Question

我在Ubuntu 14.0上运行Apache Hadoop 2.6.0，我在Hive 0.13.0中创建了一个表：

CREATE TABLE IF NOT EXISTS recipes_hive.cuisine (
ID INT COMMENT 'Cuisine ID.', 
name STRING COMMENT 'Cusine name - primary key.', 
area STRING COMMENT 'Name of the area of origin - foreign key.', 
scope STRING COMMENT 'Either country or area.') 
COMMENT 'Table containing cuisines data.'
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE;

我用声明填充数据：

LOAD DATA LOCAL INPATH 'path_to_file/CUISINE.csv'
OVERWRITE INTO TABLE recipes_hive.cuisine;

我的数据库有几个这样的表都创建并填充相同的过程。运行简单查询时：

SELECT * FROM cuisine

甚至WHERE子句中的某些条件我得到了预期的结果，但运行更复杂的查询我得到了蹲下。例如：

SELECT cuisine.name, SUM(IF (ingredient.category = "fruit",1,2))/count(*) AS      PERC 
FROM cuisine JOIN recipe ON recipe.cuisine = cuisine.name JOIN part_of ON part_of.id_recipe = recipe.id JOIN ingredient ON ingredient.name = part_of.ingredient 
GROUP BY cuisine.name 
ORDER BY PERC DESC

，或：

SELECT ingredient.id, ingredient.name 
FROM cuisine JOIN recipe ON recipe.cuisine = cuisine.name JOIN part_of ON part_of.id_recipe = recipe.id JOIN ingredient ON ingredient.name = part_of.ingredient 
WHERE ingredient.id IN (
SELECT ingredient.id 
FROM cuisine c JOIN recipe ON recipe.cuisine = c.name JOIN part_of ON part_of.id_recipe = recipe.id JOIN ingredient ON ingredient.name = part_of.ingredient 
WHERE c.name = "Pakistan") AND cuisine.name = "Bangladesh"

第一个示例计算一些百分比，第二个示例检查相互元素。

正确调用MapReduce和Hadoop，它们不会返回任何错误。输出结束于：

Execution completed successfully
MapredLocal task succeeded
OK
Time taken: 122.119 seconds

我检查了网络，人们和我一样有类似的问题。我查了一下：

Hive Table returning empty result set on all queries

Simple Hive query is empty

但未能解决我的问题。这些数据实际上是在HDFS中，如前所述，它可用于简单查询。

因此，我的Hive实例出现问题或者我的查询编写错误。

非常感谢任何帮助。最好的问候。

Answer 1

您确定结果联接是否为非空。因为，您已经实现了内连接，即使一个表缺少记录，整个结果集也是0.尝试使用＆＃34; IS NULL添加左连接＆＃34;验证所有表对结果集的贡献。如果所有子表在连接后的各自列中都具有非空值，则查询是好的。

Answer 2

如果我们有包含ID = {1,2,3}的Cuisine表和包含ID = {5,6,7}的Recipe表，那么即使这些表非空，我们仍然不会返回任何行INNER JOIN Cuisine.ID = Recipe.ID（因为2个表中的ID不同）请你检查一下是否有这种情况。

SELECT count(1)
FROM cuisine c JOIN recipe ON recipe.cuisine = c.name WHERE c.name = "Pakistan";

--- must return > 0 

select count(1) from recipe as recipe
JOIN part_of ON part_of.id_recipe = recipe.id ;

--- must return > 0 

select count(1) from part_of as part_of
JOIN ingredient ON ingredient.name = part_of.ingredient ;

--- must return > 0

因此，当所有count（*）都不为零时，内部查询返回一行。现在测试外部选择：

SELECT ingredient.id, ingredient.name 
FROM cuisine JOIN recipe ON recipe.cuisine = cuisine.name JOIN part_of ON part_of.id_recipe = recipe.id JOIN ingredient ON ingredient.name = part_of.ingredient 
WHERE ingredient.id = <inner query result> and cuisine.name = "Bangladesh";

HiveQL查询不返回任何结果且没有错误

2 个答案: