Difference between SQLExec and SelectSQL in PeopleSoft

The general commands that we use to select data through People Code are
1. SQL Exec - To select different values of a single row.
2. Select SQL - To select multiple values of multiple rows.

1. SQL Exec Syntax 
SQLExec("select distinct EMPLID,ACAD_PROG from PS_ACAD_PROG where emplid = :1", "20163-19955", "20066", &getEmplidID,&getAcadProg); 
2. Select SQL Syntax

Local SQL &GRD_SQL;
Local Rowset &GRD_RS;
Local Record &rec;
Local Rowset &rsGrid, &rsDataSource;

&GRD_RS.Flush();
 &sSQLWhere = "acad_career = 'UGRD'";
&GRD_SQL = CreateSQL("select distinct emplid , phone from ps_hon_no_vw  where " | &sSQLWhere | "");

  While &GRD_SQL.Fetch(&emplid, &phone_nbr)
        
         &GRD_RS(1).PHN_NO_WRK.EMPLID.Value = &emplid;
        
         &GRD_RS(1).PHN_NO_WRK.PHONE.Value = &phone_nbr;
        
         &GRD_RS.InsertRow(0);
      End-While;
      &GRD_RS.DeleteRow(1);
      &GRD_SQL.Close();
   End-If;