When numbering is allowed you can label each row individually. The LaTeX commands to format a formula as a display differ from the commands to format an inline formula only in the choice of the delimiters that identify mathematics mode. Adding a star after the environment name is a common idiom in LaTeX which means dont number these and can be used for sections and so forth as well.
Here we arrange the equations in three columns.
Xian -- putting the label before the align might change the position of the equation number but it will also give an incorrect value with eqref. Xian -- putting the label before the align might change the position of the equation number but it will also give an incorrect value with eqref. The equation number is moved next to the equation which is not the intended behavior. By default equation numbers are place on the right side of an equation for any numbered math environment such as equation eqnarray and align.