如何在SQLAlchemy中为Oracle更新查询移动CTE

Question

I am facing the oracle error ORA-00928: missing SELECT keyword with a query, generated by sqlalchemy. The issue was already described and answered here .

My query looks like:

WITH table2 (id) AS (
    SELECT id
    FROM table3
)

UPDATE table SET id=1 
WHERE EXISTS (
    SELECT * 
    FROM table 
    WHERE id IN (SELECT id FROM table2)
)

and gets generated by this:

table2 = session.query(table3.id).cte()
update(table).where(exists().where(table.id.in_(table2))).values(id=1)

Now I am wondering how to tell sqlachemy to put the CTEs inside the WHERE clause and not above the UPDATE .

UPDATE table SET id=1 
WHERE EXISTS (
    WITH table2 (id) AS (
        SELECT id
        FROM table3
    )

    SELECT * 
    FROM table 
    WHERE id IN (SELECT id FROM table2)
)

Answer 1

CTE is a nice way to extract an inline view from the query and, by doing so, make your code easier to read and maintain.

When the CTE wasn't invented yet, we used inline views. Here are a few examples (based on Scott's schema) to show what I mean.

First, a CTE:

SQL> with tab as
  2    (select deptno from dept
  3     where deptno > 10
  4    )
  5  select e.deptno, count(*)
  6  from emp e join tab t on t.deptno = e.deptno
  7  group by e.deptno;

    DEPTNO   COUNT(*)
---------- ----------
        30          6
        20          5

It can be moved into an inline view:

SQL> select e.deptno, count(*)
  2  from emp e join (select deptno from dept
  3                   where deptno > 10
  4                  ) t on t.deptno = e.deptno
  5  group by e.deptno;

    DEPTNO   COUNT(*)
---------- ----------
        30          6
        20          5

Or, using the old syntax, where tables (in the FROM clause) were separated by commas and joins were done within the WHERE clause (this might look familiar):

SQL> select e.deptno, count(*)
  2  from emp e,
  3      (select deptno from dept
  4       where deptno > 10
  5      ) t
  6  where t.deptno = e.deptno
  7  group by e.deptno;

    DEPTNO   COUNT(*)
---------- ----------
        30          6
        20          5

---

It means that your query might look like this; note the comment which shows position of your CTE:

update table set
  id = 1
  where exists (select *
                from table
                where id in (select id 
                             from 
                               (select id from table3)  --> this line is your CTE
                            )
               );