I am having trouble trying to define map type in hive. According to Hive Manual there definitely is a map type, unfortunately there aren't any examples on how to use it. :-(
Suppose, I have a table (users) with following columns:
Name Ph CategoryName
This "CategoryName" column has specific set of values. Now I want to create a hashtable that maps CategoryName to CategoryID. I tried doing:
set hivevar:nameToID=map('A',1,'B',2);
I have 2 questions:
When I do set hivevar:${nameToID['A']}
I thought that it would print out value as 1. But I get
"${hivevar:nameToID['A']} is undefined"
I am not sure how can I say something like, select name, ph, ${nameToID[CategoryName]} from users
map: It is an unordered collection of key-value pairs. Keys must be of primitive types. Values can be of any type. struct: It is a collection of elements of different types. Examples: complex datatypes.
By using this command below one can change the column data type: ALTER TABLE table_name CHANGE column_name column_name new_datatype; I hope this works.
STRUCT : The struct data type in Hive is analogous to the STRUCT in C programming language. It is a record type that holds a set of named fields that can be of any primitive data types. Fields in the STRUCT type are accessed using the DOT ( . ) notation.
String Types It contains two data types: VARCHAR and CHAR. Hive follows C-types escape characters.
Let's assume you have the following table:
describe test;
name string
ph string
category map<string,int>
select * from test;
name ph category
Name1 ph1 {"type":1000,"color":200,"shape":610}
Name2 ph2 {"type":2000,"color":200,"shape":150}
Name3 ph3 {"type":3000,"color":700,"shape":167}
Accessing the map column :
select ph, category["type"], category["color"] from test;
ph1 1000 200
ph2 2000 200
ph3 3000 700
An equivalent using a Hive variable:
set hivevar:nameToID=
map("t", category["type"], "c", category["color"], "s", category["shape"]);
select ph, ${nameToID}["t"], ${nameToID}["c"] from test;
ph1 1000 200
ph2 2000 200
ph3 3000 700
This works on Hive 0.9.0
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