Comment 7 for bug 951937

Before the equality substitutiuon, the WHERE clause has this form (both in maria-5.3 and mysql-5.6):

"(((t1a.b >= t1a.a) or multiple equal('z', t1b.b, t1a.a, v.a, t1b.a)) and multiple equal(t1b.b, t1a.a, v.a, t1b.a))"

the multiple-equal inside the OR clause is the same as the outer one, except that it also includes constant 'z'.

After equality substitution for the inner multiple equal('z', t1b.b, t1a.a, v.a, t1b.a) , we get

In MariaDB:
  $537 = 0x8b9f560 "((t1a.a = 'z') and (v.a = 'z'))"

In MySQL:
  $117 = 0x8f7bea0 "((t1a.a = 'z') and (t1b.b = 'z') and (t1b.a = 'z'))"