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Lambda 表达式

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Lambda 表达式

JEXL 自定义函数

函数简介

Java Expression Language (JEXL) 是一个表达式语言引擎。我们使用 JEXL 来扩展 UDF,在命令行中,通过简易的 lambda 表达式来实现 UDF。

lambda 表达式中支持的运算符详见链接 JEXL 中 lambda 表达式支持的运算符open in new window

函数名可接收的输入序列类型必要的属性参数输出序列类型功能类型
JEXLINT32 / INT64 / FLOAT / DOUBLE / TEXT / BOOLEANexpr是一个支持标准的一元或多元参数的lambda表达式,符合x -> {...}(x, y, z) -> {...}的格式,例如x -> {x * 2}, (x, y, z) -> {x + y * z}INT32 / INT64 / FLOAT / DOUBLE / TEXT / BOOLEAN返回将输入的时间序列通过lambda表达式变换的序列

使用示例

输入序列:

IoTDB> select * from root.ln.wf01.wt01;
+-----------------------------+---------------------+--------------------+-----------------------------+
|                         Time|root.ln.wf01.wt01.str|root.ln.wf01.wt01.st|root.ln.wf01.wt01.temperature|
+-----------------------------+---------------------+--------------------+-----------------------------+
|1970-01-01T08:00:00.000+08:00|                  str|                10.0|                          0.0|
|1970-01-01T08:00:00.001+08:00|                  str|                20.0|                          1.0|
|1970-01-01T08:00:00.002+08:00|                  str|                30.0|                          2.0|
|1970-01-01T08:00:00.003+08:00|                  str|                40.0|                          3.0|
|1970-01-01T08:00:00.004+08:00|                  str|                50.0|                          4.0|
|1970-01-01T08:00:00.005+08:00|                  str|                60.0|                          5.0|
|1970-01-01T08:00:00.006+08:00|                  str|                70.0|                          6.0|
|1970-01-01T08:00:00.007+08:00|                  str|                80.0|                          7.0|
|1970-01-01T08:00:00.008+08:00|                  str|                90.0|                          8.0|
|1970-01-01T08:00:00.009+08:00|                  str|               100.0|                          9.0|
|1970-01-01T08:00:00.010+08:00|                  str|               110.0|                         10.0|
+-----------------------------+---------------------+--------------------+-----------------------------+

用于查询的SQL语句:

select jexl(temperature, 'expr'='x -> {x + x}') as jexl1, jexl(temperature, 'expr'='x -> {x * 3}') as jexl2, jexl(temperature, 'expr'='x -> {x * x}') as jexl3, jexl(temperature, 'expr'='x -> {multiply(x, 100)}') as jexl4, jexl(temperature, st, 'expr'='(x, y) -> {x + y}') as jexl5, jexl(temperature, st, str, 'expr'='(x, y, z) -> {x + y + z}') as jexl6 from root.ln.wf01.wt01;

输出序列:

+-----------------------------+-----+-----+-----+------+-----+--------+
|                         Time|jexl1|jexl2|jexl3| jexl4|jexl5|   jexl6|
+-----------------------------+-----+-----+-----+------+-----+--------+
|1970-01-01T08:00:00.000+08:00|  0.0|  0.0|  0.0|   0.0| 10.0| 10.0str|
|1970-01-01T08:00:00.001+08:00|  2.0|  3.0|  1.0| 100.0| 21.0| 21.0str|
|1970-01-01T08:00:00.002+08:00|  4.0|  6.0|  4.0| 200.0| 32.0| 32.0str|
|1970-01-01T08:00:00.003+08:00|  6.0|  9.0|  9.0| 300.0| 43.0| 43.0str|
|1970-01-01T08:00:00.004+08:00|  8.0| 12.0| 16.0| 400.0| 54.0| 54.0str|
|1970-01-01T08:00:00.005+08:00| 10.0| 15.0| 25.0| 500.0| 65.0| 65.0str|
|1970-01-01T08:00:00.006+08:00| 12.0| 18.0| 36.0| 600.0| 76.0| 76.0str|
|1970-01-01T08:00:00.007+08:00| 14.0| 21.0| 49.0| 700.0| 87.0| 87.0str|
|1970-01-01T08:00:00.008+08:00| 16.0| 24.0| 64.0| 800.0| 98.0| 98.0str|
|1970-01-01T08:00:00.009+08:00| 18.0| 27.0| 81.0| 900.0|109.0|109.0str|
|1970-01-01T08:00:00.010+08:00| 20.0| 30.0|100.0|1000.0|120.0|120.0str|
+-----------------------------+-----+-----+-----+------+-----+--------+
Total line number = 11
It costs 0.118s

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