如何在Apache Drill中查看Map数据类型的大小？

Got it, let's solve this issue. When your Hive array field cdrlist gets converted to a Map in Apache Drill, the size() or REPEATED_COUNT() functions don't work as expected—but there are straightforward workarounds using Drill's built-in functions:

• Use MAP_KEYS() combined with ARRAY_LENGTH()
  The MAP_KEYS() function extracts all keys from your Map into an array, and ARRAY_LENGTH() gives you the length of that array (which equals the number of key-value pairs in the Map). Here's the query:

  SELECT ARRAY_LENGTH(MAP_KEYS(cdrlist)) AS map_size FROM somet_table;
  

• Alternative: MAP_VALUES() + ARRAY_LENGTH()
  This works the same way, but extracts the values of the Map into an array instead. Since every key has a corresponding value, the length will be identical:

  SELECT ARRAY_LENGTH(MAP_VALUES(cdrlist)) AS map_size FROM somet_table;
  

Both methods will reliably return the total number of entries in your Map field. Even if your Map contains NULL values, MAP_VALUES() will retain them, so the length calculation stays accurate.

内容的提问来源于stack exchange，提问作者Srihari Karanth