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# Lambda Expression

## JEXL Function

Java Expression Language (JEXL) is an expression language engine. We use JEXL to extend UDFs, which are implemented on the command line with simple lambda expressions. See the link for [operators supported in jexl lambda expressions](https://commons.apache.org/proper/commons-jexl/apidocs/org/apache/commons/jexl3/package-summary.html#customization).

| Function Name | Allowed Input Series Data Types | Required Attributes                           | Output Series Data Type | Series Data Type  Description                 |
|----------|--------------------------------|---------------------------------------|------------|--------------------------------------------------|
| JEXL   | INT32 / INT64 / FLOAT / DOUBLE / TEXT / BOOLEAN | `expr` is a lambda expression that supports standard one or multi arguments in the form `x -> {...}` or `(x, y, z) -> {...}`, e.g. ` x -> {x * 2}`, `(x, y, z) -> {x + y * z}` | INT32 / INT64 / FLOAT / DOUBLE / TEXT / BOOLEAN | Returns the input time series transformed by a lambda expression |

#### Demonstrate
Example data: `root.ln.wf01.wt01.temperature`, `root.ln.wf01.wt01.st`, `root.ln.wf01.wt01.str` a total of `11` data.

```
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|
+-----------------------------+---------------------+--------------------+-----------------------------+
```
Sql:
```sql
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;```
```

Result:
```
+-----------------------------+-----+-----+-----+------+-----+--------+
|                         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
```