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eval

Description

The eval command evaluates the expression and appends the result to the search result.

Syntax

eval <field>=<expression> ["," <field>=<expression> ]...

  • field: mandatory. If the field name does not exist, a new field is added. If the field name already exists, it will be overridden.
  • expression: mandatory. Any expression supported by the system.

Example 1: Create a new field

This example shows creating a new field doubleAge for each document. The new doubleAge field is the result of multiplying age by 2.

source=accounts
| eval doubleAge = age * 2
| fields age, doubleAge

Expected output:

fetched rows / total rows = 4/4
+-----+-----------+
| age | doubleAge |
|-----+-----------|
| 32  | 64        |
| 36  | 72        |
| 28  | 56        |
| 33  | 66        |
+-----+-----------+

Example 2: Override an existing field

This example shows overriding the existing age field by adding 1 to it.

source=accounts
| eval age = age + 1
| fields age

Expected output:

fetched rows / total rows = 4/4
+-----+
| age |
|-----|
| 33  |
| 37  |
| 29  |
| 34  |
+-----+

Example 3: Create a new field with field defined in eval

This example shows creating a new field ddAge using a field defined in the same eval command. The new field ddAge is the result of multiplying doubleAge by 2, where doubleAge is defined in the same eval command.

source=accounts
| eval doubleAge = age * 2, ddAge = doubleAge * 2
| fields age, doubleAge, ddAge

Expected output:

fetched rows / total rows = 4/4
+-----+-----------+-------+
| age | doubleAge | ddAge |
|-----+-----------+-------|
| 32  | 64        | 128   |
| 36  | 72        | 144   |
| 28  | 56        | 112   |
| 33  | 66        | 132   |
+-----+-----------+-------+

Example 4: String concatenation

This example shows using the + operator for string concatenation. You can concatenate string literals and field values.

source=accounts 
| eval greeting = 'Hello ' + firstname 
| fields firstname, greeting

Expected output:

fetched rows / total rows = 4/4
+-----------+---------------+
| firstname | greeting      |
|-----------+---------------|
| Amber     | Hello Amber   |
| Hattie    | Hello Hattie  |
| Nanette   | Hello Nanette |
| Dale      | Hello Dale    |
+-----------+---------------+

Example 5: Multiple string concatenation with type casting

This example shows multiple concatenations with type casting from numeric to string.

source=accounts | eval full_info = 'Name: ' + firstname + ', Age: ' + CAST(age AS STRING) | fields firstname, age, full_info

Expected output:

fetched rows / total rows = 4/4
+-----------+-----+------------------------+
| firstname | age | full_info              |
|-----------+-----+------------------------|
| Amber     | 32  | Name: Amber, Age: 32   |
| Hattie    | 36  | Name: Hattie, Age: 36  |
| Nanette   | 28  | Name: Nanette, Age: 28 |
| Dale      | 33  | Name: Dale, Age: 33    |
+-----------+-----+------------------------+

Limitations

The eval command is not rewritten to OpenSearch DSL, it is only executed on the coordination node.