Category: Technical

CREATE TABLE secretData (
    secretValue int COMMENT 'If this goes over 5, WWIII will start'
);

CREATE SQL SECURITY DEFINER VIEW censoredData AS 
SELECT * FROM secretData WHERE secretValue < 5 WITH CHECK OPTION;

GRANT SELECT, INSERT ON test.censoredData TO 'evilFiend'@'%';

<telephone> ring ring

<sysadmin> "Hello?"

<evilFiend> "I'd like to create an insertable view on some tables I already have rights to. I don't know just yet what I'll use for my select statement."

<sysadmin> "Ok. I'll set it up so you can do what you'd like."

CREATE SQL SECURITY INVOKER VIEW evilFiendsView AS SELECT 1;
GRANT SELECT, INSERT, ALTER ON test.evilFiendsView TO 'evilFiend'@'%';

evilFiend connects to the server, while twiddling the end of his handlebar mustache.

ALTER VIEW evilFiendsView AS 
SELECT * FROM censoredData WITH LOCAL CHECK OPTION;

INSERT INTO evilFiendsView VALUES (42);

Muhahaha!

Time for another MySQL Community Quiz:

Everybody knows that LAST_INSERT_ID() returns the value most recently created in an auto_increment column. Fewer of us know that you can pass a value to LAST_INSERT_ID(), and that value will be returned for the next call to LAST_INSERT_ID(). For example,

INSERT INTO table (someNonAutoIncrementField) VALUES (LAST_INSERT_ID(42));
SELECT LAST_INSERT_ID();

The INSERT inserts ’42’ into the table, and the SELECT returns 42.

So, here’s the question: What if we pass an expression to LAST_INSERT_ID and also use an auto_increment field in the same statement?

CREATE TABLE test (id int auto_increment primary key, field int);
INSERT INTO test (id, field) VALUES (NULL, LAST_INSERT_ID(42));
SELECT LAST_INSERT_ID();

You get the auto_increment field, at least in this case:

mysql> INSERT INTO test (id, field) VALUES (NULL, LAST_INSERT_ID(42));
Query OK, 1 row affected (0.08 sec)

mysql> SELECT LAST_INSERT_ID();
+------------------+
| LAST_INSERT_ID() |
+------------------+
|                1 |
+------------------+
1 row in set (0.00 sec)

And for a follow up, does it matter if you swap the insertion around?

INSERT INTO test (field, id) VALUES (LAST_INSERT_ID(42), NULL);
SELECT LAST_INSERT_ID();

Nope.

mysql> INSERT INTO test (field, id) VALUES (LAST_INSERT_ID(42), NULL);
Query OK, 1 row affected (0.08 sec)

mysql> SELECT LAST_INSERT_ID();
+------------------+
| LAST_INSERT_ID() |
+------------------+
|                2 |
+------------------+
1 row in set (0.00 sec)

The manual warns about mixing LAST_INSERT_ID() and LAST_INSERT_ID(expr). This may fall under that same caveat.

First, the setup:

CREATE TABLE `user` (
  `user` varchar(255) DEFAULT NULL,
  `host` varchar(255) DEFAULT NULL,
  `sort` int(11) DEFAULT NULL
);

INSERT INTO `user` 
    (`user`, `host`, `sort`) 
VALUES 
    ('','%',8),
    ('testUser','%',7),
    ('','%localhost',9),
    ('testUser','%localhost',5),
    ('','%localhost%',10),
    ('testUser','%localhost%',6),
    ('','localhost',2),
    ('testUser','localhost',1),
    ('','localhost%',4),
    ('testUser','localhost%',3);

Now, the quiz:

SELECT * FROM user ORDER BY ___

Fill in the blank to get the following output. Difficulty: the `sort` field may not appear anywhere in the query.

+----------+-------------+------+
| user     | host        | sort |
+----------+-------------+------+
| testUser | localhost   |    1 |
|          | localhost   |    2 |
| testUser | localhost%  |    3 |
|          | localhost%  |    4 |
| testUser | %localhost  |    5 |
| testUser | %localhost% |    6 |
| testUser | %           |    7 |
|          | %           |    8 |
|          | %localhost  |    9 |
|          | %localhost% |   10 |
+----------+-------------+------+

Culled from the Certification Study Guide:

mysql> SELECT * FROM test;
+----------------+
| data           |
+----------------+
| This is a test |
+----------------+
1 row in set (0.00 sec)

mysql> SELECT UPPER(data) FROM test;
+----------------+
| UPPER(data)    |
+----------------+
| This is a test |
+----------------+
1 row in set (0.03 sec)

How’s that work?

 CREATE TABLE `test` (
   `data` varbinary(255) default NULL
 );

Binary strings are just a list of bytes. They aren’t characters anymore, so there is no upper or lower case. Remember that when choosing between char/varchar/text and binary/varbinary/blob.