docs: added a documentation section on debugging query builder (#9846)

* Added a section on debugging query builder

It covers using getQuery() and getQueryAndParameters() which are both useful when trying to figure out why your query isn't doing what you might expect it should do.

* forgot await

* fix typo

docs/select-query-builder.md

@@ -29,6 +29,7 @@
 -   [Using subqueries](#using-subqueries)
 -   [Hidden Columns](#hidden-columns)
 -   [Querying Deleted rows](#querying-deleted-rows)
+-   [Debugging](#debugging)
 
 ## What is `QueryBuilder`
 
@@ -1292,3 +1293,43 @@ console.log(account)
 By default `timeTravelQuery()` uses `follower_read_timestamp()` function if no arguments passed.
 For another supported timestamp arguments and additional information please refer to
 [CockroachDB](https://www.cockroachlabs.com/docs/stable/as-of-system-time.html) docs.
+
+## Debugging
+
+You can get the generated SQL from the query builder by calling `getQuery()` or `getQueryAndParameters()`.
+
+If you just want the query you can use `getQuery()`
+
+```typescript
+const sql = await dataSource
+    .getRepository(User)
+    .createQueryBuilder("user")
+    .where("user.id = :id", { id: 1 })
+    .getQuery()
+```
+
+Which results in:
+
+```sql
+SELECT `user`.`id` as `userId`, `user`.`firstName` as `userFirstName`, `user`.`lastName` as `userLastName` FROM `users` `user` WHERE `user`.`id` = ?
+```
+
+Or if you want the query and the parameters you can get an array back using `getQueryAndParameters()`
+
+```typescript
+const queryAndParams = await dataSource
+    .getRepository(User)
+    .createQueryBuilder("user")
+    .where("user.id = :id", { id: 1 })
+    .getQueryAndParameters()
+```
+
+Which results in:
+
+```typescript
+[
+ "SELECT `user`.`id` as `userId`, `user`.`firstName` as `userFirstName`, `user`.`lastName` as `userLastName` FROM `users` `user` WHERE `user`.`id` = ?",
+ [ 1 ]
+]
+```
+