Question

There is a good way to use a prepared statement in java where there is the possibility to have a probability that some parameter can be or not be set?

Let’s assume I have a complete query like this one:

SELECT * FROM Table1 WHERE Field1='....' AND Field2='....' AND Field3='....'

Then in my program I would like to do something like that (I know it’s not possible the way I write)

// part of code where I have 3 variable set by some logic and the query itself
//.........

String Query = "SELECT * FROM Table1 WHERE Field1=? ";
PreparedStatement s = conn.prepareStatement();          
s.setString(1, Field1Var);

if (Field2Var != Value)
{
    Query += " AND Field2=? ";
    s.setString(2, Field2Var);
}

if (Field3Var != Value3)
{
    Query += " AND Field3=? ";
    s.setString(3, Field3Var);
}
s = conn.prepareStatement(query);   

How can I achieve it without write many different queries?

Answer 1

String query = "SELECT * FROM Table1 WHERE 1=1";

if (Field1Var != Value1) {
    query += " AND Field1 = ? ";
}

if (Field2Var != Value2) {
    query += " AND Field2 = ? ";
}

if (Field3Var != Value3) {
    query += " AND Field3 = ? ";
}

PreparedStatement s = conn.prepareStatement(query); 

int i = 0;

if (Field1Var != Value1) {
    s.setString(++i, Field1Var);
}

if (Field2Var != Value2) {
    s.setString(++i, Field2Var);
}

if (Field3Var != Value3) {
    s.setString(++i, Field3Var);
}

1. Use an additional condition 1=1.
2. Use a counter variable.

Or you can write a “NamedPreparedStatement” like I did. (https://gist.github.com/1978317)