/// <summary>
/// Generates SQL for this constraint.
/// </summary>
/// <param name="dialect"></param>
/// <param name="constraintName">the name of this constraint</param>
/// <returns>an SQL string</returns>
protected override String DoToSqlConstraint(Dialect dialect, String constraintName)
{
StringBuilder sb = StringHelper.CreateBuilder().Append(dialect.GetAddUniqueKeyConstraintString(constraintName))
.Append("(");
Boolean hadNullableColumn = AppendColumns(sb, dialect);
//do not add unique constraint on DB not supporting unique and nullable columns
return (!hadNullableColumn || dialect.SupportsNullableUnique) ?
sb.Append(")").ToString() :
null;
}
