parser: fix SET=DEFAULT syntax (#551)

[Deardrops]

What problem does this PR solve?

Cherry-pick #551

Fix compatibility problem about SET=DEFAULT syntax

Issue: pingcap/parser#549

MySQL Syntax:

insert_stmt:
          ...
        | INSERT_SYM                   /* #1 */
          insert_lock_option           /* #2 */
          opt_ignore                   /* #3 */
          opt_INTO                     /* #4 */
          table_ident                  /* #5 */
          opt_use_partition            /* #6 */
          SET_SYM                      /* #7 */
          update_list                  /* #8 */
          opt_insert_update_list       /* #9 */
          {
            PT_insert_values_list *one_row= NEW_PTN PT_insert_values_list;
            if (one_row == NULL || one_row->push_back(&$8.value_list->value))
              MYSQL_YYABORT; // OOM
            $$= NEW_PTN PT_insert(false, $1, $2, $3, $5, $6,
                                  $8.column_list, one_row,
                                  NULL,
                                  $9.column_list, $9.value_list);
          }
        | ...
        ;
...
replace_stmt:
          ...
        | REPLACE_SYM                   /* #1 */
          replace_lock_option           /* #2 */
          opt_INTO                      /* #3 */
          table_ident                   /* #4 */
          opt_use_partition             /* #5 */
          SET_SYM                       /* #6 */
          update_list                   /* #7 */
          {
            PT_insert_values_list *one_row= NEW_PTN PT_insert_values_list;
            if (one_row == NULL || one_row->push_back(&$7.value_list->value))
              MYSQL_YYABORT; // OOM
            $$= NEW_PTN PT_insert(true, $1, $2, false, $4, $5,
                                  $7.column_list, one_row,
                                  NULL,
                                  NULL, NULL);
          }
        | ...
        ;
...
update_stmt:
          opt_with_clause
          UPDATE_SYM            /* #1 */
          opt_low_priority      /* #2 */
          opt_ignore            /* #3 */
          table_reference_list  /* #4 */
          SET_SYM               /* #5 */
          update_list           /* #6 */
          opt_where_clause      /* #7 */
          opt_order_clause      /* #8 */
          opt_simple_limit      /* #9 */
          {
            $$= NEW_PTN PT_update($1, $2, $3, $4, $5, $7.column_list, $7.value_list,
                                  $8, $9, $10);
          }
        ;

update_list:
          update_list ',' update_elem
          {
            ...
          }
        | update_elem
          {
            ...
          }
        ;

update_elem:
          simple_ident_nospvar equal expr_or_default
          {
            $$.column= $1;
            $$.value= $3;
          }
        ;

Bad SQL Case:

insert into t set a = default;
replace t set a = default;
update t set a = default;

Check List

Tests

• Unit test

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-3.0@9dc33a6). Click here to learn what that means.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             release-3.0     #648   +/-   ##
==============================================
  Coverage               ?   63.89%           
==============================================
  Files                  ?       31           
  Lines                  ?    10831           
  Branches               ?        0           
==============================================
  Hits                   ?     6920           
  Misses                 ?     3502           
  Partials               ?      409

Impacted Files	Coverage Δ
parser.go	86.4% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9dc33a6...18147ef. Read the comment docs.

[bb7133]

LGTM

[Deardrops]

@kennytm PTAL

[kennytm]

LGTM