> For the complete documentation index, see [llms.txt](https://cortex-docs.paloaltonetworks.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cortex-docs.paloaltonetworks.com/cortex-xdr-3.x/cortex-xdr-3.x-documentation/cortex-xdr-xql/functions/lag.md).

# lag

**Syntax**

```programlisting
windowcomp lag(<field>) [by <field> [,<field>,...]] sort [asc|desc] <field1> [, [asc|desc] <field2>,...] [as <alias>]
```

**Description**

The `lag()` function is a navigation function that is used in combination with a [windowcomp](/cortex-xdr-3.x/cortex-xdr-3.x-documentation/cortex-xdr-xql/stages/windowcomp.md) stage. This function is used to return a single value of a field on a preceding row for each row in the group of rows using a combination of the `by` clause and `sort` (mandatory).

**Example**

Retrieve for each event the timestamp of the previous successful login since the last one.

```programlisting
preset = authentication_story
| filter auth_identity not in (null, """""") and auth_outcome = """SUCCESS"""
| alter ep = to_epoch(_time)
| limit 100
| windowcomp lag(_time) by auth_identity sort asc ep as previous_login
```


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