PostgreSQL:pg_sleep 的串联

PostgreSQL: concatenation of pg_sleep

来自 portswigger 的挑战:https://portswigger.net/web-security/sql-injection/blind/lab-time-delays

我注意到这两个解决方案有效: ' || pg_sleep(10)-- , ' || (SELECT pg_sleep(10)--

但这不是:' || SELECT pg_sleep(10)--

我的问题是有和没有 () 有什么区别?

Because 这是SQL的语法:

A scalar subquery is an ordinary SELECT query in parentheses that returns exactly one row with one column.