if statement in JSTL

Use enhanced if condition it will be more easy

You don't need to do the zero/one bit, if you aren't using the ${sex} variable anywhere else other than your sql:query. Your problem can collapse from:

<c:set var="sex" value="${param.sex}"/><c:if test="$(param.sex=='male')" >    //set the sex to zero</c:if><c:if test="$(param.sex=='female')" >   //set the sex to one</c:if>...<sql:query dataSource="${dbcon}" var="result">    select firstname,lastname from members where sex = ?    <sql:param value="${sex}"></sql:param>

Down to just this:

<sql:query dataSource="${dbcon}" var="result">    select firstname,lastname from members where sex = ?    <sql:param value="${param.sex == 'male' ? 0 : 1}"></sql:param>

The point being that you can use param.sex directly in the sql:query statement, and you can use the "ternary operator" instead of using an if statement in this situation.

Google for more on the "JSTL ternary operator" or take a look here (scroll down to Ternary Operations): http://davidensinger.com/2014/07/fun-with-jstl-in-jsps/

UPDATE

To see the ternary operator in action and make sure the param.sex value is the value you expect you can just type this:

${param.sex == 'male' ? 0 : 1}

On a blank line and it should print either a 0 or 1 to your screen.

select firstname,lastname from members where sex =<%= Enter variable name assumed for sex in this EL %>