Function TruncateIndexValue

pkg/tablecodec/tablecodec.go:1777–1804

TruncateIndexValue truncate one value in the index.

(v *types.Datum, idxCol *model.IndexColumn, tblCol *model.ColumnInfo)

// TruncateIndexValue truncate one value in the index.
func TruncateIndexValue(v *types.Datum, idxCol *model.IndexColumn, tblCol *model.ColumnInfo) {
	noPrefixIndex := idxCol.Length == types.UnspecifiedLength
	if noPrefixIndex {
		return
	}
	notStringType := v.Kind() != types.KindString && v.Kind() != types.KindBytes
	if notStringType {
		return
	}
	colValue := v.GetBytes()
	if tblCol.GetCharset() == charset.CharsetBin || tblCol.GetCharset() == charset.CharsetASCII {
		// Count character length by bytes if charset is binary or ascii.
		if len(colValue) > idxCol.Length {
			// truncate value and limit its length
			if v.Kind() == types.KindBytes {
				v.SetBytes(colValue[:idxCol.Length])
			} else {
				v.SetString(v.GetString()[:idxCol.Length], tblCol.GetCollate())
			}
		}
	} else if utf8.RuneCount(colValue) > idxCol.Length {
		// Count character length by characters for other rune-based charsets, they are all internally encoded as UTF-8.
		rs := bytes.Runes(colValue)
		truncateStr := string(rs[:idxCol.Length])
		// truncate value and limit its length
		v.SetString(truncateStr, tblCol.GetCollate())
	}
}

// EncodeHandleInUniqueIndexValue encodes handle in data.
func EncodeHandleInUniqueIndexValue(h kv.Handle, isUntouched bool) []byte {