Question

使用SQLite处理移动项目时，我遇到了类似于以下代码的查询：

SELECT col_aa, col_ab FROM tbl_a
WHERE col_ac IN (SELECT col_ba FROM tbl_b WHERE col_bb IN (SELECT col_ca FROM tbl_c WHERE col_cb = 1))
AND col_ad IN (SELECT col_ba FROM tbl_b WHERE col_bb IN (SELECT col_ca FROM tbl_c WHERE col_cb = 1))

很明显，这些子查询是多余的和浪费的。

经过一些研究，似乎CTE，公用表表达式可能是一个解决方案，但SQLite上没有该功能。（因此，我不确定WITH temp AS语句是否有效）

有没有更好的方法来重构查询以重用子查询的结果？

Answer 1

假设tbl_b.col_ba是主键（或只是唯一字段），简单JOIN应该有帮助。试试这个SQL：

SELECT 
  col_aa, 
  col_ab 
FROM 
  tbl_a JOIN
    (
      SELECT col_ba 
      FROM tbl_b 
      WHERE col_bb IN 
       (
         SELECT col_ca 
         FROM tbl_c 
         WHERE col_cb = 1
       )
    ) T2 ON (col_ac = T2.col_ba AND col_ad = T2.col_ba)

希望它会有所帮助

Answer 2

您可以创建一个视图，如下所示。...（对不起，代码未经测试）

CREATE VIEW my_view AS 
SELECT col_ba FROM tbl_b WHERE col_bb IN (SELECT col_ca FROM tbl_c WHERE col_cb = 1)

SELECT col_aa, col_ab FROM tbl_a
WHERE col_ac IN (SELECT col_ba FROM my_view)
AND col_ad IN (SELECT col_ba FROM my_view)

如何在sqlite中重用子查询的结果

2 个答案: