Interview question

What is the difference between execute(), executeQuery(), and executeUpdate() in JDBC? JDBC में execute(), executeQuery(), और executeUpdate() में क्या अंतर है?

Answer

Method	Used for	Return type
executeQuery()	SELECT statements only	ResultSet
executeUpdate()	INSERT, UPDATE, DELETE, DDL statements	int (number of rows affected)
execute()	Any SQL statement, when the type is unknown beforehand	boolean (true if result is a ResultSet)

Statement stmt = conn.createStatement();

// executeQuery() - for SELECT, returns rows
ResultSet rs = stmt.executeQuery('SELECT * FROM users');
while (rs.next()) {
    System.out.println(rs.getString('name'));
}

// executeUpdate() - for INSERT/UPDATE/DELETE, returns affected row count
int rowsInserted = stmt.executeUpdate(
    "INSERT INTO users (name, email) VALUES ('John', 'john@example.com')");
System.out.println(rowsInserted + ' row(s) inserted');

int rowsUpdated = stmt.executeUpdate(
    "UPDATE users SET name = 'Jane' WHERE id = 1");
System.out.println(rowsUpdated + ' row(s) updated');

// execute() - generic, used when statement type isn't known ahead of time
boolean isResultSet = stmt.execute('SELECT * FROM users');
if (isResultSet) {
    ResultSet result = stmt.getResultSet();
} else {
    int updateCount = stmt.getUpdateCount();
}

// Using execute() for statements that could be either (e.g. stored procedures)
boolean hasResults = stmt.execute('{call processOrder(1)}');

// Common mistake: using executeQuery() for an INSERT statement
// stmt.executeQuery('INSERT INTO users ...');  // SQLException: not a SELECT

Method	किसके लिए	Return type
executeQuery()	सिर्फ SELECT	ResultSet
executeUpdate()	INSERT, UPDATE, DELETE, DDL	int (affected rows)
execute()	कोई भी SQL, type अनजान होने पर	boolean

Statement stmt = conn.createStatement();

ResultSet rs = stmt.executeQuery('SELECT * FROM users');
while (rs.next()) {
    System.out.println(rs.getString('name'));
}

int rowsInserted = stmt.executeUpdate(
    "INSERT INTO users (name, email) VALUES ('John', 'john@example.com')");
System.out.println(rowsInserted + ' row(s) inserted');

int rowsUpdated = stmt.executeUpdate(
    "UPDATE users SET name = 'Jane' WHERE id = 1");

boolean isResultSet = stmt.execute('SELECT * FROM users');
if (isResultSet) {
    ResultSet result = stmt.getResultSet();
} else {
    int updateCount = stmt.getUpdateCount();
}

// गलती: INSERT के लिए executeQuery() use करना
// stmt.executeQuery('INSERT INTO users ...');  // SQLException

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