How to check select date in database

Note it is windows application. Database design as follows in Ms Access Staff Name Text Subject Text Day Text Records in the database as follows. Staff Leave Details (table name StaffLeaveDetails) Staff Name Subject Day Ram Eng Wednesday Sam Tam Tuesday Gopi Mat Friday Ram Eng Thursday Magesh Sci Friday Gopi Eng Saturday Another Database design as follows i Ms Access Table Name (Staff Availability) Staff Name Text Date Date Time In the Staff Availability above two fields are saving in the database. My Design Screen as follows. Staff Name Combo Box(in that combo box all staff name retrieved StaffLeaveDetails table and display in to the Combo Box) Desing Screen Staff Name Combobox Calendar (month Calendar) Date Textbox. When i select the Staff Name from the Combo box and select the Date from the calendar that selected date is display in the textbox. I want to check the selected Date exists for Partiuclar Staff Name in the StaffLeaveDetails table, if date exists show the message "Select Different Date". for that how can i validate.How can i do using csharp. please help me. Regards & Thanks, Narasiman P. Note it is windows application.