Increase in salary during study leave?

There is no statutory right to a pay rise, instead the following applies:

In the absence of a collective agreement, the right to an annual salary review must be set out in the employment contract.
If your workplace is covered by a collective agreement, employees are entitled to an annual pay review. For salaried employees, there is rarely a minimum salary increase, instead individual salary setting is usually applied according to specific salary criteria.
If there is an employer-issued policy in force at the time, which provides for the right to an annual salary review, the policy must be complied with as long as it is in force.

If you have been on study leave for the entire period, you usually do not receive any salary increase regardless of whether you have an agreed salary review or not. This is partly because the leave was self-imposed, and partly because you did not perform anything for the employer during the period. If you worked part of the period, the situation may be different.

Note that the employer has no obligation to take inflation into account, unless the employer is bound by an agreement that specifies such an obligation.