[#82] Added FROM clause to update builder (#256)

update.go

@@ -16,6 +16,7 @@ type updateData struct {
 	Prefixes          []Sqlizer
 	Table             string
 	SetClauses        []setClause
+	From              Sqlizer
 	WhereParts        []Sqlizer
 	OrderBys          []string
 	Limit             string
@@ -100,6 +101,14 @@ func (d *updateData) ToSql() (sqlStr string, args []interface{}, err error) {
 	}
 	sql.WriteString(strings.Join(setSqls, ", "))
 
+	if d.From != nil {
+		sql.WriteString(" FROM ")
+		args, err = appendToSql([]Sqlizer{d.From}, sql, "", args)
+		if err != nil {
+			return
+		}
+	}
+
 	if len(d.WhereParts) > 0 {
 		sql.WriteString(" WHERE ")
 		args, err = appendToSql(d.WhereParts, sql, " AND ", args)
@@ -233,6 +242,19 @@ func (b UpdateBuilder) SetMap(clauses map[string]interface{}) UpdateBuilder {
 	return b
 }
 
+// From adds FROM clause to the query
+// FROM is valid construct in postgresql only.
+func (b UpdateBuilder) From(from string) UpdateBuilder {
+	return builder.Set(b, "From", newPart(from)).(UpdateBuilder)
+}
+
+// FromSelect sets a subquery into the FROM clause of the query.
+func (b UpdateBuilder) FromSelect(from SelectBuilder, alias string) UpdateBuilder {
+	// Prevent misnumbered parameters in nested selects (#183).
+	from = from.PlaceholderFormat(Question)
+	return builder.Set(b, "From", Alias(from, alias)).(UpdateBuilder)
+}
+
 // Where adds WHERE expressions to the query.
 //
 // See SelectBuilder.Where for more information.

update_test.go

@@ -82,3 +82,26 @@ func TestUpdateBuilderNoRunner(t *testing.T) {
 	_, err := b.Exec()
 	assert.Equal(t, RunnerNotSet, err)
 }
+
+func TestUpdateBuilderFrom(t *testing.T) {
+	sql, _, err := Update("employees").Set("sales_count", 100).From("accounts").Where("accounts.name = ?", "ACME").ToSql()
+	assert.NoError(t, err)
+	assert.Equal(t, "UPDATE employees SET sales_count = ? FROM accounts WHERE accounts.name = ?", sql)
+}
+
+func TestUpdateBuilderFromSelect(t *testing.T) {
+	sql, _, err := Update("employees").
+		Set("sales_count", 100).
+		FromSelect(Select("id").
+			From("accounts").
+			Where("accounts.name = ?", "ACME"), "subquery").
+		Where("employees.account_id = subquery.id").ToSql()
+	assert.NoError(t, err)
+
+	expectedSql :=
+		"UPDATE employees " +
+			"SET sales_count = ? " +
+			"FROM (SELECT id FROM accounts WHERE accounts.name = ?) AS subquery " +
+			"WHERE employees.account_id = subquery.id"
+	assert.Equal(t, expectedSql, sql)
+}