If we compare two items A and B, with B being (a constant) of a
larger type, then A gets promoted to B's type for comparison if
it's a constant, function, or CAST() column, but B gets demoted
to A's type if A is a (not explicitly CAST()) column. This is
counter-intuitive and not mandated by the standard.
 
Disabling optimisation where it would be lossy so field value
will properly get promoted and compared as binary string (rather
than as integers).


mysql-test/include/ps_conv.inc:
  Bug #21103: DATE column not compared as DATE
  
  When comparing a DATE field with a DATETIME constant, we now compare
  as DATETIMEs, not as DATEs.  Fix certain queries to still work.
mysql-test/r/func_time.result:
  Bug #21103: DATE column not compared as DATE
  
  When comparing a DATE field with a DATETIME constant, we now compare
  as DATETIMEs, not as DATEs.  Show that everything works as expected.
mysql-test/r/ps_2myisam.result:
  Bug #21103: DATE column not compared as DATE
  
  When comparing a DATE field with a DATETIME constant, we now compare
  as DATETIMEs, not as DATEs.  Fix certain queries to still work.
mysql-test/r/ps_3innodb.result:
  Bug #21103: DATE column not compared as DATE
  
  When comparing a DATE field with a DATETIME constant, we now compare
  as DATETIMEs, not as DATEs.  Fix certain queries to still work.
mysql-test/r/ps_4heap.result:
  Bug #21103: DATE column not compared as DATE
  
  When comparing a DATE field with a DATETIME constant, we now compare
  as DATETIMEs, not as DATEs.  Fix certain queries to still work.
mysql-test/r/ps_5merge.result:
  Bug #21103: DATE column not compared as DATE
  
  When comparing a DATE field with a DATETIME constant, we now compare
  as DATETIMEs, not as DATEs.  Fix certain queries to still work.
mysql-test/r/ps_7ndb.result:
  Bug #21103: DATE column not compared as DATE
  
  When comparing a DATE field with a DATETIME constant, we now compare
  as DATETIMEs, not as DATEs.  Fix certain queries to still work.
mysql-test/t/func_time.test:
  Bug #21103: DATE column not compared as DATE
  
  When comparing a DATE field with a DATETIME constant, we now compare
  as DATETIMEs, not as DATEs.  Show that everything works as expected.
sql/field.cc:
  Bug #21103: DATE column not compared as DATE
  
  #0 stores the date only as a 3-byte integer; save_in_field() in
  #1 saves 'this' in field's format (DATE), #2 "converts a constant
  item to an int and replaces the original item" -- consequently,
  this replaces the Item_string "2006-11-06 04:08:36.0" with the
  Item_int_with_ref 20061106.
  
  #0  Field_newdate::store (this=0x8d26880, from=0x8d5e658 "2006-11-06
  04:08:36.0", len=21, cs=0x88022c0) at field.cc:5344
  #1  0x0817e3b0 in Item_string::save_in_field (this=0x8d5e670, field=0x8d26880, no_conversions=true) at item.cc:4340
  #2  0x081b22ae in convert_constant_item (thd=0x8d25240, field=0x8d26880, item=0x8d5e74c) at item_cmpfunc.cc:245
  #3  0x081b8a36 in Item_bool_func2::fix_length_and_dec (this=0x8d5e6f8) at item_cmpfunc.cc:309
  #4  0x081a3427 in Item_func::fix_fields (this=0x8d5e6f8, thd=0x8d25240, ref=0x8d5f5fc) at item_func.cc:190
  #5  0x0825bc2d in setup_conds (thd=0x8d25240, tables=0x8d5e410, leaves=0x8d5e410, conds=0x8d5f5fc) at sql_base.cc:4941
  ...
  
  Disabling optimisation where it would be lossy so field value will
  properly get promoted and compared as binary string (rather than as
  integers).