Add create view support

[AndrewDi]

What problem does this PR solve?

Implement view support, support following grammar:

1. create or replace view as SelectStmt ...
2. drop table ...
3. show full tables
4. show create table viewname
5. select from view

issue ref #7974
Part of the code reference from #4874

What is changed and how it works?

Use tableinfo to store view select statement

Check List

Tests

• Unit test

Code changes

• Has interface methods change
  Add CreateView interface to ddl/ddl.go
• Has persistent data change

Side effects

Related changes

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This change is 

[sre-bot]

Hi contributor, thanks for your PR.

This patch needs to be approved by someone of admins. They should reply with "/ok-to-test" to accept this PR for running test automatically.

[ngaut]

Well done.

[AndrewDi]

Do some commit clean...

[XuHuaiyu]

@AndrewDi will file a proposal for the details of supporting View these days.

[zz-jason]

please reorg the import packages.

[AndrewDi]

I will implement this feature with independent PRs.

[morgo]

How is the SQL mode handled with views - I assume it is dependent on the session executing the view?

(The MySQL compatible behavior is to capture the SQL mode when the view is created.)

[XuHuaiyu]

@morgo
Yes, we need to take SQL_MODE into consideration.

A minor case of view in MySQL, it seems that everything is frozen after CREATE_VIEW:

mysql> create view v as select "a" from t;
Query OK, 0 rows affected (0.03 sec)

mysql> select "a" from t;
+---+
| a |
+---+
| a |
+---+
1 row in set (0.00 sec)

mysql> select * from v;
+---+
| a |
+---+
| a |
+---+
1 row in set (0.00 sec)

mysql> set @@sql_mode='ANSI_QUOTES';                                                Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> select "a" from t
    -> ;
+------+
| a    |
+------+
| NULL |
+------+
1 row in set (0.00 sec)

mysql> select * from v;
+---+
| a |
+---+
| a |
+---+
1 row in set (0.00 sec)

[XuHuaiyu]

@morgo
We decided to implement the most basic features of view in TiDB,
as the task with P1 priority mentioned in this proposal #8416.

SQL_MODE in view may be listed as a P2 or P3 priority task.