parser: support DELETE FROM ... AS ... syntax

[kennytm]

What problem does this PR solve?

Fix issue pingcap/tidb#11173. The DELETE FROM ... AS ... syntax was introduced in MySQL 8.0.16.

What is changed and how it works?

Recognize the new syntax in the parser.

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

• Need to update the documentation
  • May need to update https://pingcap.com/docs/v3.0/reference/sql/statements/delete/ if it is not auto-generated.

[kennytm]

(Integration test requires pingcap/tidb#11184 to pass)

[kennytm]

PTAL @tiancaiamao @shenli

[imtbkcat]

Hi kennytm, i try to run this SQL in MySQL 8.0, but failed.

mysql> DELETE FROM x t WHERE t.a = 4;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 't WHERE t.a = 4' at line 1

[kennytm]

@imtbkcat

https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-16.html

For consistency with the SQL standard and other RDBMS, table aliases are now supported in single-table as well as multi-table DELETE statements. (Bug #27455809)

[imtbkcat]

LGTM

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@ded7e04). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #383   +/-   ##
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  Coverage          ?   70.11%           
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  Files             ?       32           
  Lines             ?     7394           
  Branches          ?        0           
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  Hits              ?     5184           
  Misses            ?     1698           
  Partials          ?      512

Impacted Files	Coverage Δ
parser.go	70.58% <ø> (ø)

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[tangenta]

LGTM

[bb7133]

LGTM

[bb7133]

hi @kennytm , please update TiDB test case:

(write_test.go:1747: testSuite4.TestQualifiedDelete)

1767     _, err := tk.Exec("delete from t1 as a where a.c1 = 1")
1768     c.Assert(err, NotNil)