text: Q:
  
  Change SQL Field Data Type varchar to float with data already stored
  
  I have an imported database which contain lots of float field.
  When I imported it, all the float field converted to string and I need to convert it back.
  I try alter table to change the data type but I keep getting error (even if the row is empty or null).
  EDIT : The server is curently down so I can't get the error message at the moment. My DBMS is SQL Server.
  
  A:
  
  you can do so if all data are really numeric type.
  There may be some data which hv null --no problem here.
  There may be some data which are blank(('') but not null--problem is because of this.
  First you make a select query to retrieve all data which are blank
  say,
  Select * from table1 where col=''
  now update these rows with null
  update table1 set col=null where col=''
  After this,I think you can easily convert it to float 
  References: error converting data type varchar column to float.
  
  