使用Presto从CSV文件创建Hive表失败

Question

我想使用Presto创建一个Hive表，其中的数据存储在S3上的csv文件中。

我已经将该文件上传到S3，并且确信Presto能够连接到Bucket。

现在，当我给出“create table”命令时，在查询表时，我得到所有值（行）为NULL的结果。

我尝试查看类似的问题，但是结果发现Presto在Stackoverflow上不那么有名。

文件中的一些行：

PassengerId,Survived,Pclass,Name,Sex,Age,SibSp,Parch,Ticket,Fare,Cabin,Embarked
1,0,3,"Braund, Mr. Owen Harris",male,22,1,0,A/5 21171,7.25,,S
2,1,1,"Cumings, Mrs. John Bradley (Florence Briggs Thayer)",female,38,1,0,PC 17599,71.2833,C85,C
3,1,3,"Heikkinen, Miss. Laina",female,26,0,0,STON/O2. 3101282,7.925,,S
4,1,1,"Futrelle, Mrs. Jacques Heath (Lily May Peel)",female,35,1,0,113803,53.1,C123,S
5,0,3,"Allen, Mr. William Henry",male,35,0,0,373450,8.05,,S
6,0,3,"Moran, Mr. James",male,,0,0,330877,8.4583,,Q
7,0,1,"McCarthy, Mr. Timothy J",male,54,0,0,17463,51.8625,E46,S
8,0,3,"Palsson, Master. Gosta Leonard",male,2,3,1,349909,21.075,,S
9,1,3,"Johnson, Mrs. Oscar W (Elisabeth Vilhelmina Berg)",female,27,0,2,347742,11.1333,,S
10,1,2,"Nasser, Mrs. Nicholas (Adele Achem)",female,14,1,0,237736,30.0708,,C
11,1,3,"Sandstrom, Miss. Marguerite Rut",female,4,1,1,PP 9549,16.7,G6,S
12,1,1,"Bonnell, Miss. Elizabeth",female,58,0,0,113783,26.55,C103,S
13,0,3,"Saundercock, Mr. William Henry",male,20,0,0,A/5. 2151,8.05,,S
14,0,3,"Andersson, Mr. Anders Johan",male,39,1,5,347082,31.275,,S
15,0,3,"Vestrom, Miss. Hulda Amanda Adolfina",female,14,0,0,350406,7.8542,,S
16,1,2,"Hewlett, Mrs. (Mary D Kingcome) ",female,55,0,0,248706,16,,S
17,0,3,"Rice, Master. Eugene",male,2,4,1,382652,29.125,,Q
18,1,2,"Williams, Mr. Charles Eugene",male,,0,0,244373,13,,S
19,0,3,"Vander Planke, Mrs. Julius (Emelia Maria Vandemoortele)",female,31,1,0,345763,18,,S
20,1,3,"Masselmani, Mrs. Fatima",female,,0,0,2649,7.225,,C

我的csv文件在这里，请从这里获取train.csv。因此，我的presto命令是：

create table testing_nan_4 ( PassengerId integer, Survived integer, Pclass integer, Name varchar, Sex varchar, Age integer, SibSp integer, Parch integer, Ticket integer, Fare double, Cabin varchar, Embarked varchar ) with ( external_location = 's3://my_bucket/titanic_train/', format = 'textfile' );

结果如下：

 passengerid | survived | pclass | name | sex  | age  | sibsp | parch | ticket | fare | cabin | embarked
-------------+----------+--------+------+------+------+-------+-------+--------+------+-------+----------
 NULL        | NULL     | NULL   | NULL | NULL | NULL | NULL  | NULL  | NULL   | NULL | NULL  | NULL
 NULL        | NULL     | NULL   | NULL | NULL | NULL | NULL  | NULL  | NULL   | NULL | NULL  | NULL
 NULL        | NULL     | NULL   | NULL | NULL | NULL | NULL  | NULL  | NULL   | NULL | NULL  | NULL
 NULL        | NULL     | NULL   | NULL | NULL | NULL | NULL  | NULL  | NULL   | NULL | NULL  | NULL
 NULL        | NULL     | NULL   | NULL | NULL | NULL | NULL  | NULL  | NULL   | NULL | NULL  | NULL
 NULL        | NULL     | NULL   | NULL | NULL | NULL | NULL  | NULL  | NULL   | NULL | NULL  | NULL
 NULL        | NULL     | NULL   | NULL | NULL | NULL | NULL  | NULL  | NULL   | NULL | NULL  | NULL
 NULL        | NULL     | NULL   | NULL | NULL | NULL | NULL  | NULL  | NULL   | NULL | NULL  | NULL

期望得到的是实际数据。

- Aviral Srivastava

Answer 1

CSV Hive 存储格式目前在 Starburst Presto 中得到支持，详情请参见：https://docs.starburstdata.com/latest/release/release-302-e.html?highlight=csv

还有正在进行的工作，让它在 PrestoSQL 中发挥作用，请参见：https://github.com/prestosql/presto/pull/920

然后您可以使用以下命令在 Presto Hive 连接器中查询此类表格：

CREATE TABLE hive.default.csv_table_with_custom_parameters (
    c_bigint varchar,
    c_varchar varchar)
WITH (
    csv_escape = '',
    csv_quote = '',  
    csv_separator = U&'\0001', -- to pass unicode character
    external_location = 'hdfs://hadoop/datacsv_table_with_custom_parameters',
    format = 'CSV')

在您的情况下，应该是这样的：

CREATE TABLE hive.default.csv_table_with_custom_parameters (
       PassengerId int, Survived int, Pclass int, Name string, Sex string, Age int, SibSp int, Parch int, Ticket int, Fare double, Cabin string, Embarked string)
WITH (
    csv_escape = '\',
    csv_quote = '"',  
    csv_separator = ',',
    external_location = 's3://my_bucket/titanic_train/',
    format = 'CSV')

请注意，仅支持单个字符值用于csv_escape、csv_quote和csv_separator表属性。

此外，在Presto中，"skip.header.line.count"="1"对于CSV表还没有等价的语法。因此，建议您从数据文件中删除标题。

- kokosing

---

"skip.header.line.count"="1" 的等效选项是 skip_header_line_count = 1。 - shawnzhu

Answer 2

目前，在文本文件格式中，您必须提供一个以0x1分隔符（'\u0001'）的文件才能被正确读取。问题在于Presto在此处不支持自定义分隔符。

建议在此处使用Hive DDL，并在Presto中轻松读取。

以下是Hive查询：

最初的回答：https://github.com/prestodb/presto/issues/10905

CREATE EXTERNAL TABLE mytable ( 
   PassengerId int, Survived int, Pclass int, Name string, Sex string, Age int, SibSp int, Parch int, Ticket int, Fare double, Cabin string, Embarked string 
)

ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.OpenCSVSerde'
WITH SERDEPROPERTIES (
  'separatorChar' = ',',
  'quoteChar' = '\"',
  'escapeChar' = '\\'
)
STORED AS TEXTFILE
LOCATION 's3://bucket-path/csv_data/'
TBLPROPERTIES (
  "skip.header.line.count"="1")

- Ashish