hive建表后直接將數據文件拷貝到table目錄下，select * 可以查到數據，但是select count(1) 一直返回0，這個是因為hive中有個配置
hive.stats.autogather=true
Enables automated gathering of table-level statistics for newly created tables and table partitions, such as tables created with the INSERT OVERWRITE statement. The parameter does not produce column-level statistics, such as those generated by CBO. If disabled, administrators must manually generate the table-level statistics for newly generated tables and table partitions with the ANALYZE TABLE statement.
可以通過describe來查看table的統計信息
DESCRIBE EXTENDED $table_name;
有個配置控制是否使用talbe的統計信息
hive.compute.query.using.stats=true
Instructs Hive to use statistics when generating query plans
很多人建議的處理方法是
set hive.compute.query.using.stats=false;
正解應該是
ANALYZE TABLE $table_name COMPUTE STATISTICS;
ANALYZE TABLE $table_name partition(p=$1) COMPUTE STATISTICS;
即重新計算統計信息
參考：https://docs.hortonworks.com/HDPDocuments/HDP2/HDP-2.6.5/bk_hive-performance-tuning/content/ch_cost-based-optimizer.html