Aleksey Midenkov a3c379ea61 MDEV-23799 CREATE .. SELECT wrong result on join versioned table ...

For join to work correctly versioning condition must be added to table
on_expr. Without that JOIN_CACHE gets expression (1)

  trigcond(xtitle.row_end = TIMESTAMP'2038-01-19 06:14:07.999999') and
  trigcond(xtitle.elementId = x.`id` and xtitle.pkey = 'title')

instead of (2)

  trigcond(xtitle.elementId = x.`id` and xtitle.pkey = 'title')

for join_null_complements(). It is NULL-row of xtitle for
complementing the join and the above comparisons of course FALSE, but
trigcond (Item_func_trig_cond) makes them TRUE via its trig_var
property which is bound to some boolean properties of JOIN_TAB.

Expression (2) evaluated to TRUE because its trig_var is bound to
first_inner_tab->not_null_compl. The expression (1) does not evaluate
correctly because row_end comparison's trig_var is bound to
first_inner->found earlier. As a result JOIN_CACHE::check_match()
skipped the row for join_null_complements().

When we add versioning condition to table's on_expr the optimizer in
make_join_select() distributes conditions differently. tmp_cond
inherits on_expr value and in Good case it is full expression

xgender.elementId = x.`id` and xgender.pkey = 'gender' and
xgender.row_end = TIMESTAMP'2038-01-19 06:14:07.999999'

while in Bad case it is only

xgender.elementId = x.`id` and xgender.pkey = 'gender'.

Later in Good row_end condition is optimized out and we get one
trigcond in form of (2).

2020-10-20 10:49:54 +03:00

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