Fix zero-datetime in statement result raises ArgumentError

[gentlawk]

A zero-datetime value ('0000-00-00 00:00:00') is returned nil by Client#query,
but raises ArgumentError by Statement#execute.

client.prepare("SELECT CAST('0000-00-00 00:00:00' AS DATETIME) as test").execute.first
#=>
        6: from /home/gentlawk/work/ruby/mysql2/lib/mysql2/statement.rb:6:in `execute'
        5: from /home/gentlawk/work/ruby/mysql2/lib/mysql2/statement.rb:6:in `handle_interrupt'
        4: from /home/gentlawk/work/ruby/mysql2/lib/mysql2/statement.rb:7:in `block in execute'
        3: from /home/gentlawk/work/ruby/mysql2/lib/mysql2/statement.rb:7:in `_execute'
        2: from /home/gentlawk/work/ruby/mysql2/lib/mysql2/statement.rb:7:in `each'
        1: from /home/gentlawk/work/ruby/mysql2/lib/mysql2/statement.rb:7:in `civil'
ArgumentError (invalid date)

I fixed Statement#execute to return nil correctly for zero-datetime.

[sodabrew]

It would be equivalent to move this up as } else if (seconds...) {, no need to indent the entire if block.

[sodabrew]

I didn't get this one into the 0.5.3 release, but I want to plan for whether to include it in the next release or not. If you'd be so kind as to make the requested change to the if block?

[gentlawk]

Thanks for your advice!
I fixed the indent of if block.

[kamipo]

Looks like there is no reason to change the permission 644 to 755.

[gentlawk]

Hmm... you are exactly.
I fixed these.

[sodabrew]

I am confused why MySQL doesn't return NULL as the value type in this case, and is instead giving back an all-zeroes date value. It seems like the fix is papering over some quirk here. That said, it does appear that there's "no such thing" as an all-zeroes DATETIME, so mapping that to NULL appears consistent with MySQL's own behavior.

Maybe the command-line client is actually doing this same paper-over?

Here's my local session output:

mysql> SELECT CAST('0000-00-00 00:00:00' AS DATETIME);
+-----------------------------------------+
| CAST('0000-00-00 00:00:00' AS DATETIME) |
+-----------------------------------------+
| NULL                                    |
+-----------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> SELECT CAST('0000-00-00 00:00:01' AS DATETIME);
+-----------------------------------------+
| CAST('0000-00-00 00:00:01' AS DATETIME) |
+-----------------------------------------+
| 0000-00-00 00:00:01                     |
+-----------------------------------------+
1 row in set (0.00 sec)

mysql> PREPARE t FROM 'SELECT CAST(? AS DATETIME)';
Query OK, 0 rows affected (0.01 sec)
Statement prepared

mysql> SET @a = '0000-00-00 00:00:00';
Query OK, 0 rows affected (0.01 sec)

mysql> SET @b = '0000-00-00 00:00:01';
Query OK, 0 rows affected (0.00 sec)

mysql> EXECUTE t USING @a;
+---------------------+
| CAST(? AS DATETIME) |
+---------------------+
| NULL                |
+---------------------+
1 row in set, 1 warning (0.01 sec)

mysql> EXECUTE t USING @b;
+---------------------+
| CAST(? AS DATETIME) |
+---------------------+
| 0000-00-00 00:00:01 |
+---------------------+
1 row in set (0.00 sec)

[sodabrew]

Thanks for taking the review feedback, the changes look good. I just want to make sure I understand this under the hood before landing the PR.

[gentlawk]

Possibly, would your MySQL be running with 'NO_ZERO_DATE' mode?
If sql_mode variable is 'NO_ZERO_DATE' MySQL returns NULL for '0000-00-00 00:00:00'.

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

mysql> SELECT CAST('0000-00-00 00:00:00' AS DATETIME);
+-----------------------------------------+
| CAST('0000-00-00 00:00:00' AS DATETIME) |
+-----------------------------------------+
| NULL                                    |
+-----------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> SELECT CAST('0000-00-00 00:00:01' AS DATETIME);
+-----------------------------------------+
| CAST('0000-00-00 00:00:01' AS DATETIME) |
+-----------------------------------------+
| 0000-00-00 00:00:01                     |
+-----------------------------------------+
1 row in set (0.00 sec)

mysql> SET @@sql_mode = '';
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT CAST('0000-00-00 00:00:00' AS DATETIME);
+-----------------------------------------+
| CAST('0000-00-00 00:00:00' AS DATETIME) |
+-----------------------------------------+
| 0000-00-00 00:00:00                     |
+-----------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT CAST('0000-00-00 00:00:01' AS DATETIME);
+-----------------------------------------+
| CAST('0000-00-00 00:00:01' AS DATETIME) |
+-----------------------------------------+
| 0000-00-00 00:00:01                     |
+-----------------------------------------+
1 row in set (0.00 sec)