executor, infoschema: fix display of default CURRENT_TIMESTAMP with decimal

[bb7133]

What problem does this PR solve?

This PR fixes the following scenarios in which decimal fraction is missed for default CURRENT_TIMESTAMP in TiDB:

tidb> create table t(a datetime(3) default current_timestamp(3), b timestamp(4) default current_timestamp(4));
Query OK, 0 rows affected (0.01 sec)

• For SHOW CREATE TABLE:

tidb> show create table t;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                   |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t     | CREATE TABLE `t` (
  `a` datetime(3) DEFAULT CURRENT_TIMESTAMP,
  `b` timestamp(4) DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

• For SHOW (FULL) COLUMNS:

tidb> show full columns from t;
+-------+--------------+-----------+------+------+-------------------+-------+---------------------------------+---------+
| Field | Type         | Collation | Null | Key  | Default           | Extra | Privileges                      | Comment |
+-------+--------------+-----------+------+------+-------------------+-------+---------------------------------+---------+
| a     | datetime(3)  | NULL      | YES  |      | CURRENT_TIMESTAMP |       | select,insert,update,references |         |
| b     | timestamp(4) | NULL      | YES  |      | CURRENT_TIMESTAMP |       | select,insert,update,references |         |
+-------+--------------+-----------+------+------+-------------------+-------+---------------------------------+---------+
2 rows in set (0.01 sec)

• For the queries on information_schema:

tidb> select column_name, column_default from information_schema.COLUMNS where table_schema="test" and table_name = "t" order by column_name;
+-------------+-------------------+
| column_name | column_default    |
+-------------+-------------------+
| a           | CURRENT_TIMESTAMP |
| b           | CURRENT_TIMESTAMP |
+-------------+-------------------+
2 rows in set (0.00 sec)

Notice that for all displays of the default values of time-related columns, the decimal fraction part is missed. This would cause some errors when users try to use those pieces of information, for example, create a table from SHOW CREATE TABLE:

tidb> CREATE TABLE `t` (
  `a` datetime(3) DEFAULT CURRENT_TIMESTAMP,
  `b` timestamp(4) DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;
ERROR 1067 (42000): Invalid default value for 'a'

What is changed and how it works?

Simply adding the missed parts.

Check List

Tests

• Unit test
• Integration test

Code changes

• Has interface methods change

Side effects

• Increased code complexity

Related changes

• Need to cherry-pick to the release branch

[winkyao]

LGTM

[winkyao]

/rebuild

[tangenta]

LGTM

[codecov]

Codecov Report

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The diff coverage is n/a.

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[crazycs520]

LGTM

[bb7133]

/run-all-tests

[bb7133]

/run-integration-common-test