diff --git a/conn.go b/conn.go
index e9641508..6b210043 100644
--- a/conn.go
+++ b/conn.go
@@ -90,54 +90,30 @@ func (c *conn) Close() (err error) {
 	return
 }
 
-func (c *conn) Query(sql string) (rows []map[string]string, err error) {
+func (c *conn) query(sql string, onDataRow func(*messageReader, []fieldDescription) error) (err error) {
 	if err = c.sendSimpleQuery(sql); err != nil {
 		return
 	}
 
+	var callbackError error
 	var fields []fieldDescription
-	rows = make([]map[string]string, 0)
+
 	for {
 		var t byte
 		var r *messageReader
 		if t, r, err = c.rxMsg(); err == nil {
 			switch t {
 			case readyForQuery:
-				return rows, nil
+				if err == nil {
+					err = callbackError
+				}
+				return
 			case rowDescription:
 				fields = c.rxRowDescription(r)
 			case dataRow:
-				rows = append(rows, c.rxDataRow(r, fields))
-			case commandComplete:
-				c.rxCommandComplete(r)
-			default:
-				if err = c.processContextFreeMsg(t, r); err != nil {
-					return nil, err
+				if callbackError == nil {
+					callbackError = onDataRow(r, fields)
 				}
-			}
-		} else {
-			return nil, err
-		}
-	}
-
-	panic("Unreachable")
-}
-
-func (c *conn) selectOne(sql string) (s string, err error) {
-	if err = c.sendSimpleQuery(sql); err != nil {
-		return
-	}
-
-	for {
-		var t byte
-		var r *messageReader
-		if t, r, err = c.rxMsg(); err == nil {
-			switch t {
-			case readyForQuery:
-				return
-			case rowDescription:
-			case dataRow:
-				s = c.rxDataRowFirstValue(r)
 			case commandComplete:
 			default:
 				if err = c.processContextFreeMsg(t, r); err != nil {
@@ -152,13 +128,28 @@ func (c *conn) selectOne(sql string) (s string, err error) {
 	panic("Unreachable")
 }
 
+func (c *conn) Query(sql string) (rows []map[string]string, err error) {
+	rows = make([]map[string]string, 0, 8)
+	onDataRow := func(r *messageReader, fields []fieldDescription) error {
+		rows = append(rows, c.rxDataRow(r, fields))
+		return nil
+	}
+	err = c.query(sql, onDataRow)
+	return
+}
+
 func (c *conn) SelectString(sql string) (s string, err error) {
-	return c.selectOne(sql)
+	onDataRow := func(r *messageReader, _ []fieldDescription) error {
+		s = c.rxDataRowFirstValue(r)
+		return nil
+	}
+	err = c.query(sql, onDataRow)
+	return
 }
 
 func (c *conn) selectInt(sql string, size int) (i int64, err error) {
 	var s string
-	s, err = c.selectOne(sql)
+	s, err = c.SelectString(sql)
 	if err != nil {
 		return
 	}
@@ -187,7 +178,7 @@ func (c *conn) SelectInt16(sql string) (i int16, err error) {
 
 func (c *conn) selectFloat(sql string, size int) (f float64, err error) {
 	var s string
-	s, err = c.selectOne(sql)
+	s, err = c.SelectString(sql)
 	if err != nil {
 		return
 	}
@@ -208,107 +199,72 @@ func (c *conn) SelectFloat32(sql string) (f float32, err error) {
 }
 
 func (c *conn) SelectAllString(sql string) (strings []string, err error) {
-	if err = c.sendSimpleQuery(sql); err != nil {
-		return
+	strings = make([]string, 0, 8)
+	onDataRow := func(r *messageReader, _ []fieldDescription) error {
+		strings = append(strings, c.rxDataRowFirstValue(r))
+		return nil
 	}
-
-	strings = make([]string, 0)
-
-	for {
-		var t byte
-		var r *messageReader
-		if t, r, err = c.rxMsg(); err == nil {
-			switch t {
-			case readyForQuery:
-				return
-			case rowDescription:
-			case dataRow:
-				strings = append(strings, c.rxDataRowFirstValue(r))
-			case commandComplete:
-			default:
-				if err = c.processContextFreeMsg(t, r); err != nil {
-					return
-				}
-			}
-		} else {
-			return
-		}
-	}
-
-	panic("Unreachable")
-}
-
-func (c *conn) selectAllInt(sql string, size int) (ints []int64, err error) {
-	var strings []string
-	strings, err = c.SelectAllString(sql)
-	if err != nil {
-		return
-	}
-
-	ints = make([]int64, len(strings))
-	for i, s := range strings {
-		ints[i], err = strconv.ParseInt(s, 10, size)
-		if err != nil {
-			return
-		}
-	}
-
+	err = c.query(sql, onDataRow)
 	return
 }
 
 func (c *conn) SelectAllInt64(sql string) (ints []int64, err error) {
-	return c.selectAllInt(sql, 64)
+	ints = make([]int64, 0, 8)
+	onDataRow := func(r *messageReader, _ []fieldDescription) (parseError error) {
+		var i int64
+		i, parseError = strconv.ParseInt(c.rxDataRowFirstValue(r), 10, 64)
+		ints = append(ints, i)
+		return
+	}
+	err = c.query(sql, onDataRow)
+	return
 }
 
 func (c *conn) SelectAllInt32(sql string) (ints []int32, err error) {
-	var int64s []int64
-	int64s, err = c.selectAllInt(sql, 32)
-	ints = make([]int32, len(int64s))
-	for i := 0; i < len(int64s); i++ {
-		ints[i] = int32(int64s[i])
+	ints = make([]int32, 0, 8)
+	onDataRow := func(r *messageReader, fields []fieldDescription) (parseError error) {
+		var i int64
+		i, parseError = strconv.ParseInt(c.rxDataRowFirstValue(r), 10, 32)
+		ints = append(ints, int32(i))
+		return
 	}
+	err = c.query(sql, onDataRow)
 	return
 }
 
 func (c *conn) SelectAllInt16(sql string) (ints []int16, err error) {
-	var int64s []int64
-	int64s, err = c.selectAllInt(sql, 16)
-	ints = make([]int16, len(int64s))
-	for i := 0; i < len(int64s); i++ {
-		ints[i] = int16(int64s[i])
-	}
-	return
-}
-
-func (c *conn) selectAllFloat(sql string, size int) (floats []float64, err error) {
-	var strings []string
-	strings, err = c.SelectAllString(sql)
-	if err != nil {
+	ints = make([]int16, 0, 8)
+	onDataRow := func(r *messageReader, _ []fieldDescription) (parseError error) {
+		var i int64
+		i, parseError = strconv.ParseInt(c.rxDataRowFirstValue(r), 10, 16)
+		ints = append(ints, int16(i))
 		return
 	}
-
-	floats = make([]float64, len(strings))
-	for i, s := range strings {
-		floats[i], err = strconv.ParseFloat(s, size)
-		if err != nil {
-			return
-		}
-	}
-
+	err = c.query(sql, onDataRow)
 	return
 }
 
 func (c *conn) SelectAllFloat64(sql string) (floats []float64, err error) {
-	return c.selectAllFloat(sql, 64)
+	floats = make([]float64, 0, 8)
+	onDataRow := func(r *messageReader, _ []fieldDescription) (parseError error) {
+		var f float64
+		f, parseError = strconv.ParseFloat(c.rxDataRowFirstValue(r), 64)
+		floats = append(floats, f)
+		return
+	}
+	err = c.query(sql, onDataRow)
+	return
 }
 
 func (c *conn) SelectAllFloat32(sql string) (floats []float32, err error) {
-	var float64s []float64
-	float64s, err = c.selectAllFloat(sql, 32)
-	floats = make([]float32, len(float64s))
-	for i := 0; i < len(float64s); i++ {
-		floats[i] = float32(float64s[i])
+	floats = make([]float32, 0, 8)
+	onDataRow := func(r *messageReader, _ []fieldDescription) (parseError error) {
+		var f float64
+		f, parseError = strconv.ParseFloat(c.rxDataRowFirstValue(r), 32)
+		floats = append(floats, float32(f))
+		return
 	}
+	err = c.query(sql, onDataRow)
 	return
 }