谁能解释postgresql中的 :: 含义？ [复制]

Question

我有以下查询可以正常工作，但不知道 :: 在 postgresql 中的含义和用法。

select (
    select ( 
        case when 1 > 0 then 1::float / (
            select count(id) from transactions_products where transaction_id in (
            select id from transactions_transactions tt 
            where status = 3 and fi = 355 
                and (invoice_date >= 1420754400) 
                and (invoice_date <= 1421099999) 
                and (tt.division_id = 107) 
                and (tt.department_id = 210) 
        ) and is_vehicle = 1 
    )::float else 0 end)
 limit 1) as f_4

Answer 1

:: 是 PostgreSQL 的 cast 运算符。

Answer 2

简短、轻松的回答：它将值转换为浮点数。