错误号：1242 子查询返回超过 1 行

Question

我有一个名为 view_att_tabulation 的表，它保存员工在给定日期的每日出勤信息，而 tbl_employ 保存有关员工的所有信息。我想检索给定日期所有活跃 = Y、状态为 1、employee_id 以“W”开头的员工的出勤情况。下面的代码对于今天和昨天总是可以正常工作，但对于之前的日期总是会抛出错误。对我哪里出错有什么建议吗？

SELECT emp_id, employ_id, employ_label, employ_name, employ_shortname, status, active_flag,
    (SELECT
        CASE
        WHEN (
            SELECT view_att_tabulation.emp_id FROM view_att_tabulation 
            WHERE view_att_tabulation.emp_id = tbl_employ.emp_id AND 
            employ_workdate = '2024-01-17' AND attendance_type LIKE 'PRESENT'
        )
        THEN 'PRESENT'
        WHEN
        (
            SELECT view_att_tabulation.emp_id FROM view_att_tabulation 
            WHERE view_att_tabulation.emp_id = tbl_employ.emp_id AND 
            employ_workdate ='2024-01-17' AND attendance_type LIKE 'ABSENT'
        )
        THEN 'ABSENT'
        ELSE ''
    END
   )AS employ_att
FROM tbl_employ
WHERE  active_flag = 'Y' AND status = '1' AND employ_id LIKE 'W%'
ORDER BY employ_att, `tbl_employ`.`employ_id` ASC;

Answer 1

SELECT 
    tbl_employ.emp_id,
    tbl_employ.employ_id,
    tbl_employ.employ_label,
    tbl_employ.employ_name,
    tbl_employ.employ_shortname,
    tbl_employ.status,
    tbl_employ.active_flag,
    CASE
        WHEN view_att_tabulation.attendance_type = 'PRESENT' THEN 'PRESENT'
        WHEN view_att_tabulation.attendance_type = 'ABSENT' THEN 'ABSENT'
        ELSE ''
    END AS employ_att
FROM 
    tbl_employ
LEFT JOIN 
    view_att_tabulation ON tbl_employ.emp_id = view_att_tabulation.emp_id
        AND view_att_tabulation.employ_workdate = '2024-01-17'
WHERE  
    tbl_employ.active_flag = 'Y' 
    AND tbl_employ.status = '1' 
    AND tbl_employ.employ_id LIKE 'W%'
ORDER BY 
    employ_att, tbl_employ.employ_id ASC;

基于

LEFT JOIN

和

view_att_tabulation

，将子查询替换为

emp_id

上的

employ_workdate

。然后，我直接在主查询中使用

CASE

语句来根据

employ_att

确定

attendance_type

值。

这应该会简化您的查询，并可能有助于解决您在今天或昨天之前的日期所面临的问题。确保根据您的需要调整

WHERE

子句和

view_att_tabulation.employ_workdate

比较中的日期条件。