HogQL expressions

HogQL expressions enable you to directly access, modify, and aggregate data in PostHog using SQL. You can use them nearly everywhere where event filters exist, including:

• Dashboards
• Data series
• Breakdowns
• Funnels
• The activity tab

HogQL expressions can access data like:

• event properties
• person properties
• event
• elements_chain
• timestamp
• distinct_id
• person_id

They then use SQL functions to access, filter, modify, or aggregate the data. A full list of SQL functions are found in our supported ClickHouse functions and supported aggregations docs.

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.

Useful functions

To help you get the most out of HogQL expressions, here are some of the most popular functions.

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 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.