create count opcode

core/vdbe/execute.rs

@@ -4749,6 +4749,17 @@ pub fn op_affinity(
     Ok(InsnFunctionStepResult::Step)
 }
 
+pub fn op_count(
+    program: &Program,
+    state: &mut ProgramState,
+    insn: &Insn,
+    pager: &Rc<Pager>,
+    mv_store: Option<&Rc<MvStore>>,
+) -> Result<InsnFunctionStepResult> {
+    state.pc += 1;
+    Ok(InsnFunctionStepResult::Step)
+}
+
 fn exec_lower(reg: &OwnedValue) -> Option<OwnedValue> {
     match reg {
         OwnedValue::Text(t) => Some(OwnedValue::build_text(&t.as_str().to_lowercase())),

core/vdbe/explain.rs

@@ -1448,6 +1448,19 @@ pub fn insn_to_str(
                         .join(", ")
                 ),
             ),
+            Insn::Count {
+                cursor_id,
+                target_reg,
+                exact,
+            } => (
+                "Count",
+                *cursor_id as i32,
+                *target_reg as i32,
+                if *exact { 0 } else { 1 },
+                OwnedValue::build_text(""),
+                0,
+                "".to_string(),
+            ),
         };
     format!(
         "{:<4}  {:<17}  {:<4}  {:<4}  {:<4}  {:<13}  {:<2}  {}",

core/vdbe/insn.rs

@@ -857,6 +857,16 @@ pub enum Insn {
         count: NonZeroUsize,
         affinities: String,
     },
+
+    /// Store the number of entries (an integer value) in the table or index opened by cursor P1 in register P2.
+    ///
+    /// If P3==0, then an exact count is obtained, which involves visiting every btree page of the table.
+    /// But if P3 is non-zero, an estimate is returned based on the current cursor position.
+    Count {
+        cursor_id: CursorID,
+        target_reg: usize,
+        exact: bool,
+    },
 }
 
 impl Insn {
@@ -977,6 +987,7 @@ impl Insn {
             Insn::NotFound { .. } => execute::op_not_found,
             Insn::Affinity { .. } => execute::op_affinity,
             Insn::IdxDelete { .. } => execute::op_idx_delete,
+            Insn::Count { .. } => execute::op_count,
         }
     }
 }