fix(engine/mysql): Support nullable fields in joins for MySQL engine (#1249)

* Fix nullable fields in joins for MySQL engine

Author: timstudd

examples/booktest/mysql/db_test.go

@@ -1,3 +1,4 @@
+//go:build examples
 // +build examples
 
 package booktest
@@ -150,7 +151,7 @@ func TestBooks(t *testing.T) {
 		t.Fatal(err)
 	}
 	for _, ab := range res {
-		t.Logf("Book %d: '%s', Author: '%s', ISBN: '%s' Tags: '%v'\n", ab.BookID, ab.Title, ab.Name, ab.Isbn, ab.Tags)
+		t.Logf("Book %d: '%s', Author: '%s', ISBN: '%s' Tags: '%v'\n", ab.BookID, ab.Title, ab.Name.String, ab.Isbn, ab.Tags)
 	}
 
 	// TODO: call say_hello(varchar)

examples/booktest/mysql/query.sql.go

@@ -22,7 +22,7 @@ WHERE tags = ?
 data class BooksByTagsRow (
   val bookId: Int,
   val title: String,
-  val name: String,
+  val name: String?,
   val isbn: String,
   val tags: String
 )

examples/kotlin/src/main/kotlin/com/example/booktest/mysql/QueriesImpl.kt

@@ -302,7 +302,14 @@ func isTableRequired(n ast.Node, tableName string, prior int) int {
 		case ast.JoinTypeFull:
 			return helper(tableOptional, tableOptional)
 		}
+	case *ast.List:
+		for _, item := range n.Items {
+			if res := isTableRequired(item, tableName, prior); res != tableNotFound {
+				return res
+			}
+		}
 	}
+
 	return tableNotFound
 }