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Since there is no IFNULL, ISNULL, or NVL function supported on Hive, I'm having trouble converting NULL to 0. I tried COALESCE(*column name*, 0) but received the below error message:
Argument type mismatch 0: The expressions after COALESCE should all have the same type: "bigint" is expected but "int" is found
How to resolve this?
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NVL and COALESCE are used to achieve the same functionality of providing a default value in case the column returns a NULL. The differences are: NVL accepts only 2 arguments whereas COALESCE can take multiple arguments. NVL evaluates both the arguments and COALESCE stops at first occurrence of a non-Null value.
The hive nvl function is one of the same functions. We can use the nvl function as the keyword in the hive query. It will update, we need to replace the null value in the table with the specific value.
The SQL COALESCE function can be syntactically represented using the CASE expression. For example, as we know, the Coalesce function returns the first non-NULL values. SELECT COALESCE (expression1, expression2, expression3) FROM TABLENAME; The above Coalesce SQL statement can be rewritten using the CASE statement.
Hive supports bigint literal since 0.8 version. So, additional "L" is enough:
COALESCE(column, 0L) As Lamak pointed out in the comment, COALESCE(column, CAST(0 AS BIGINT)) resolves the error.
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Since 0.11 hive has a NVL function
nvl(T value, T default_value)
which says Returns default value if value is null else returns value
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From [Hive Language Manual][1]:
COALESCE (T v1, T v2, ...)
Will return the first value that is not NULL, or NULL if all values's are NULL
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-ConditionalFunctions
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If customer primary contact medium is email, if email is null then phonenumber, and if phonenumber is also null then address. It would be written using COALESCE as
coalesce(email,phonenumber,address)
while the same in hive can be achieved by chaining together nvl as
nvl(email,nvl(phonenumber,nvl(address,'n/a')))
From Language DDL & UDF of Hive
NVL(value, default value)
Returns default value if value is null else returns value
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nvl(value,defaultvalue) as Columnname
will set the missing values to defaultvalue specified
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