Question

有没有办法在values子查询中指定列的数据类型？像(values (...)) as tmp_name (colname::type)？

这样的东西

Contrived Example

假设我有一个包含uuid列的表格：

/* setup */
create table foo (id uuid);
insert into foo values 
    ('aaaabbbbccccddddeeeeffff00001111'),
    ('aaaabbbbccccddddeeeeffff00002222'),
    ('aaaabbbbccccddddeeeeffff00003333');

如果我尝试join使用values子查询对其进行反对，postgres会假定该列为text类型并抛出类型错误（即使相同的字符串有效）直接插入uuid列）：

select foo.id from foo 
inner join (values 
    ('aaaabbbbccccddddeeeeffff00001111'),
    ('aaaabbbbccccddddeeeeffff00000000'))
as tmp (id) on foo.id = tmp.id;

ERROR:  operator does not exist: uuid = text
LINE 5:     as tmp (id) on foo.id = tmp.id;
                                  ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.

明确投出每个值：

如果我将显式强制转换添加到值本身，它会起作用，但是不必抛出每个值并且只是指定列的数据类型是很好的：

select foo.id from foo 
inner join (values
    ('aaaabbbbccccddddeeeeffff00001111'::uuid),
    ('aaaabbbbccccddddeeeeffff00000000'::uuid))
as tmp (id) on foo.id = tmp.id;

Answer 1

您可以在连接谓词上投射一次：

select foo.id from foo 
inner join (values 
    ('aaaabbbbccccddddeeeeffff00001111'),
    ('aaaabbbbccccddddeeeeffff00000000'))
as tmp (id) on foo.id = tmp.id::uuid;

Postgresql：指定values子查询中列的数据类型

Contrived Example

1 个答案: