Question

我尝试创建一个查询，其中结果可以来自两个不同的表，具体取决于第一个表的大小。甚至可能有类似的东西吗？

SELECT 
    CASE WHEN COUNT(table1.column1) > 5
    THEN
        column1,
        column2,
        column3
        FROM table1
    ELSE
        column1,
        column2,
        column3
        FROM table2
    END

使用此代码，我得到了类似的结果：

ERROR:  syntax error at or near ","
LINE 4:   column1,

Answer 1

with c (c) as (select count(c1) from t)
select c1, c2, c3
from t
where (select c from c) > 5
union all
select c1, c2, c3
from r
where (select c from c) <= 5

相应的列必须属于同一类型。或者换成相同的类型。

WITH clause

UNION clause

在PostgreSQL中使用CASE来选择不同的FROM

1 个答案: