【原创】大叔经验分享（33）hive select count为0

hive建表后直接将数据文件拷贝到table目录下，select * 可以查到数据，但是select count(1) 一直返回0，这个是因为hive中有个配置

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.

可以通过describe来查看table的统计信息

DESCRIBE EXTENDED $table_name;

有个配置控制是否使用talbe的统计信息

hive.compute.query.using.stats=true

Instructs Hive to use statistics when generating query plans

很多人建议的处理方法是

set hive.compute.query.using.stats=false;

正解应该是

ANALYZE TABLE $table_name COMPUTE STATISTICS;

ANALYZE TABLE $table_name partition(p=$1) COMPUTE STATISTICS;

即重新计算统计信息

参考：https://docs.hortonworks.com/HDPDocuments/HDP2/HDP-2.6.5/bk_hive-performance-tuning/content/ch_cost-based-optimizer.html