MySQL Judge field value to determine whether to insert a new record

Today, there is a new requirement to ensure that duplicate records are not inserted in a single table.

That is, ensure that the value of a field in each record is not duplicated.

Here is the SQL statement I gave:

 //  insert  into  select   Insert the value 1, insert the value 2, insert the value 3  from   DUAL  where  not  Span style= "COLOR:RGB (128, 128, 128); >exists   select  Span style= "COLOR:RGB (128, 128, 128); >*  where  The name of the table. Field 3 =  Insert value 3 
 )  

If the table. Verify field '! = ' parameter, a new record is inserted.

Reference documents:

The MySQL record does not exist when the insert record exists then the update implementation method

How can I tell if duplicate data for a specified field is not inserted in MySQL? (four methods of the post, the test found are not available or bad use.) )