edgar2020 commented on code in PR #16878:
URL: https://github.com/apache/druid/pull/16878#discussion_r1715623788
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docs/querying/sql-functions.md:
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@@ -1077,11 +1077,42 @@ Calculates the base-10 of the numeric expression.
## LOOKUP
-`LOOKUP(<CHARACTER>, <CHARACTER>[, <CHARACTER>])`
+Look up `expr` in a registered [query-time lookup table](lookups.md) named
`lookupName`. Returns `replaceMissingValueWith`, which defaults to `null`, when
the `expr` is null or when the lookup does not contain a value for `expr`.
-**Function type:** [Scalar, string](sql-scalar.md#string-functions)
+* **Syntax:** `LOOKUP(expr, lookupName[, replaceMissingValueWith])`
+* **Function type:** Scalar, string
+
+<details><summary>Example</summary>
+
+The following example uses a map lookup table, named `acronym_to_name` made
with the following key-value pairs:
+
+```json
+{
+ “SJU”: Luis Munoz Marin International Airport”,
+ “IAD”: “Dulles International AirportDulles International Airport”
+}
+```
+
+The example uses `acronym_to_name` to map the `Origin` column from the
`flight-carriers` datasource to its full airport name. Returns `NaN` if no
matching value exist in the lookup table.
Review Comment:
In retrospect probably non, I could change it to "NULL" or "key not found"
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