Re: Duplicate values being created

[Robert Summerfield]

Sorry my miss understanding of concurrency. Is there not logic in my table set-up to prevent values from other sources/tables from influencing the outcome? postId in my posts table is set to auto_increment and is the pk therefore must be unique. postId in my images tables is defined as a foreign key and is referenced to the parent table.
The image stable may have many rows with an display order of for example 2 but each one of them would have a unique postId value, this seems logical. So given the above structure, how could SELECT display_order FROM ext_images WHERE parentId = XX ORDER BY display_order DESC LIMIT 1 possibly not return the highest value? I can't understand where the logic could break down.