Php/ MySql 'Advanced Search' Page

SELECT * FROM myTable WHERE field='$keyword';

SELECT * FROM myTable WHERE field LIKE '%$keyword%';//Let me know if this is the wrong approach

(field='$keywords') OR ($field='$keywords) (OR)....

<?php
$choice = $_POST['choice'];
$query = $_POST['query'];

if ($choice == "oneWord") {
    //Not 100% sure what you mean by one word but this is the simplest form
    //This assumes $query = a single word
    $result = mysql_query("SELECT * FROM table WHERE MATCH (field) AGAINST ('{$query}' IN BOOLEAN MODE)");
} elseif ($choice == "exactWords") {
    $result = mysql_query("SELECT * FROM table WHERE MATCH (field) AGAINST ('"{$query}"' IN BOOLEAN MODE)");
} elseif ($choice == "atLeastOneWord") {
    //The default with no operators if given multiple words will return rows that contains at least one of the words
    $result = mysql_query("SELECT * FROM table WHERE MATCH (field) AGAINST ('{$query}' IN BOOLEAN MODE)");
} elseif ($choice == "withoutTheTerm") {
    $result = mysql_query("SELECT * FROM table WHERE MATCH (field) AGAINST ('-{$query}' IN BOOLEAN MODE)");
}
?>

SELECT * FROM myTable WHERE field LIKE '%$keyword%'
or field LIKE '%$keyword2%'
or field LIKE '%$keyword3%';

SELECT * FROM myTable WHERE field NOT LIKE '%$keyword%';