From 7e55057118c5d4d91521f6b78aa00da066a5e53e Mon Sep 17 00:00:00 2001
From: Amitai Burstein <amitai@gizra.com>
Date: Tue, 4 Jul 2023 22:26:56 +0300
Subject: [PATCH] Add example for fetching a single column with sqlQuery

---
 Guide/database.markdown | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/Guide/database.markdown b/Guide/database.markdown
index 44a7c5b3e..efd642c57 100644
--- a/Guide/database.markdown
+++ b/Guide/database.markdown
@@ -320,6 +320,19 @@ do
     result :: [Project] <- sqlQuery "SELECT * FROM ?" [PG.Identifier table]
 ```
 
+If you need to fetch only a single column, for example only the ID of a record, you need to help the compiler and type hint
+the result, with an `Only` prefix. Here's an example of fetching only the IDs of a `project` table, and converting them to
+`Id Project`
+
+```haskell
+allProjectUuids :: [Only UUID] <- sqlQuery "SELECT projects.id FROM projects" ()
+
+let projectIds =
+        allProjectUuids
+            -- Extract the UUIDs, and convert to an ID.
+            |> map (\(Only uuid) -> Id uuid :: Id Project)
+```
+
 ### Scalar Results
 
 The [`sqlQuery`](https://ihp.digitallyinduced.com/api-docs/IHP-ModelSupport.html#v:sqlQuery) function always returns a list of rows as the result. When the result of your query is a single value (such as an integer or string) use [`sqlQueryScalar`](https://ihp.digitallyinduced.com/api-docs/IHP-ModelSupport.html#v:sqlQueryScalar):