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package pq
import (
const headerSize = 4
type fieldDesc struct {
// The object ID of the data type.
OID oid.Oid
// The data type size (see pg_type.typlen).
// Note that negative values denote variable-width types.
Len int
// The type modifier (see pg_attribute.atttypmod).
// The meaning of the modifier is type-specific.
Mod int
func (fd fieldDesc) Type() reflect.Type {
switch fd.OID {
case oid.T_int8:
return reflect.TypeOf(int64(0))
case oid.T_int4:
return reflect.TypeOf(int32(0))
case oid.T_int2:
return reflect.TypeOf(int16(0))
case oid.T_varchar, oid.T_text:
return reflect.TypeOf("")
case oid.T_bool:
return reflect.TypeOf(false)
case oid.T_date, oid.T_time, oid.T_timetz, oid.T_timestamp, oid.T_timestamptz:
return reflect.TypeOf(time.Time{})
case oid.T_bytea:
return reflect.TypeOf([]byte(nil))
return reflect.TypeOf(new(interface{})).Elem()
func (fd fieldDesc) Name() string {
return oid.TypeName[fd.OID]
func (fd fieldDesc) Length() (length int64, ok bool) {
switch fd.OID {
case oid.T_text, oid.T_bytea:
return math.MaxInt64, true
case oid.T_varchar, oid.T_bpchar:
return int64(fd.Mod - headerSize), true
return 0, false
func (fd fieldDesc) PrecisionScale() (precision, scale int64, ok bool) {
switch fd.OID {
case oid.T_numeric, oid.T__numeric:
mod := fd.Mod - headerSize
precision = int64((mod >> 16) & 0xffff)
scale = int64(mod & 0xffff)
return precision, scale, true
return 0, 0, false
// ColumnTypeScanType returns the value type that can be used to scan types into.
func (rs *rows) ColumnTypeScanType(index int) reflect.Type {
return rs.colTyps[index].Type()
// ColumnTypeDatabaseTypeName return the database system type name.
func (rs *rows) ColumnTypeDatabaseTypeName(index int) string {
return rs.colTyps[index].Name()
// ColumnTypeLength returns the length of the column type if the column is a
// variable length type. If the column is not a variable length type ok
// should return false.
func (rs *rows) ColumnTypeLength(index int) (length int64, ok bool) {
return rs.colTyps[index].Length()
// ColumnTypePrecisionScale should return the precision and scale for decimal
// types. If not applicable, ok should be false.
func (rs *rows) ColumnTypePrecisionScale(index int) (precision, scale int64, ok bool) {
return rs.colTyps[index].PrecisionScale()
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