I need the metadata from a mysql resultset, is this possible? - mysql

Question

I'd like to obtain the metadata from the results of a mysql query so I can put it into a datatable in c#. I primarily need the column name and the data type. Here's a simple example.
show columns from (
select sum(subtotal) as subtotal
, sum(tax1+tax2+tax3+tax4) as tax
, sum(subtotal)+sum(tax1+tax2+tax3+tax4) as total
from tbltransmaster
where batchnum in (
SELECT BatchNum
FROM tblshiftmaster
WHERE ClosingTS <> -1
ORDER BY OpeningTS ASC
)
) as x
It generates this error though
Error Code : 1064 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 '(
select sum(subtotal) as subtotal
, sum(tax1+tax2+tax3+tax4) as tax
, sum' at line 1
Could someone provide me with some advice, or perhaps a link to assist with this?

Answer 1

show columns only works for actual tables and views, not for queries.
Since you mention C#, you're probably using ADO.NET ? You can directly fill a DataTable which figure out the data types and column names.
DbConnection conn = null;
DbConnection conn = null;
DbCommand cmd = null;
DbDataAdapter da = null;
DataTable tbl = new DataTable();
conn = new MySqlConnection(connectionString);
conn.Open();
cmd = conn.CreateCommand();
cmd.CommandText = query;
da = new MySqlDataAdapter();
da.SelectCommand = cmd;
da.Fill(tbl);
If you want to get the colum names only, you could fetch the result using a DataReader instead:
DbDataReader dbReader = cmd.ExecuteReader();
for (int i = 0; i < dbReader.FieldCount; i++) {
Type colType = dbReader.GetFieldType(i);
String colName = dbReader.GetName(i);
}
DbDataReader also have the .GetSchemaTable() which returns a DataTable describing the metadata of the result.