dialect/sql: add alter-index for renaming psql indexes (#301)

dialect/sql/builder.go

@@ -289,6 +289,39 @@ func (t *TableAlter) Query() (string, []interface{}) {
 	return t.String(), t.args
 }
 
+// IndexAlter is a query builder for `ALTER INDEX` statement.
+type IndexAlter struct {
+	Builder
+	name    string    // index to alter.
+	Queries []Querier // alter options.
+}
+
+// AlterIndex returns a query builder for the `ALTER INDEX` statement.
+//
+//	AlterIndex("old_key").
+//		Rename("new_key")
+//
+func AlterIndex(name string) *IndexAlter { return &IndexAlter{name: name} }
+
+// Rename appends the `RENAME TO` clause to the `ALTER INDEX` statement.
+func (i *IndexAlter) Rename(name string) *IndexAlter {
+	i.Queries = append(i.Queries, Raw(fmt.Sprintf("RENAME TO %s", i.Quote(name))))
+	return i
+}
+
+// Query returns query representation of the `ALTER INDEX` statement.
+//
+//	ALTER INDEX name
+//    [alter_specification]
+//
+func (i *IndexAlter) Query() (string, []interface{}) {
+	i.WriteString("ALTER INDEX ")
+	i.Ident(i.name)
+	i.Pad()
+	i.JoinComma(i.Queries...)
+	return i.String(), i.args
+}
+
 // ForeignKeyBuilder is the builder for the foreign-key constraint clause.
 type ForeignKeyBuilder struct {
 	Builder
@@ -2000,6 +2033,18 @@ func (d *DialectBuilder) AlterTable(name string) *TableAlter {
 	return b
 }
 
+// AlterIndex creates an IndexAlter for the configured dialect.
+//
+//	Dialect(dialect.Postgres).
+//		AlterIndex("old").
+//		Rename("new")
+//
+func (d *DialectBuilder) AlterIndex(name string) *IndexAlter {
+	b := AlterIndex(name)
+	b.SetDialect(d.dialect)
+	return b
+}
+
 // Column creates a ColumnBuilder for the configured dialect.
 //
 //	Dialect(dialect.Postgres)..

dialect/sql/builder_test.go

@@ -195,6 +195,11 @@ func TestBuilder(t *testing.T) {
 			input:     AlterTable("users").RenameIndex("old", "new"),
 			wantQuery: "ALTER TABLE `users` RENAME INDEX `old` TO `new`",
 		},
+		{
+			input: Dialect(dialect.Postgres).AlterIndex("old").
+				Rename("new"),
+			wantQuery: `ALTER INDEX "old" RENAME TO "new"`,
+		},
 		{
 			input:     Insert("users").Columns("age").Values(1),
 			wantQuery: "INSERT INTO `users` (`age`) VALUES (?)",