If I run my Query in Oracle it is running without any error but when I run it inside C# gives ORA-00911: invalid character

Question

    using (OracleConnection conn1 = new OracleConnection(oradb1))
                        {

                            conn1.Open();

        using (OracleCommand crtCommand = new OracleCommand("WITH src 
     AS (SELECT src.table_name                src_table_name, 
                src.column_name               src_col_name, 
                src.data_type                 src_data_type, 
                src.data_length               src_data_len, 
                src.data_precision            src_data_precision, 
                src.data_scale                src_data_scale, 
                src.nullable                  src_nullable, 
                Decode(T.constraint_type, 'P', 'Primary Key', 
                                          'U', 'Unique', 
                                          '') AS src_cons 
         FROM   all_tab_columns src 
                left join (SELECT Cc.column_name, 
                                  Uc.constraint_type 
                           FROM   user_cons_columns cc, 
                                  user_constraints uc 
                           WHERE  Cc.constraint_name = Uc.constraint_name 
                                  AND Cc.table_name = Uc.table_name) t 
                       ON T.column_name = Src.column_name 
         WHERE  table_name = 'INSTRUCTOR' 
                AND owner = 'ERHAN'), 
     tgt 
     AS (SELECT tgt.table_name                tgt_table_name, 
                tgt.column_name               tgt_col_name, 
                tgt.data_type                 tgt_data_type, 
                tgt.data_length               tgt_data_len, 
                tgt.data_precision            tgt_data_precision, 
                tgt.data_scale                tgt_data_scale, 
                tgt.nullable                  tgt_nullable, 
                Decode(T.constraint_type, 'P', 'Primary Key', 
                                          'U', 'Unique', 
                                          '') AS tgt_cons 
         FROM   all_tab_columns tgt 
                left join (SELECT Cc.column_name, 
                                  Uc.constraint_type 
                           FROM   user_cons_columns cc, 
                                  user_constraints uc 
                           WHERE  Cc.constraint_name = Uc.constraint_name 
                                  AND Cc.table_name = Uc.table_name) t 
                       ON T.column_name = tgt.column_name 
         WHERE  table_name = 'INSTRUCTOR' 
                AND owner = 'SARIGUL'), 
     col_details 
     AS (SELECT src.src_table_name, 
                Nvl(tgt.tgt_table_name, First_value(tgt_table_name) 
                                          over( 
                                            ORDER BY tgt_table_name nulls last)) 
                   tgt_table_name, 
                src.src_col_name, 
                src.src_data_type, 
                src.src_data_len, 
                src.src_data_precision, 
                src.src_data_scale, 
                src.src_nullable, 
                src_cons, 
                tgt.tgt_col_name, 
                tgt.tgt_data_type, 
                tgt.tgt_data_len, 
                tgt.tgt_data_precision, 
                tgt.tgt_data_scale, 
                tgt.tgt_nullable, 
                tgt_cons 
         FROM   src 
                full outer join tgt 
                             ON ( src.src_col_name = tgt.tgt_col_name )) 
SELECT * 
FROM   (SELECT CASE 
                 WHEN tgt_data_type != src_data_type 
                       OR tgt_data_len != src_data_len 
                       OR tgt_data_precision != src_data_precision 
                       OR tgt_data_scale != src_data_scale 
                       OR tgt_nullable != src_nullable THEN 
                 'alter table ' 
                 || tgt_table_name 
                 || ' modify ' 
                 || tgt_col_name 
                 || ' ' 
                 || src_data_type 
                 || ' ' 
                 || CASE 
                      WHEN src_data_type IN 
                           ( 'DATE' 
                           ) THEN NULL 
                      ELSE 
                        CASE 
                          WHEN src_data_type 
                               IN ( 
                               'VARCHAR', 
                               'VARCHAR2' 
                               ) THEN ' (' 
                                      || 
                 Nvl(To_char(src_data_len), ' ') 
                                                                      || ') ' 
                 ELSE Decode(Nvl(src_data_precision, -1), -1, NULL, 
                      Nvl(To_char(src_data_precision), ' ') 
                      || ', ' 
                      || Nvl(To_char(src_data_scale), ' ') 
                      || ')') 
                                                                   END 
                                                               END 
                                                            || CASE 
                 WHEN tgt_nullable = 'Y' THEN ' null ' 
                 ELSE ' not null ' 
                                                               END 
                                                            || tgt_cons 
                 WHEN tgt_col_name IS NULL THEN 'alter table ' 
                                                || tgt_table_name 
                                                || ' add ' 
                                                || src_col_name 
                                                || ' ' 
                                                || ' ' 
                                                || ' ' 
                                                || src_data_type 
                                                || ' ' 
                                                || CASE 
                                                     WHEN src_data_type IN ( 
                                                          'DATE' ) 
                                                   THEN NULL 
                                                     ELSE 
                 CASE 
                   WHEN src_data_type IN ( 
                        'VARCHAR', 'VARCHAR2' )THEN 
                   '(' 
                   || 
                   Nvl(To_char(src_data_len), ' ') 
                   || 
                   ') ' 
                   ELSE Decode(Nvl(src_data_precision, -1 
                               ), -1, NULL, 
                        Nvl(To_char(src_data_precision), 
                        ' ') 
                        || ', ' 
                        || Nvl(To_char(src_data_scale), 
                           ' ') 
                        || ')') 
                 END 
                                                   END 
                                                || tgt_cons 
                 WHEN src_col_name IS NULL THEN 'alter table ' 
                                                || tgt_table_name 
                                                ||' drop ' 
                                                ||tgt_col_name 
               END alter_statement 
        FROM   col_details) 
WHERE  alter_statement IS NOT NULL; ", conn1))
                    {
                        richTextBox1.AppendText(Environment.NewLine);
                        richTextBox1.AppendText(crtCommand.ExecuteNonQuery().ToString());
                        richTextBox1.AppendText(Environment.NewLine);
                    }

                }

Answer 1

Remove the ";" semicolon at the end! OracleCommand automatically adds on at the end of your query string.