDH 5.7

我在终端窗口上使用了以下查询:

I used below query on terminal window:

sqoop import \
  --connect "jdbc:mysql://quickstart.cloudera:3306/retail_db" \
  --username=retail_dba \
  --password=cloudera \
  --query="select * from orders join order_items on orders.order_id = order_items.order_item_order_id where \$CONDITIONS" \
  --target-dir /user/cloudera/order_join \
  --split-by order_id \
  --num-mappers 4

问:$CONDITIONS 的目的是什么?为什么在这个查询中使用?谁能给我解释一下.

Q: What is the purpose of the $CONDITIONS ? Why used in this query ? Can anybody can explain to me.

推荐答案

$CONDITIONS 用于 sqoop 内部修改查询，实现任务拆分和获取元数据.

$CONDITIONS is used internally by sqoop to modify query to achieve task splitting and fetching metadata.

为了获取元数据，sqoop 将 \$CONDITIONS 替换为 1= 0

To fetch metadata, sqoop replaces \$CONDITIONS with 1= 0

select * from table where 1 = 0

为了获取所有数据(1 个映射器)，sqoop 将 \$CONDITIONS 替换为 1= 1

To fetch all data (1 mapper), sqoop replaces \$CONDITIONS with 1= 1

select * from table where 1 = 1

在多个映射器的情况下，sqoop 用范围查询替换 \$CONDITIONS 以从 RDBMS 获取数据的子集.

In the case of multiple mappers, sqoop replaces \$CONDITIONS with range query to fetch a subset of data from RDBMS.

例如，id 介于 1 到 100 之间，我们使用了 4 个映射器.

For example, id lies between 1 to 100 and we are using 4 mappers.

Select * From table WHERE id >= 1' AND 'id < 25
Select * From table WHERE id >= 25' AND 'id < 50
Select * From table WHERE id >= 50' AND 'id < 75
Select * From table WHERE id >= 75' AND 'id <= 100

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