fixing the code to make the subselect nullable

Author: ryu-ichiroh

internal/compiler/output_columns.go

@@ -3,6 +3,7 @@ package compiler
 import (
 	"errors"
 	"fmt"
+	"strings"
 
 	"github.com/sqlc-dev/sqlc/internal/sql/ast"
 	"github.com/sqlc-dev/sqlc/internal/sql/astutils"
@@ -315,12 +316,14 @@ func (c *Compiler) outputColumns(qc *QueryCatalog, node ast.Node) ([]*Column, er
 					DataType:   dataType(fun.ReturnType),
 					NotNull:    !fun.ReturnTypeNullable,
 					IsFuncCall: true,
+					FuncName:   rel.Name,
 				})
 			} else {
 				cols = append(cols, &Column{
 					Name:       name,
 					DataType:   "any",
 					IsFuncCall: true,
+					FuncName:   rel.Name,
 				})
 			}
 
@@ -341,6 +344,10 @@ func (c *Compiler) outputColumns(qc *QueryCatalog, node ast.Node) ([]*Column, er
 				if res.Name != nil {
 					first.Name = *res.Name
 				}
+				if !(first.IsFuncCall && strings.EqualFold(first.FuncName, "count")) {
+					first.NotNull = false
+				}
+
 				cols = append(cols, first)
 			default:
 				cols = append(cols, &Column{Name: name, DataType: "any", NotNull: false})
@@ -377,8 +384,9 @@ func (c *Compiler) outputColumns(qc *QueryCatalog, node ast.Node) ([]*Column, er
 			if res.Name != nil {
 				first.Name = *res.Name
 			}
-
-			if hasWhereOrHavingClause(n) {
+			if !(first.IsFuncCall &&
+				(strings.EqualFold(first.FuncName, "count") ||
+					strings.EqualFold(first.FuncName, "total"))) {
 				first.NotNull = false
 			}
 
@@ -769,17 +777,3 @@ func findColumnForRef(ref *ast.ColumnRef, tables []*Table, targetList *ast.List)
 
 	return nil
 }
-
-// hasWhereOrHavingClause returns true if the statement contains WHERE or HAVING clause
-func hasWhereOrHavingClause(node ast.Node) bool {
-	stmt := node.(*ast.SelectStmt)
-
-	if _, isTODO := stmt.WhereClause.(*ast.TODO); stmt.WhereClause != nil && !isTODO {
-		return true
-	}
-	if _, isTODO := stmt.HavingClause.(*ast.TODO); stmt.HavingClause != nil && !isTODO {
-		return true
-	}
-
-	return false
-}

internal/compiler/query.go

@@ -29,6 +29,7 @@ type Column struct {
 	Length       *int
 	IsNamedParam bool
 	IsFuncCall   bool
+	FuncName     string
 
 	// XXX: Figure out what PostgreSQL calls `foo.id`
 	Scope      string

internal/endtoend/testdata/nullable_subselect/mysql/go/models.go

@@ -1,7 +1,10 @@
-CREATE TABLE foo (a int not null, b int);
+-- name: FirstRowFromFooTable :many
+SELECT a, (SELECT a FROM foo limit 1) as "first" FROM foo;
 
--- name: SubqueryWithWhereClause :many
-SELECT a, (SELECT COUNT(a) FROM foo WHERE a > 10) as "total" FROM foo;
+-- name: FirstRowFromEmptyTable :many
+SELECT a, (SELECT a FROM empty limit 1) as "first" FROM foo;
 
--- name: SubqueryWithHavingClause :many
-SELECT a, (SELECT COUNT(a) FROM foo GROUP BY b HAVING COUNT(a) > 10) as "total" FROM foo;
+-- In MySQL, only count() returns 0 for empty table.
+-- https://dev.mysql.com/doc/refman/8.0/en/aggregate-functions.html
+-- name: CountRowsEmptyTable :many
+SELECT a, (SELECT count(a) FROM empty) as "count" FROM foo;

internal/endtoend/testdata/nullable_subselect/mysql/go/query.sql.go

@@ -0,0 +1,7 @@
+CREATE TABLE foo (a int not NULL, b int);
+
+INSERT INTO foo VALUES (1, 2);
+INSERT INTO foo VALUES (3, NULL);
+INSERT INTO foo VALUES (4, 5);
+
+CREATE TABLE empty (a int not NULL, b int);

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

@@ -5,7 +5,7 @@
       "path": "go",
       "engine": "mysql",
       "name": "querytest",
-      "schema": "query.sql",
+      "schema": "schema.sql",
       "queries": "query.sql"
     }
   ]

internal/endtoend/testdata/nullable_subselect/mysql/schema.sql

@@ -1,7 +1,10 @@
-CREATE TABLE foo (a int not null, b int);
+-- name: FirstRowFromFooTable :many
+SELECT a, (SELECT a FROM foo limit 1) as "first" FROM foo;
 
--- name: SubqueryWithWhereClause :many
-SELECT a, (SELECT COUNT(a) FROM foo WHERE a > 10) as "total" FROM foo;
+-- name: FirstRowFromEmptyTable :many
+SELECT a, (SELECT a FROM empty limit 1) as "first" FROM foo;
 
--- name: SubqueryWithHavingClause :many
-SELECT a, (SELECT COUNT(a) FROM foo GROUP BY b HAVING COUNT(a) > 10) as "total" FROM foo;
+-- In PostgreSQL, only count() returns 0 for empty table.
+-- https://www.postgresql.org/docs/15/functions-aggregate.html
+-- name: CountRowsEmptyTable :many
+SELECT a, (SELECT count(a) FROM empty) as "count" FROM foo;