Merge BUG#12997905 from 5.1 to 5.5

1 files changed, 17 insertions, 0 deletions

diff --git a/sql/field.h b/sql/field.h
index 9c2cd52cfa5..b4adb764b22 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -2227,6 +2227,23 @@ public:
   uchar *from_null_ptr,*to_null_ptr;
   my_bool *null_row;
   uint	from_bit,to_bit;
+  /**
+    Number of bytes in the fields pointed to by 'from_ptr' and
+    'to_ptr'. Usually this is the number of bytes that are copied from
+    'from_ptr' to 'to_ptr'.
+
+    For variable-length fields (VARCHAR), the first byte(s) describe
+    the actual length of the text. For VARCHARs with length 
+       < 256 there is 1 length byte 
+       >= 256 there is 2 length bytes
+    Thus, if from_field is VARCHAR(10), from_length (and in most cases
+    to_length) is 11. For VARCHAR(1024), the length is 1026. @see
+    Field_varstring::length_bytes
+
+    Note that for VARCHARs, do_copy() will be do_varstring*() which
+    only copies the length-bytes (1 or 2) + the actual length of the
+    text instead of from/to_length bytes. @see get_copy_func()
+  */
   uint from_length,to_length;
   Field *from_field,*to_field;
   String tmp;					// For items