仅在Golang表中不可用的情况下才插入元组？

In my use case, I want to write a function to insert a row in a table in Golang if the row is not available already. I am using MySql and github.com/go-sql-driver/mysql. I am getting an error while I try to insert through this function. But I am able to insert by running through the MySql console. Here is the function definition,

    func AddTag(t *objects.Tag) {

    //Get connection object
    db, err := GetDBConnection()
    defer db.Close()

    // Prepare statement for inserting data
    stmtIns, err := db.Prepare("INSERT INTO tag (tag_id, tag_name, metatag_id) SELECT * FROM (SELECT NULL, ?, ?) AS tmp WHERE NOT EXISTS ( SELECT tag_name FROM tag WHERE tag_name = ? ) LIMIT 1")
    if err != nil {
        fmt.Println("FATAL  ", time.Now(), "Error in prepare statement for Tag insert ")
        panic(err.Error()) 
    }

    defer stmtIns.Close()                         // Close the statement when we leave main() / the program terminates
    _, err = stmtIns.Exec(t.TagName, t.MetaTagId, t.TagName) // Insert tuples

    if err != nil {
        fmt.Println("FATAL  ", time.Now(), "Error in insert to Tag ")
        panic(err.Error()) 
    }

  }

Edit 1 : I am getting the following error,

FATAL    2015-06-14 17:13:15.631487042 -0700 PDT Error in insert to Tag
panic: Error 1136: Column count doesn't match value count at row 1

goroutine 1 [running]:
main.AddTag(0x1112e1a0, 0x0, 0x0)

Could anyone help me on this? Thank you

"Column count doesn't match value count" means that you didn't provide a value for a column in the table which doesn't have a default value.

Check your table schema (DESCRIBE tag;) and ensure that you are providing values for the other columns, or that they have a default value.