HogQL expressions

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

HogQL trends breakdown filter

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 (properties)
  • person properties (person.properties)
  • event
  • elements_chain (from autocapture)
  • timestamp
  • distinct_id
  • person_id
  • When joined, data warehouse source properties

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 (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)
  • NUMERIC(AKA float)

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


Expressions can use operators to filter and combine data. These include:

  • Comparison operators like =, !=, <, or >=
  • Logical operators like AND, OR, IS or NOT
  • Arithmetic operators like +, -, *, /

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:


if(cond, then, else)Checks a condition, and if true (or non-zero), returns the result of an expression
multiIf(cond1, then1, cond2, then2, ..., else)Enables chaining multiple if statements together, each with a condition and return expression
in(value, set)Checks if an array or string contains a value
match(value, regexp)Checks whether a string matches a regular expression pattern
likeChecks if a string matches a pattern that contains string(s) and symbols %, _, \ (escaped literals)


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


extract(haystack, pattern)Extracts a fragment of a string (haystack) using a regular expression (pattern) like extract(properties.$current_url, 'ref=([^&]*)')
concat(s1, s2, ...)Concatenates strings (s1, s2, etc.) listed without separator
splitByChar(separator, s)Splits string (s) into substrings separated by a specified character (separator)
replaceOne(haystack, pattern, replacement)Replace the first occurrence of matching a substring (pattern) with a replacement string (replacement). Example: replaceOne(properties.$current_url, 'https://us.posthog.com', '/')
replaceRegexpOne(haystack, pattern, replacement)Replace the first occurrence of matching a regular expression (pattern) with a replacement string (replacement)
substring(s, start)Extracts a substring from a string (s) starting at index (start)


dateDiff('unit', startdate, enddate)Returns the count in unit between startdate and enddate
toDayOfWeek, toHour, toMinuteConverts date number of day of week (1-7), hour in 24-hour time (0-23), and minute in hour (0-59) like toHour(timestamp)
now(), today(), yesterday()Returns the current time, date, or yesterday's date respectively
intervalA length of time for use in arithmetic operations with other dates and times like person.properties.trial_started + interval 30 day

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 like concat('OS Version: ', properties.$os_version).

  • Grouping or binning events based on properties using if(), multiIf() like multiIf(properties.$device_type == 'Desktop', 'Desktop', properties.$os == 'iOS', 'iOS', 'Non-iOS').

  • Accessing nested properties such as properties.$set.$geoip_city_name.

  • Filtering for events that happened in the last X minutes, hours, or days with dateDiff(), now(), and interval like dateDiff('minute', timestamp, now()) < 30.

  • Creating percentages by calculating the sum of one property over the sum of all related properties inline with sum(), /, +, and * like sumIf(1, properties.$browser = 'Chrome') / sumIf(1, properties.$browser = 'Safari' or properties.$browser = 'Chrome')

  • Binning events based on time of day, week, and month with toHour, toDayOfWeek, toStartOfWeek, toMonth like multiIf(5 >= toHour(timestamp) and toHour(timestamp) < 12, 'morning', 12 >= toHour(timestamp) and toHour(timestamp) < 17, 'afternoon', 'night')

  • Breaking down by multiple properties using concat() like concat(properties.$os_name, ' - ', properties.$os_version).

  • Matching URL patterns with like like (properties.$current_url LIKE '%/blog%')

  • Filter null property values with IS NOT NULL like person.properties.$initial_utm_source IS NOT NULL.

  • Breakdown by values in an array by using a combination of JSONExtractArrayRaw and arrayJoin like arrayJoin(JSONExtractArrayRaw(properties.$active_feature_flags ?? '[]'), ',').

  • Extracting the ID from autocaptured elements like extract(elements_chain, '[:|"]attr__id="(.*?)"').


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