feat: substitute __NOW__ to current timestamp in nanoseconds (#220)

Co-authored-by: xxchan <xxchan22f@gmail.com>

CHANGELOG.md

@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+**Breaking changes**:
 * runner: `RecordOutput` is now returned by `Runner::run` (or `Runner::run_async`). This allows users to access the output of each record, or check whether the record is skipped.
+* substitution: add a special variable `__NOW__` which will be replaced with the current Unix timestamp in nanoseconds.
 
 ## [0.20.6] - 2024-06-21
 

sqllogictest/src/substitution.rs

@@ -23,6 +23,13 @@ impl<'a> subst::VariableMap<'a> for Substitution {
                 test_dir.path().to_string_lossy().into_owned().into()
             }
 
+            "__NOW__" => std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .expect("failed to get current time")
+                .as_nanos()
+                .to_string()
+                .into(),
+
             key => Env.get(key),
         }
     }

tests/substitution/basic.slt

@@ -25,6 +25,10 @@ echo "$MY_USERNAME"
 statement ok
 path $__TEST_DIR__
 
+# a special variable `__NOW__` to get the current timestamp in nanoseconds
+statement ok
+time $__NOW__
+
 # non existent variables without default values are errors
 statement error No such variable
 check $NONEXISTENT_VARIABLE

tests/substitution/substitution.rs

@@ -37,6 +37,10 @@ impl sqllogictest::DB for FakeDB {
                     x.to_string()
                 }
             }
+            Some(("time", x)) => {
+                let _ = x.parse::<u128>().map_err(|_| FakeDBError)?;
+                x.to_string()
+            }
             _ => return Err(FakeDBError),
         };