title: error in making Foreign Key Constraints by Workbench
body: <p>I made database consists of two columns in MySQL Workbrench. I imported data from .csv to sql. The sctructures of columns are:
  for table 'gases'</p>
  <pre><code>CREATE TABLE `gases` (
    `site_gaw_id` text,
    `year` int(11) DEFAULT NULL,
    `month` int(11) DEFAULT NULL,
    `day` int(11) DEFAULT NULL,
    `value` double DEFAULT NULL,
    `ID_station` int(11) NOT NULL,
    `name_of_value` text,
    KEY `ID_station` (`ID_station`)
  ) ENGINE=InnoDB DEFAULT CHARSET=latin1
  </code></pre>
  <p>for table stations_2</p>
  <pre><code>CREATE TABLE `stations_2` (
    `ID_stations` int(11) NOT NULL,
    `Name` text,
    `Type` text,
    `Country` text,
    `Latitude` double DEFAULT NULL,
    `Longitude` double DEFAULT NULL,
    `elevation` int(11) DEFAULT NULL,
    `site_gaw_id` text,
    `stations_id` int(11) DEFAULT NULL,
    PRIMARY KEY (`ID_stations`)
  ) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
  </code></pre>
  <p>I want to make relations in workbrench between two columns.The relation should be by  by &quot;ID_station&quot;.</p>
  <p>So I need to make Foreign Key Constraints. In workbrench I write:</p>
  <pre><code>ALTER TABLE `gases_db`.`gases` 
  ADD CONSTRAINT `id_station_fk`
    FOREIGN KEY (`ID_station`)
    REFERENCES `gases_db`.`stations_2` (`ID_stations`)
    ON DELETE CASCADE
    ON UPDATE CASCADE;
  </code></pre>
  <p>And as the result I got an error:</p>
  <pre><code>Operation failed: There was an error while applying the SQL script to the database.
  ERROR 1452: Cannot add or update a child row: a foreign key constraint fails (`gases_db`.`#sql-3b5_a`, CONSTRAINT `id_station_fk` FOREIGN KEY (`ID_station`) REFERENCES `stations_2` (`ID_stations`) ON DELETE CASCADE ON UPDATE CASCADE)
  SQL Statement:
  </code></pre>
  <p>How should I solve my problem?</p>