There's this challenge from portswigger: https://portswigger.net/web-security/sql-injection/blind/lab-time-delays

I noticed that these 2 solutions work: ' || pg_sleep(10)-- , ' || (SELECT pg_sleep(10)--

But this doesn't: ' || SELECT pg_sleep(10)--

And my question is what's the different between with and without () ?

CodePudding user response：

Because This is the syntax of the SQL:

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