docs: Add a note on placeholders in a generated query

Author: igorlukanin

docs/pages/product/workspace/playground.mdx

@@ -156,6 +156,13 @@ on the <Btn>Generated SQL</Btn> tab. Click <Btn>Copy</Btn> to put it into your c
   src="https://ucarecdn.com/d2b6e514-9219-49ea-bae6-bcd0f1936542/"
 />
 
+<InfoBox>
+
+Note that a generated query can contain placeholders, e.g., `?` or `$1`, for parameters
+that Cube passes to an underlying data source driver later when executing the query.
+
+</InfoBox>
+
 ## Copying API queries
 
 View the queries for respective data APIs on the <Btn>SQL API</Btn>, <Btn>REST API</Btn>,

docs/pages/reference/rest-api.mdx

@@ -145,6 +145,13 @@ Example response:
 }
 ```
 
+<InfoBox>
+
+Note that a generated query can contain placeholders, e.g., `?` or `$1`, for parameters
+that Cube passes to an underlying data source driver later when executing the query.
+
+</InfoBox>
+
 ## `/v1/meta`
 
 Get meta-information for cubes and views defined in the data model. Information about cubes and views with `public: false` will not be returned.