Start a PPL query with a `search` command to reference a table to search from. You can have the commands that follow in any order.
In the following example, the `search` command refers to an `accounts` index as the source, then uses `fields` and `where` commands for the conditions:
```sql
search source=accounts
| where age > 18
| fields firstname, lastname
```
In the below examples, we represent required arguments in angle brackets `< >` and optional arguments in square brackets `[ ]`.
{: .note }
## search
Use the `search` command to retrieve a document from an index. You can only use the `search` command as the first command in the PPL query.
### Syntax
```sql
search source=<index> [boolean-expression]
```
Field | Description | Required
:--- | :--- |:---
`search` | Specify search keywords. | Yes
`index` | Specify which index to query from. | No
`bool-expression` | Specify an expression that evaluates to a boolean value. | No
*Example 1*: Get all documents
To get all documents from the `accounts` index:
```sql
search source=accounts;
```
| account_number | firstname | address | balance | gender | city | employer | state | age | email | lastname |
`int` | Retain the specified number of duplicate events for each combination. The number must be greater than 0. If you do not specify a number, only the first occurring event is kept and all other duplicates are removed from the results. | `string` | No | 1
`keepempty` | If true, keep the document if any field in the field list has a null value or a field missing. | `nested list of objects` | No | False
Use the `stats` command to aggregate from search results.
The following table lists the aggregation functions and also indicates how each one handles null or missing values:
Function | NULL | MISSING
:--- | :--- |:---
`COUNT` | Not counted | Not counted
`SUM` | Ignore | Ignore
`AVG` | Ignore | Ignore
`MAX` | Ignore | Ignore
`MIN` | Ignore | Ignore
### Syntax
```
stats <aggregation>... [by-clause]...
```
Field | Description | Required | Default
:--- | :--- |:---
`aggregation` | Specify a statistical aggregation function. The argument of this function must be a field. | Yes | 1000
`by-clause` | Specify one or more fields to group the results by. If not specified, the `stats` command returns only one row, which is the aggregation over the entire result set. | No | -
*Example 1*: Calculate the average value of a field
To calculate the average `age` of all documents:
```sql
search source=accounts | stats avg(age);
```
| avg(age)
:--- |
| 32.25
*Example 2*: Calculate the average value of a field by group
To calculate the average age grouped by gender:
```sql
search source=accounts | stats avg(age) by gender;
```
| gender | avg(age)
:--- | :--- |
| F | 28.0
| M | 33.666666666666664
*Example 3*: Calculate the average and sum of a field by group
To calculate the average and sum of age grouped by gender:
```sql
search source=accounts | stats avg(age), sum(age) by gender;
```
| gender | avg(age) | sum(age)
:--- | :--- |
| F | 28 | 28
| M | 33.666666666666664 | 101
*Example 4*: Calculate the maximum value of a field
To calculate the maximum age:
```sql
search source=accounts | stats max(age);
```
| max(age)
:--- |
| 36
*Example 5*: Calculate the maximum and minimum value of a field by group
To calculate the maximum and minimum age values grouped by gender:
```sql
search source=accounts | stats max(age), min(age) by gender;
```
| gender | min(age) | max(age)
:--- | :--- | :--- |
| F | 28 | 28
| M | 32 | 36
## where
Use the `where` command with a bool expression to filter the search result. The `where` command only returns the result when the bool expression evaluates to true.
### Syntax
```sql
where <boolean-expression>
```
Field | Description | Required
:--- | :--- |:---
`bool-expression` | An expression that evaluates to a boolean value. | No
*Example 1*: Filter result set with a condition
To get all documents from the `accounts` index where `account_number` is 1 or gender is `F`:
