diff --git a/site/_docs/reference.md b/site/_docs/reference.md
index 22412aca7ae..376fed26f70 100644
--- a/site/_docs/reference.md
+++ b/site/_docs/reference.md
@@ -1503,6 +1503,7 @@ Not implemented:
 | MINUTE(date)              | Equivalent to `EXTRACT(MINUTE FROM date)`. Returns an integer between 0 and 59.
 | SECOND(date)              | Equivalent to `EXTRACT(SECOND FROM date)`. Returns an integer between 0 and 59.
 | TIMESTAMPADD(timeUnit, integer, datetime) | Returns *datetime* with an interval of (signed) *integer* *timeUnit*s added. Equivalent to `datetime + INTERVAL 'integer' timeUnit`
+| TIMESTAMPDIFF(timeUnit, datetime, datetime2) | Returns the (signed) number of *timeUnit* intervals between *datetime* and *datetime2*. Equivalent to `(datetime2 - datetime) timeUnit`
 | LAST_DAY(date)            | Returns the date of the last day of the month in a value of datatype DATE; For example, it returns DATE'2020-02-29' for both DATE'2020-02-10' and TIMESTAMP'2020-02-10 10:10:10'
 
 Calls to niladic functions such as `CURRENT_DATE` do not accept parentheses in