Question

在PostgreSQL中，如何将SELECT语句返回的数据集中的BIT值替换为STRING（字，无数字）？一般而言，我对SQL还是很陌生，所以我的经验和Google搜索并没有被证明过。

在这种情况下，c.visible是一个存储0（可见）或1（不可见）的位值。在我的查询中，我想显示c.visible = 0的所有结果，但显示“该课程对学生可见”。而不是此select语句返回的数据集中的“ 0”。我尝试将其强制转换为SELECT语句中的文本，然后更改WHERE子句中CASE WHEN语句中的值，但这会导致无效的输入语法错误。 c.visibility是数据库中记录此信息的唯一属性。

例如：

--------------------------------------------------------
| CourseName | ID | CourseVisibility                   |
--------------------------------------------------------
|    ABC     | 10 | This course is visible to students.|
--------------------------------------------------------
|    DEF     | 22 | This course is visible to students.|
--------------------------------------------------------

SELECT c.fullname AS CourseName, c.id AS ID, CAST(c.visible AS TEXT) AS CourseVisibilty
FROM prefix_course c, prefix_logstore_standard_log lsl
WHERE
    c.visible = 0 
    CASE WHEN c.visible = '0' 
        THEN c.visible = 'This course is visible to students.'
    END
    AND lsl.courseid = c.id
    AND lsl.timecreated BETWEEN extract(epoch from NOW()- INTERVAL '12 month') AND extract(epoch from NOW())
GROUP BY c.fullname, c.id, c.visible

ERROR:  invalid input syntax for integer: "This course is visible to students."
LINE 5:   THEN c.visible = 'This course is visible to students.' 
                           ^

执行此操作的正确方法是什么？

Answer 1

您不能在where子句中修改返回的值，但是可以在select子句中进行修改

SELECT 
    c.fullname AS CourseName,
    c.id AS ID,
    CASE WHEN c.visible = '0' 
    THEN 'This course is visible to students.'
    ELSE 'This course is not visible to students.'
    END AS CourseVisibilty
FROM prefix_course c, prefix_logstore_standard_log lsl
WHERE
    lsl.courseid = c.id
    AND lsl.timecreated BETWEEN extract(epoch from NOW()- INTERVAL '12 month') AND extract(epoch from NOW())
GROUP BY c.fullname, c.id, c.visible

如何在PostgreSQL的select语句中用STRING值替换BIT

1 个答案: