Question

我正在尝试从包含超过一百万行的CSV提取（从Oracle数据库表生成）创建一个Parquet表。这些行中约有25行的START_DATE值为空，CTAS无法将""解释为null。任何建议将不胜感激。

CREATE TABLE dfs.tmp.FOO as
select cast(columns[0] as INT) as `PRODUCT_ID`,
cast(columns[1] as INT) as `LEG_ID`,
columns[2] as `LEG_TYPE`,
to_timestamp(columns[3], 'dd-MMM-yy HH.mm.ss.SSSSSS a') as `START_DATE`
from dfs.`c:\work\prod\data\foo.csv`;



Error: SYSTEM ERROR: IllegalArgumentException: Invalid format ""

Answer 1

您始终可以包含CASE语句来过滤掉空条目：

CREATE TABLE dfs.tmp.FOO as
select cast(columns[0] as INT) as `PRODUCT_ID`,
cast(columns[1] as INT) as `LEG_ID`,
columns[2] as `LEG_TYPE`,
CASE WHEN columns[3] = '' THEN null
  ELSE to_timestamp(columns[3], 'dd-MMM-yy HH.mm.ss.SSSSSS a') 
END as `START_DATE`
from dfs.`c:\work\prod\data\foo.csv`;

Answer 2

你也可以使用NULLIF（）函数，如下所示

CREATE TABLE dfs.tmp.FOO as
select cast(columns[0] as INT) as `PRODUCT_ID`,
cast(columns[1] as INT) as `LEG_ID`,
columns[2] as `LEG_TYPE`,
to_timestamp(NULLIF(columns[3],''), 'dd-MMM-yy HH.mm.ss.SSSSSS a') as `START_DATE`
from dfs.`c:\work\prod\data\foo.csv`;

NULLIF会将空字符串转换为null，并且转换不会失败。

使用Apache Drill从CSV创建Parquet表时出错

2 个答案: