无法推断 COUNT 函数

Posted 2023-04-18

【中文标题】无法推断 COUNT 函数

【英文标题】：Could not infer COUNT function

【发布时间】：2012-03-22 16:19:18

【问题描述】：

我正在尝试编写一个猪拉丁语脚本来提取我已过滤的数据集的计数。

这是目前为止的脚本：

/* scans by title */

scans           = LOAD '/hive/scans/*' USING PigStorage(',') AS (thetime:long,product_id:long,lat:double,lon:double,user:chararray,category:chararray,title:chararray);
productscans    = FILTER scans BY (title MATCHES 'proactiv');
scancount       = FOREACH productscans GENERATE COUNT($0);
DUMP scancount;

由于某种原因，我得到了错误：

无法将 org.apache.pig.builtin.COUNT 的匹配函数推断为多个匹配或都不匹配。请使用显式强制转换。

我在这里做错了什么？我假设它与我传入的字段类型有关，但我似乎无法解决这个问题。

TIA, 杰森

【参考方案1】：

这是你要找的东西吗（把所有东西都放在一个袋子里，然后数数）：

scans           = LOAD '/hive/scans/*' USING PigStorage(',') AS (thetime:long,product_id:long,lat:double,lon:double,user:chararray,category:chararray,title:chararray);
productscans    = FILTER scans BY (title MATCHES 'proactiv');
grouped         = GROUP productscans ALL;
count           = FOREACH grouped GENERATE COUNT(productscans);
dump count;

【讨论】：

就是这样（减去“FOREACH g”应该是“FOREACH 分组”） - 谢谢克里斯！

【参考方案2】：

COUNT 对于全局计数需要前面的 GROUP ALL 语句，对于组计数需要一个 GROUP BY 语句。

您可以使用以下任何一种：

scans           = LOAD '/hive/scans/*' USING PigStorage(',') AS (thetime:long,product_id:long,lat:double,lon:double,user:chararray,category:chararray,title:chararray);
productscans    = FILTER scans BY (title MATCHES 'proactiv');
grouped         = GROUP productscans ALL;
count           = FOREACH grouped GENERATE COUNT(productscans);
DUMP scancount;

或者

scans           = LOAD '/hive/scans/*' USING PigStorage(',') AS (thetime:long,product_id:long,lat:double,lon:double,user:chararray,category:chararray,title:chararray);
productscans    = FILTER scans BY (title MATCHES 'proactiv');
grouped         = GROUP productscans ALL;
count           = FOREACH grouped GENERATE COUNT($1);
DUMP scancount;

【参考方案3】：

也许

/* scans by title */

scans           = LOAD '/hive/scans/*' USING PigStorage(',') AS (thetime:long,product_id:long,lat:double,lon:double,user:chararray,category:chararray,title:chararray);
productscans    = FILTER scans BY (title MATCHES 'proactiv');
scancount       = FOREACH productscans GENERATE COUNT(productscans);
DUMP scancount;

【讨论】：

感谢 Jake - 不幸的是，没有运气。这给了我：Invalid scalar projection: productscans : A column needs to be projected from a relation for it to be used as a scalar