I realize there is a simple non SQL solution, however this is a pure sql solution. It may not be as slow as you think. This is the case where you do not have column names in your input table SAS does ...

Transposing rows to columns using proc sql partitioning\n%let pgm=utl-transposing-rows-to-columns-using-proc-sql-partitioning; ...

Learn how to Transpose Row to Column in Excel. Transpose converts horizontal row data sheets into vertical column style sheets and back.