# Compound Attributes

Telmai offers a **Compound Attributes** feature, which allows you to define an SQL-like expression, validate it in real-time, and inspect outputs similar to single-attribute rules.

#### Adding a Compound Attribute

1. Navigate to the **Configuration** page and select the corresponding dataset.
2. Click the "**Add Compound Attribute"** button<br>

   <figure><img src="/files/tyZDm5sNz34xOusLNU4l" alt=""><figcaption></figcaption></figure>
3. **Define the Attribute**:
   * **Attribute ID**: Name the compound attribute.
   * **Attributes to Compound**: List the attributes to be used.
   * **Expression**: Enter an SQL-like expression that defines the transformation.
4. Enter an expression. Please see below for additional information on supported functions and examples of expressions

<figure><img src="/files/xgfhVmGfbqovhivbYjeg" alt=""><figcaption></figcaption></figure>

You can validate the expression output by entering values for each corresponding attribute. When clicking on the edit field, Telmai will offer a few samples taken from the actual data to help

Once the attribute is created, you can add an expectation to it the same way you would for a standard attribute — by navigating to the **Monitoring** page for the dataset and configuring a threshold on the compound attribute.

**Important Usage Notes**:

* As the user inputs an expression, an evaluation is done to ensure a valid SQL expression
* There are some cases where the validation will pass but will fail during executions due to casting-related errors. The values should be cast appropriately to the expected type to mitigate this. The expression output must always be a string type. In case it is not, users need to cast to a string explicitly. Example:
  * If the expression has contains function; the output is boolean `contains( last_name , 'Smith')`

    The user needs to cast the value string `cast ( contains( last_name , 'Smith') as string)`
* All parameters are treated as strings. The user needs to cast the parameters to the corresponding function param type. Example:
  * If the user wants to use the date\_add function, which takes in number and a date (which is a string) The user will need to cast `my_number` first like this: `date_add('2016-07-30', cast (my_number as int))`

**Examples**

**Example 1:**

```sql
LENGTH(CONCAT_WS(\",\", firstname, lastname)) > 100
```

The output expression is boolean, so it needs to be converted to string in order to become a value of a new compound attribute:

```
CAST(LENGTH(CONCAT_WS(\",\", firstname, lastname)) > 100 as STRING)
```

**Example 2:**

```
IF( DATEDIFF(current_timestamp(), orderdate) > 10 , true , false)
```

Convert boolean to string values:

```
IF( DATEDIFF(current_timestamp(), orderdate) > 10 , 'true' , 'false' )
```

**Example 3:**

```
IF( ISNOTNULL(country) and ISNOTNULL(city) and (price <= 100)), 'true', 'false')
```

price is an attribute, so it’s value comes as a string, so it needs to be first cast to double

```
IF( ISNOTNULL(country) and ISNOTNULL(city) and (CAST(price as DOUBLE) <= 100)),'true', 'false')
```


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