diff --git a/db/executor.go b/db/executor.go
index 6459f4e2..0947000d 100644
--- a/db/executor.go
+++ b/db/executor.go
@@ -165,7 +165,7 @@ func (e *executor) execute(ctx context.Context, ast *sql.Query) {
 			if err == nil {
 				res, err = e.operate(ctx, stm)
 			} else {
-				res, err = []interface{}{}, queryNotExecuted
+				res, err = []interface{}{}, errQueryNotExecuted
 			}
 
 			rsp = &Response{
diff --git a/db/fetch.go b/db/fetch.go
index 177bd4a6..43e71d42 100644
--- a/db/fetch.go
+++ b/db/fetch.go
@@ -279,11 +279,11 @@ func (e *executor) fetchPaths(ctx context.Context, doc *data.Doc, exprs ...sql.E
 		case sql.DOT:
 			return e.fetchPaths(ctx, doc, exprs...)
 		case sql.OEDGE:
-			return nil, featureNotImplemented
+			return nil, errFeatureNotImplemented
 		case sql.IEDGE:
-			return nil, featureNotImplemented
+			return nil, errFeatureNotImplemented
 		case sql.BEDGE:
-			return nil, featureNotImplemented
+			return nil, errFeatureNotImplemented
 		}
 	case *sql.PartExpression:
 		switch val := val.Part.(type) {
diff --git a/db/table.go b/db/table.go
index 3af792cc..9f3b98d2 100644
--- a/db/table.go
+++ b/db/table.go
@@ -61,7 +61,7 @@ func (d *document) table(ctx context.Context, when method) (err error) {
 				// If there are GROUP BY clauses then
 				// let's calculate the
 
-				return featureNotImplemented
+				return errFeatureNotImplemented
 
 				ats := make([]interface{}, len(ft.Group))
 
diff --git a/db/vars.go b/db/vars.go
index f52bd360..5b2f1a85 100644
--- a/db/vars.go
+++ b/db/vars.go
@@ -63,9 +63,31 @@ const (
 )
 
 var (
-	workerCount           = runtime.NumCPU() * 2
-	queryNotExecuted      = errors.New("Query not executed")
-	queryIdentFailed      = errors.New("Found ident but no doc available")
-	featureNotImplemented = errors.New("Feature is not yet implemented")
-	paramSearchKeys       = []string{ctxKeySpec, ctxKeySubs, ctxKeyVars, ctxKeyKeep}
+	// workerCount specifies how many workers should be used
+	// to process each query statement concurrently.
+	workerCount = runtime.NumCPU() * 2
+
+	// queryIdentFailed occurs when a permission query asks
+	// for a field, meaning a document has to be fetched.
+	queryIdentFailed = errors.New("Found ident but no doc available")
+
+	// errQueryNotExecuted occurs when a transaction has
+	// failed, and the following queries are not executed.
+	errQueryNotExecuted = errors.New("Query not executed")
+
+	// errRaceCondition occurs when a record which is locked
+	// for editing, is updated from within a subquery.
+	errRaceCondition = errors.New("Failed to update the same document recursively")
+
+	// errRecursiveOverload occurs when too many subqueries
+	// are executed within one other, causing an endless loop.
+	errRecursiveOverload = errors.New("Infinite loop when running recursive subqueries")
+
+	// errFeatureNotImplemented occurs when a feature which
+	// has not yet been implemented, has been used in a query.
+	errFeatureNotImplemented = errors.New("Feature is not yet implemented")
+
+	// paramSearchKeys specifies the order in which context
+	// variables should be checked for any specified value.
+	paramSearchKeys = []string{ctxKeySpec, ctxKeySubs, ctxKeyVars, ctxKeyKeep}
 )