sql: rewind txn sequence number in internal executor

If the internal executor is used by a user-initiated query, then it
shares the same transaction as the user's query. In that case, it's
important to step back the sequence number so that a single statement
does not read its own writes.

Release note: None

Author: rafiss

pkg/sql/conn_executor_exec.go

@@ -961,7 +961,18 @@ func (ex *connExecutor) execStmtInOpenState(
 	// single/common function. That would be where the stepping mode
 	// gets enabled once for all SQL statements executed "underneath".
 	prevSteppingMode := ex.state.mu.txn.ConfigureStepping(ctx, kv.SteppingEnabled)
-	defer func() { _ = ex.state.mu.txn.ConfigureStepping(ctx, prevSteppingMode) }()
+	prevSeqNum := ex.state.mu.txn.GetReadSeqNum()
+	defer func() {
+		_ = ex.state.mu.txn.ConfigureStepping(ctx, prevSteppingMode)
+
+		// If this is an internal executor that is running on behalf of an outer
+		// txn, then we need to step back the txn so that the outer executor uses
+		// the proper sequence number.
+		if ex.executorType == executorTypeInternal && ex.extraTxnState.fromOuterTxn {
+			err := ex.state.mu.txn.SetReadSeqNum(prevSeqNum)
+			retEv, retPayload, retErr = makeErrEvent(err)
+		}
+	}()
 
 	// Then we create a sequencing point.
 	//

pkg/sql/conn_executor_test.go

@@ -450,6 +450,8 @@ SELECT IF(x::INT::FLOAT = x,
              'NOOPE', 'insert saw its own writes: ' || x::STRING || ' (it is halloween today)')::FLOAT)
        + 0.1
   FROM t.test
+  -- the function used here is implemented by using the internal executor.
+  WHERE has_table_privilege('root', ((x+.1)/(x+1) + 1)::int::oid, 'INSERT') IS NULL
 `); err != nil {
 		t.Fatal(err)
 	}