PostgreSQL query always return true

Question

I have query which must return a boolean but I always get the same result. I have tried this:

 boolean exist=stmt.execute("select exists(select 1 from calcul where 
 to_char(date, 'YYYY-MM')=to_char("+dates+", 'YYYY-MM') AND
 idproduit="+codeP+" AND ppa="+PPA+" AND tr="+TR+" AND net="+NET+" AND 
 dateper='"+datePer+"')");

The result is always true, never false; why?

the = sign is the assignment sign, while == is a comparison sign. — x6iae
– x6iae, Commented Nov 23, 2015 at 21:40
Please use a PreparedStatement, do not concatenate SQL queries like that. You also need to use executeQuery() as clearly documented in the JavaDocs — user330315
– user330315, Commented Nov 23, 2015 at 22:17

Keppil · Accepted Answer · 2015-11-23 21:37:58Z

2

The true just means that there is a result, as stated in the javadoc of execute():

Returns:
true if the first result is a ResultSet object; false if the first result is an update count or there is no result.

You need to call getResultSet() to get the actual result.

answered Nov 23, 2015 at 21:37

Keppil

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MadProgrammer · Accepted Answer · 2015-11-23 21:44:13Z

Take a look at the JavaDocs for Statement#execute(String)

Returns:
true if the first result is a ResultSet object; false if it is an update count or there are no results

You could use Statement#executeQuery(String) which will return a ResultSet, from which you will then need to inspect the result of the first row

Something like...

try (Statement stmt = con.createStatement()) {
    try (ResultSet rs = stmt.executeQuery("select exists(select 1 from calcul where to_char(date, 'YYYY-MM')=to_char("+dates+", 'YYYY-MM') AND idproduit="+codeP+" AND ppa="+PPA+" AND tr="+TR+" AND net="+NET+" AND dateper='"+datePer+"')")) {
        if (rs.next()) {
            boolean exists = rs.getBoolean(1);
        }
    }
} catch (SQLException exp) {
    exp.printStackTrace();
}

for example.

Having said that, I'd strongly encourage you to use a PreparedStatement, see Using Prepared Statements for more details

For example...

try (PreparedStatement stmt = con.prepareStatement("select exists(select 1 from calcul where to_char(date, 'YYYY-MM')=to_char(?, 'YYYY-MM') AND idproduit=? AND ppa=? AND tr=? AND net=? AND dateper='?')")) {
    stmt.setString(1, dates);
    stmt.setString(2, codeP);
    stmt.setString(3, PPA);
    stmt.setString(4, TR);
    stmt.setString(5, NET);
    stmt.setString(6, datePer);
    try (ResultSet rs = stmt.executeQuery()) {
        if (rs.next()) {
            boolean exists = rs.getBoolean(1);
        }
    }
} catch (SQLException exp) {
    exp.printStackTrace();
}

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