问题
What is the difference between explode and explode_outer? The documentation for both functions is the same and also the examples for both functions are identical:
SELECT explode(array(10, 20));
10
20
and
SELECT explode_outer(array(10, 20));
10
20
The Spark source suggests that there is a difference between the two functions
expression[Explode]("explode"),
expressionGeneratorOuter[Explode]("explode_outer")
but what is the effect of expressionGeneratorOuter compared to expression?
回答1:
explode creates a row for each element in the array or map column by ignoring null or empty values in array whereas explode_outer returns all values in array or map including null or empty.
For example, for the following dataframe-
id | name | likes
_______________________________
1 | Luke | [baseball, soccer]
2 | Lucy | null
explode gives the following output-
id | name | likes
_______________________________
1 | Luke | baseball
1 | Luke | soccer
Whereas explode_outer gives the following output-
id | name | likes
_______________________________
1 | Luke | baseball
1 | Luke | soccer
2 | Lucy | null
SELECT explode(col1) from values (array(10,20)), (null)
returns
+---+
|col|
+---+
| 10|
| 20|
+---+
while
SELECT explode_outer(col1) from values (array(10,20)), (null)
returns
+----+
| col|
+----+
| 10|
| 20|
|null|
+----+
来源：https://stackoverflow.com/questions/64377894/difference-between-explode-and-explode-outer