I have a database that is using AMM (Automatic Memory Management). MEMORY_TARGET and MEMORY_MAX_TARGET are set to 13Gb. The SGA_MAX_SIZE parameter is set to zero, but when the database starts, the SGA_MAX_SIZE parameter show me 13 Gb.
This is so, because according to the documentation;
When either MEMORY_TARGET or MEMORY_MAX_TARGET is specified the default value of SGA_MAX_SIZE is set to the larger of the two parameters.
In this case is the same value for the two parameter, 13 Gb.
HTH – Antonio NAVARRO