Fix return type for subqueries in MySQL (#1383)

internal/compiler/output_columns.go

@@ -268,6 +268,17 @@ func outputColumns(qc *QueryCatalog, node ast.Node) ([]*Column, error) {
 			}
 			cols = append(cols, col)
 
+		case *ast.SelectStmt:
+			subcols, err := outputColumns(qc, n)
+			if err != nil {
+				return nil, err
+			}
+			first := subcols[0]
+			if res.Name != nil {
+				first.Name = *res.Name
+			}
+			cols = append(cols, first)
+
 		default:
 			name := ""
 			if res.Name != nil {

internal/endtoend/testdata/select_nested_count/mysql/query.sql

@@ -0,0 +1,19 @@
+CREATE TABLE authors (
+  id   bigint    PRIMARY KEY,
+  name text      NOT NULL,
+  bio  text
+);
+
+CREATE TABLE books (
+  id bigint PRIMARY KEY,
+  author_id bigint NOT NULL
+    REFERENCES authors(id),
+  title text NOT NULL
+);
+
+-- name: GetAuthorsWithBooksCount :many
+SELECT *, (
+  SELECT COUNT(id) FROM books
+  WHERE books.author_id = id
+) AS books_count
+FROM authors;

internal/endtoend/testdata/select_nested_count/mysql/sqlc.json

@@ -0,0 +1,12 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "name": "querytest",
+      "schema": "query.sql",
+      "queries": "query.sql",
+      "engine": "mysql"
+    }
+  ]
+}