INSERT a row only if @@hostname equals a certain value

Question

Is it possible to use a WHERE clause somehow (or any other way) in an INSERT query so it only works if the @@hostname variable is a certain value? For example:

INSERT INTO table_name
    (field_1, field_2)
VALUES
    ('foo', 'bar')
WHERE @@hostname = 'url.to.host.here';

Answer 1

Note: @@hostname is the MySQL hostname.

You can invalid a select query like this because the MySQL optimizer sees this as an impossible WHERE.

SELECT
   'field_1'
 , 'field_2'
FROM
  DUAL
WHERE 0;

MySQL has an INSERT INTO ... SELECT query so when you use:

INSERT INTO
   table_name (
     field_1
   , field_2
  )
  SELECT
      'field_1'
    , 'field_2'
   FROM
     DUAL
   WHERE 0

The INSERT INFO will not be executed.

When you use:

INSERT INTO
   table_name (
     field_1
   , field_2
  )
  SELECT
      'field_1'
    , 'field_2'
   FROM
     DUAL
   WHERE 1;

The INSERT INTO will be executed. See demo http://sqlfiddle.com/#!9/5623f/1

With the @@hostname check:

INSERT INTO
   table_name (
     field_1
   , field_2
  )
  SELECT
      'field_1'
    , 'field_2'
   FROM
     DUAL
   WHERE IF(
     @@hostname = 'ip-10-0-0-15'
     , 1
     , 0
   );

See demo http://sqlfiddle.com/#!9/d9081/4.

As a sidenote you can also use this to "support" CHECK (MySQL doesn't support CHECK with CREATE TABLE statement) on columns normally you need triggers to do this.

See demo http://sqlfiddle.com/#!9/9dfa2/1.