[Docs] Batch09: only `lookup` (#16878)

* [Docs] Batch09: only `lookup`

* slight changes

* Apply suggestions from code review

Co-authored-by: Katya Macedo  <38017980+ektravel@users.noreply.github.com>

* applying suggestiontions

* Apply suggestions from code review

Co-authored-by: Victoria Lim <vtlim@users.noreply.github.com>

* otherwise null -> otherwise returns null

* updating definition in sql-scalar.md

* Apply suggestions from code review

Co-authored-by: Charles Smith <techdocsmith@gmail.com>

* hoping to re-run web checks

* change replaceMissingValueWith -> defaultValue

* Update docs/querying/sql-scalar.md

Co-authored-by: Katya Macedo  <38017980+ektravel@users.noreply.github.com>

* acronym_to_name -> airportcode_to_name

* shortens `airportcode_to_name` to `code_to_name`

---------

Co-authored-by: Katya Macedo <38017980+ektravel@users.noreply.github.com>
Co-authored-by: Victoria Lim <vtlim@users.noreply.github.com>
Co-authored-by: Charles Smith <techdocsmith@gmail.com>

docs/querying/sql-functions.md

@@ -1546,11 +1546,42 @@ Returns the following:
 
 ## LOOKUP
 
-`LOOKUP(<CHARACTER>, <CHARACTER>[, <CHARACTER>])`
+Searches for `expr` in a registered [query-time lookup table](lookups.md) named `lookupName` and returns the mapped value. If `expr` is null or not contained in the lookup, returns `defaultValue` if supplied, otherwise returns null.
 
-**Function type:** [Scalar, string](sql-scalar.md#string-functions)
+* **Syntax:** `LOOKUP(expr, lookupName[, defaultValue])`
+* **Function type:** Scalar, string
 
-Looks up the expression in a registered query-time lookup table.
+<details><summary>Example</summary>
+
+The following example uses a `map` type lookup table named `code_to_name`, which contains the following key-value pairs:
+
+```json
+{
+  "SJU": "Luis Munoz Marin International Airport",
+  "IAD": "Dulles International Airport"
+}
+```
+
+The example uses `code_to_name` to map the `Origin` column from the `flight-carriers` datasource to the corresponding full airport name. Returns `key not found` if no matching key exists in the lookup table.
+
+```sql
+SELECT 
+  "Origin" AS "origin_airport",
+  LOOKUP("Origin", 'code_to_name','key not found') AS "full_airport_name"
+FROM "flight-carriers"
+LIMIT 2
+```
+
+Returns the following:
+
+| `origin_airport` | `full_airport_name` | 
+| -- | -- |
+| `SJU` | `Luis Munoz Marin International Airport` |
+| `BOS` | `key not found` |
+
+</details> 
+
+[Learn more](sql-scalar.md#string-functions)
 
 ## LOWER
 

docs/querying/sql-scalar.md

@@ -102,7 +102,7 @@ String functions accept strings and return a type appropriate to the function.
 |`CHAR_LENGTH(expr)`|Alias for `LENGTH`.|
 |`CHARACTER_LENGTH(expr)`|Alias for `LENGTH`.|
 |`STRLEN(expr)`|Alias for `LENGTH`.|
-|`LOOKUP(expr, lookupName[, replaceMissingValueWith])`|Looks up `expr` in an existing [query-time lookup table](lookups.md) that has the name `lookupName`. Returns the optional constant `replaceMissingValueWith` when `expr` is null or when the lookup does not contain a value for `expr`.<br /><br />You can query lookups directly using the [`lookup` schema](sql.md#from).|
+|`LOOKUP(expr, lookupName[, replaceMissingValueWith])`|Searches for `expr` in a registered [query-time lookup table](lookups.md) named `lookupName` and returns the mapped value. If `expr` is null or not contained in the lookup, returns `replaceMissingValueWith` if supplied, otherwise returns null.<br /><br />You can query lookups directly using the [`lookup` schema](sql.md#from).|
 |`LOWER(expr)`|Returns `expr` in all lowercase.|
 |`UPPER(expr)`|Returns `expr` in all uppercase.|
 |`LPAD(expr, length[, chars])`|Returns a string of `length` from `expr`. If `expr` is shorter than `length`, left pads `expr` with `chars`, which defaults to space characters. If `expr` exceeds `length`, truncates `expr` to equal `length`.  If `chars` is an empty string, no padding is added. Returns `null` if either `expr` or `chars` is null.|