HogQL expressions

HogQL expressions enable you to directly access, modify, and aggregate data in many places in PostHog including:

Filters
Trends series
Breakdowns
Funnel aggregations
User paths
Session replays
Dashboards
The activity tab

Tip: If you're having trouble getting results from your expression, try debugging by using a different visualization (trends table often works best as it shows all values returned) or breaking down your expression into pieces and testing each one.

Accessible data

HogQL expressions can access data like:

event properties
person properties
event
elements_chain (from autocapture)
timestamp
distinct_id
person_id

Properties can be accessed with dot notation like person.properties.$initial_browser which also works for nested or JSON properties. They can also be accessed with bracket notation like properties['$feature/cool-flag'].

Note: PostHog's properties always include $ as a prefix, while custom properties do not (unless you add it).

Property identifiers must be known at query time. For dynamic access, use the JSON manipulation functions from below on the properties field directly.

Types

Types (and names) for the accessible data can be found in the database and properties tabs in data management. They include:

STRING (default)
JSON (accessible with dot or bracket notation)
DATETIME(in ISO-8601, read more in our data docs)
INTEGER
NUMERIC(AKA float)
BOOLEAN

Types can be converted using functions like toString, toDate, toFloat, JSONExtractString, JSONExtractInt, and more.

Functions and aggregations

You can filter, modify, or aggregate accessed data with supported ClickHouse functions like dateDiff() and concat() and aggregations like sumIf() and count().

Here are some of the most common and useful ones:

Comparisons

if: Checks a condition, and if true (or non-zero), and then returns the result of an expression.
multiIf: Enables chaining multiple if statements together, each with a condition and return expression.
in: Checks if an array or string contains a value.
match: Checks whether a string matches a regular expression pattern.
like: Checks if string matches pattern that contain string(s) and symbols % (arbitrary number of arbitrary characters), _ (single arbitrary character), \ (escaped literals).

Aggregations

count: Counts the values. If you want a condition, use sumIf.
count(distinct): Counts the number of uniqExact values.
uniq: Calculates the approximate number of different values (uniqExact is slower but exact).
uniqExact: Calculates the exact number of different argument values (uniq is faster and you should use it if a close approximation is good enough).
sum: Calculates the total (sum) numeric value.
sumIf: Calculates the total (sum) numeric value for values meeting a condition.
avg: Calculates the average numeric value.
median: Computes an approximate middle (50%) value for a numeric data sequence.

Strings

extract: Extracts a fragment of a string using a regular expression.
concat: Concatenates strings listed without separator.
splitByChar: Splits string into substrings separated by a specified character.
replaceOne, replaceRegexpOne: Replace the first occurrence of matching a substring or regular expression pattern respectively with a replacement string.

Dates

dateDiff('unit', startdate, enddate): Returns the count in unit between startdate and enddate.
toDayOfWeek, toHour, toMinute: Converts date number of day of week (1-7), hour in 24-hour time (0-23), and minute in hour (0-59).
now(), today(), yesterday(): Returns the current time, date, or yesterday’s date respectively.
interval: A length of time for use in arithmetic operations with other dates and times.

Use cases

Checking if a property or autocapture element chain contains a specific value or any of an array of values using in or match.
Modifying the display string in the visualization by extracting or concatenating properties using concat(), +, extract(), or replaceOne.
Grouping or binning events based on properties using if(), multiIf().
Accessing nested properties such as properties.$set.$geoip_city_name.
Filtering for events that happened in the last X minutes or hours with dateDiff(), now(), and interval.
Creating percentages by calculating the sum of one property over the sum of all related properties with sum(), /, +, and *.
Getting unique values with uniq().
Binning events based on time of day, week, and month with toHour, toDayOfWeek, toStartOfWeek, toMonth.
Breaking down by multiple properties using concat().