[＋表]と[－表]を統合して時系列で二列に並べて累積を逐一計算する場合は、
以下のような感じ
┌──────────────────────────────────────┐
│SELECT [±表].[日付],                                                       │
│       CASE [±表].[±区分]                                                 │
│         WHEN 1 THEN '＋'                                                   │
│         WHEN 2 THEN '－'                                                   │
│       END AS [区分],                                                       │
│       [±表].[＋値],                                                       │
│       [±表].[－値],                                                       │
│       ISNULL((                                                             │
│           SELECT SUM([＋表].[値])                                          │
│               FROM [＋表]                                                  │
│               WHERE [＋表].[日付] < [±表].[日付]                          │
│                  OR  ([＋表].[日付]   =  [±表].[日付]                     │
│                   AND [＋表].[±区分] <= [±表].[±区分])                  │
│       ), 0) - ISNULL((                                                     │
│           SELECT SUM([－表].[値])                                          │
│               FROM [－表]                                                  │
│               WHERE [－表].[日付] < [±表].[日付]                          │
│                  OR  ([－表].[日付]   =  [±表].[日付]                     │
│                   AND [－表].[±区分] <= [±表].[±区分])                  │
│       ), 0) AS [累積]                                                      │
│    FROM (                                                                  │
│        SELECT [日付],                                                      │
│               1         AS [±区分],                                       │
│               SUM([値]) AS [＋値],                                         │
│               NULL      AS [－値]                                          │
│            FROM [＋表]                                                     │
│            GROUP BY [日付]                                                 │
│        UNION ALL                                                           │
│        SELECT [日付],                                                      │
│               2         AS [±区分],                                       │
│               NULL      AS [＋値],                                         │
│               SUM([値]) AS [－値]                                          │
│            FROM [－表]                                                     │
│            GROUP BY [日付]                                                 │
│    ) AS [±表]                                                             │
│    ORDER BY [±表].[日付]   ASC,                                           │
│             [±表].[±区分] ASC;                                           │
└──────────────────────────────────────┘
[－表]がなければ、もっとシンプルになる。
┌──────────────────────────────────────┐
│SELECT [±表].[日付],                                                       │
│       [±表].[＋値],                                                       │
│       ISNULL((                                                             │
│           SELECT SUM([＋表].[値])                                          │
│               FROM [＋表]                                                  │
│               WHERE [＋表].[日付] <= [±表].[日付]                         │
│       ), 0) AS [累積]                                                      │
│    FROM (                                                                  │
│        SELECT [日付],                                                      │
│               SUM([値]) AS [＋値]                                          │
│            FROM [＋表]                                                     │
│            GROUP BY [日付]                                                 │
│    ) AS [±表]                                                             │
│    ORDER BY [±表].[日付] ASC;                                             │
└──────────────────────────────────────┘