将oracle db上的3 x sql查询合并为1。

SELECT *
FROM (
    SELECT column1, column2
    FROM table1
    WHERE condition1
) subquery1
JOIN (
    SELECT column3, column4
    FROM table2
    WHERE condition2
) subquery2 ON subquery1.column1 = subquery2.column3
JOIN (
    SELECT column5, column6
    FROM table3
    WHERE condition3
) subquery3 ON subquery2.column4 = subquery3.column5;

SELECT column1, column2
FROM table1
WHERE condition1
UNION
SELECT column3, column4
FROM table2
WHERE condition2
UNION
SELECT column5, column6
FROM table3
WHERE condition3;

WITH subquery1 AS (
    SELECT column1, column2
    FROM table1
    WHERE condition1
), subquery2 AS (
    SELECT column3, column4
    FROM table2
    WHERE condition2
), subquery3 AS (
    SELECT column5, column6
    FROM table3
    WHERE condition3
)
SELECT *
FROM subquery1
JOIN subquery2 ON subquery1.column1 = subquery2.column3
JOIN subquery3 ON subquery2.column4 = subquery3.column5;