Matching on empty strings, not nulls, in a MySQL column - mysql

Question

I can't get the right syntax - I'm trying to match on the column as an empty string, not a null. I've tried delimiting the string all number of ways, using single double quotes.
containerRefNo = "\"\"";
ps = getConnection().prepareStatement(
"delete from inumber_join where container_no = ?");
The error I receive is
You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'from inumber_join where container_no = '""''

Answer 1

When using a parameterized query you don't need to include any delimiters in the parameter value. Simply using ps.setString(1, ""); works fine for me.
That is, ...
// setup
try (Statement st = conn.createStatement()) {
st.executeUpdate(
"CREATE TEMPORARY TABLE inumber_join_temp (" +
"id INT AUTO_INCREMENT, " +
"container_no VARCHAR(10) NULL, " +
"PRIMARY KEY (id)" +
")");
st.executeUpdate(
"INSERT INTO inumber_join_temp (container_no) " +
"VALUES (null), (''), (null), (''), (null)");
}
// test
String sql =
"SELECT COUNT(*) AS n " +
"FROM inumber_join_temp " +
"WHERE container_no = ?";
try (PreparedStatement ps = conn.prepareStatement(sql)) {
ps.setString(1, ""); // search for empty string
try (ResultSet rs = ps.executeQuery()) {
rs.next();
System.out.println(rs.getInt(1));
}
}
... returns
2