Spark SQL----内置函数Conversion Functions& Conditional Functions
- Conversion Functions
例子：
-- cast
SELECT cast('10' as int);
+---------------+
|CAST(10 AS INT)|
+---------------+
| 10|
+---------------+
- Conditional Functions
例子：
-- coalesce
SELECT coalesce(NULL, 1, NULL);
+-----------------------+
|coalesce(NULL, 1, NULL)|
+-----------------------+
| 1|
+-----------------------+-- if
SELECT if(1 < 2, 'a', 'b');
+-------------------+
|(IF((1 < 2), a, b))|
+-------------------+
| a|
+-------------------+-- ifnull
SELECT ifnull(NULL, array('2'));
+----------------------+
|ifnull(NULL, array(2))|
+----------------------+
| [2]|
+----------------------+-- nanvl
SELECT nanvl(cast('NaN' as double), 123);
+-------------------------------+
|nanvl(CAST(NaN AS DOUBLE), 123)|
+-------------------------------+
| 123.0|
+-------------------------------+-- nullif
SELECT nullif(2, 2);
+------------+
|nullif(2, 2)|
+------------+
| NULL|
+------------+-- nvl
SELECT nvl(NULL, array('2'));
+-------------------+
|nvl(NULL, array(2))|
+-------------------+
| [2]|
+-------------------+-- nvl2
SELECT nvl2(NULL, 2, 1);
+----------------+
|nvl2(NULL, 2, 1)|
+----------------+
| 1|
+----------------+-- when
SELECT CASE WHEN 1 > 0 THEN 1 WHEN 2 > 0 THEN 2.0 ELSE 1.2 END;
+-----------------------------------------------------------+
|CASE WHEN (1 > 0) THEN 1 WHEN (2 > 0) THEN 2.0 ELSE 1.2 END|
+-----------------------------------------------------------+
| 1.0|
+-----------------------------------------------------------+SELECT CASE WHEN 1 < 0 THEN 1 WHEN 2 > 0 THEN 2.0 ELSE 1.2 END;
+-----------------------------------------------------------+
|CASE WHEN (1 < 0) THEN 1 WHEN (2 > 0) THEN 2.0 ELSE 1.2 END|
+-----------------------------------------------------------+
| 2.0|
+-----------------------------------------------------------+SELECT CASE WHEN 1 < 0 THEN 1 WHEN 2 < 0 THEN 2.0 END;
+--------------------------------------------------+
|CASE WHEN (1 < 0) THEN 1 WHEN (2 < 0) THEN 2.0 END|
+--------------------------------------------------+
| NULL|
+--------------------------------------------------+
