https://www.postgresql.org/message-id/CAM3SWZRP0c3g6+aJ=YYDGYAcTZg0xA8-1_FCVo5Xm7hrEL34kw@mail.gmail.com https://www.postgresql.org/message-id/CAM3SWZRP0c3g6+aJ

https://www.postgresql.org/message-id/CAM3SWZRP0c3g6+aJ=YYDGYAcTZg0xA8-1_FCVo5Xm7hrEL34kw@mail.gmail.com https://www.postgresql.org/message-id/CAM3SWZRP0c3g6+aJ=YYDG... upsert is built on top of insert while merge allows you specify multiple conditions and includes the ability to perform a delete. i.e if you have a blog post with a list of tags, you could say: - if submitted tag is not found > insert it - if submitted tag is found > do nothing - if tag exists that wasn't submitted > delete it It can be quite powerful but it can get difficult to read also. I just hate using it in SQL Server because every time someone adds it, a year later its the code causing deadlocks.