Fix where example (#129)

Author: tothmano

apl/tabular-operators/where-operator.mdx

@@ -135,6 +135,8 @@ This query helps filter logs to investigate activity originating from a specific
 
 The `* has` pattern in APL is a dynamic and powerful tool within the `where` operator. It offers you the flexibility to search for specific substrings across all fields in a dataset without the need to specify each field name individually. This becomes especially advantageous when dealing with datasets that have numerous or dynamically named fields.
 
+`where * has` is an expensive operation because it searches all fields. For a more efficient query, explicitly list the fields in which you want to search. For example: `where firstName has "miguel" or lastName has "miguel"`. 
+
 ### Basic where * has usage
 
 Find events where any field contains a specific substring.
@@ -186,26 +188,26 @@ Find the average of a specific field for events where any field contains a certa
 
 ```kusto
 ['sample-http-logs']
-| where * has "japan"
+| where * has "Japan"
 | summarize avg(req_duration_ms)
 ```
 
-[Run in Playground](https://play.axiom.co/axiom-play-qf1k/explorer?initForm=%7B%22apl%22%3A%22%5B%27sample-http-logs%27%5D%5Cn%7C%20where%20%2A%20has%20%5C%22japan%5C%22%5Cn%7C%20summarize%20avg%28req_duration_ms%29%22%7D&queryOptions=%7B%22quickRange%22%3A%2230d%22%7D)
+[Run in Playground](https://play.axiom.co/axiom-play-qf1k/explorer?initForm=%7B%22apl%22%3A%22%5B%27sample-http-logs%27%5D%5Cn%7C%20where%20%2A%20has%20%5C%22Japan%5C%22%5Cn%7C%20summarize%20avg%28req_duration_ms%29%22%7D&queryOptions=%7B%22quickRange%22%3A%2230d%22%7D)
 
 ### String case transformation
 
-If you’re unsure about the case of the substring in the dataset, convert everything to lowercase for comparison.
+The `has` operator is case insensitive. Use `has` if you’re unsure about the case of the substring in the dataset. For the case-sensitive operator, use `has_cs`.
 
 ```kusto
 ['sample-http-logs']
-| where * has "japan"
+| where * has "mexico"
 | summarize avg(req_duration_ms)
 ```
 
-[Run in Playground](https://play.axiom.co/axiom-play-qf1k/explorer?initForm=%7B%22apl%22%3A%22%5B%27sample-http-logs%27%5D%5Cn%7C%20where%20%2A%20has%20%5C%22japan%5C%22%5Cn%7C%20summarize%20avg%28req_duration_ms%29%22%7D&queryOptions=%7B%22quickRange%22%3A%2230d%22%7D)
+[Run in Playground](https://play.axiom.co/axiom-play-qf1k/explorer?initForm=%7B%22apl%22%3A%22%5B%27sample-http-logs%27%5D%5Cn%7C%20where%20%2A%20has%20%5C%22mexico%5C%22%5Cn%7C%20summarize%20avg%28req_duration_ms%29%22%7D&queryOptions=%7B%22quickRange%22%3A%2230d%22%7D)
 
 ## List of related operators
 
 - [**count**](/apl/tabular-operators/count-operator): Use `count` to return the number of records that match specific criteria.
 - [**distinct**](/apl/tabular-operators/distinct-operator): Use `distinct` to return unique values in a dataset, complementing filtering.
-- [**take**](/apl/tabular-operators/take-operator): Use `take` to return a specific number of records, typically in combination with `where` for pagination.
+- [**take**](/apl/tabular-operators/take-operator): Use `take` to return a specific number of records, typically in combination with `where` for pagination.