Query runs in MySql workbench but not in Java eclipse

Question

I have created a query that is working properly in MySQL workbench but when i run it in eclipse is not working. Connection with database is working properly because with simpler queries I had correct results.

java code:

                String queryAlter = "SELECT count(*) ";
                queryAlter += "INTO @exist ";
                queryAlter += "FROM information_schema.columns ";
                queryAlter += "WHERE table_schema = database() ";
                queryAlter += "and COLUMN_NAME = 'question" + (100 + number + 1)+"' ";
                queryAlter += "AND table_name = '"+ tableName+"'; ";

                queryAlter += "set @query = IF(@exist <= 0, 'alter table "+ tableName+" add column question" + (100 + number + 1)+" varchar(2048) NULL', ";
                queryAlter += "'select \\'Column Exists\\' status'); ";
                queryAlter += "use joomla30; ";
                queryAlter += "prepare stmt from @query; ";

                queryAlter += "EXECUTE stmt;";

and I get this message:

An error occurred. Maybe user/password is invalid com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'set @query = IF(@exist <= 0, 'alter table n0x3c_twoquestions_table add column qu' at line 1

also the string of query is:

 SELECT count(*) INTO @exist FROM information_schema.columns WHERE table_schema = database() and COLUMN_NAME = 'question101' AND table_name = 'n0x3c_twoquestions_table'; set @query = IF(@exist <= 0, 'alter table n0x3c_twoquestions_table add column question101 varchar(2048) NULL', 'select \'Column Exists\' status'); use joomla30; prepare stmt from @query; EXECUTE stmt;

I also tried this in java that I have read from MySQL Query works in PhpMyAdmin but not in JAVA Eclipse :

                String s1 = "SELECT count(*) INTO @exist FROM information_schema.columns WHERE table_schema = database() and COLUMN_NAME = 'question" + (100 + number + 1)+"' AND table_name = '"+ tableName+"'; ";

                String s2 = "set @query = IF(@exist <= 0, 'alter table "+ tableName+" add column question" + (100 + number + 1)+" varchar(2048) NULL', 'select \\'Column Exists\\' status'); ";
                String s3 = "use joomla30; ";
                String s4 = "prepare stmt from @query; ";

                stmt.addBatch(s1);
                stmt.addBatch(s2);    
                stmt.addBatch(s3);   
                stmt.addBatch(s4);

                stmt.executeBatch();
                conn1.commit();

but I have this error:

java.sql.BatchUpdateException: Can not issue SELECT via executeUpdate().

Answer 1

You can use two different queries.

The first is to check the existence of the column:

String countQuery = "select count(*) from information_schema.columns WHERE table_schema = database() and COLUMN_NAME = 'question106' and table_name='n0x3c_twoquestions_table'";

Then if countQuery returns 0, you can execute the alterQuery:

String alterQuery = "alter table n0x3c_twoquestions_table add column question106 varchar(2048) NULL";

If you don't want to use two differents queries, you can handle this with exception catching:

String alterQuery = "alter table n0x3c_twoquestions_table add column question106 varchar(2048) NULL";
try (Connection conn = ds.getConnection(); PreparedStatement ps = conn.prepareStatement(alterQuery)) {
    ps.execute();
} catch (SQLException e) {
    if (e.getErrorCode() == 1060) {
        columnExists = true;
    } else {
        // TODO handle exception
    }
}

I found the error code MySQL Server error codes.