Question

在以下查询中，1/2的答案始终为零，而应为0.5。你能告诉我如何将两个int列转换成float / double吗？

SELECT 1/2, total, sb_ondate, likes
  FROM (
      SELECT sb_ondate, COUNT(*) AS total,
             STRFTIME("%w",sb_ondate) AS weekDay,
             COUNT(CASE WHEN sb_reaction = 'like' THEN sb_id END) AS likes
        FROM diet
    GROUP BY weekDay) AS f;

感谢。

Answer 1

Cast两个除数中的一个为real：

SELECT 1 / CAST(2 AS REAL),...

示例交互式Python会话：

>>> import sqlite3
>>> c = sqlite3.connect(':memory:')
>>> c.execute("create table t (a int,b int);")
<sqlite3.Cursor object at 0x7f9b0e9539d0>
>>> c.execute("insert into t values (1,2)")
<sqlite3.Cursor object at 0x7f9b0e953ad8>
>>> conn.execute("select a / cast(b as real) from t").fetchone()
(0.5,)

Answer 2

将.0添加到其中一个常量：

sqlite> select 1/2;
1/2
----------
0
sqlite> select 1.0/2;
1.0/2
----------
0.5

类型铸造问题

2 个答案: