title: What is the AgensGraph syntax to specify a mandatory property constraint?
body: <p>AgensGraph Developer documentation at <a href="https://bitnine.net/documentations/developer-manual-en.html#introduction" rel="nofollow noreferrer">https://bitnine.net/documentations/developer-manual-en.html#introduction</a> says that the product "Supports Unique, Mandatory, Check constraints". The online help shows the syntax for creating a unique property constraint but not the syntax for a mandatory property constraint. Is such a constraint actually supported?</p>