Merge Tables

Merge tables are sort of an earlier, simpler kind of partitioning with different restrictions and fewer optimizations. Whereas partitioning enforces the abstraction rigorously, denying access to the underlying partitions and permitting you to reference only the partitioned table, merge tables let you access the underlying tables separately from the merge table. And whereas partitioning is more integrated with the query optimizer and is the way of the future, merge tables are quasi-deprecated and might even be removed someday.

Like partitioned tables, merge tables are wrappers around underlying MyISAM tables with the same structure. Although you can think of merge tables as an older, more limited version of partitioning, they actually provide some features you can’t get with partitions.^[94]