Question

我正在尝试选择具有特定列名称的行，并按其他列名称排序。

这是我的问题，进入N个简化表：

table 1: id, username, datetime, comment

table 2: id, username, datetime, vote

table N: id, username, datetime, bought

我希望能够在所有N个表中选择按日期时间排序的username='Some Name'的所有行。

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顺便说一下，有没有人知道学习和练习高级SQL的好书或资源？（尝试过SQLZoo，但是他们没有足够的先进例子......然后还有太高级的例子，我仍然难以接受）

Answer 1

如果您希望同时对所有表格进行排序（表3中的较新记录显示在表2中的某些表格之前），

跨多个表执行此操作的最简单方法是使用UNION：

(SELECT id, username, datetime FROM table 1 WHERE username = 'Some Name')
UNION 
(SELECT id, username, datetime FROM table 2 WHERE username = 'Some Name')
UNION
(SELECT id, somethingelse AS username, date as datetime FROM table 3 WHERE somethingelse = 'Some Name')
....
ORDER BY datetime DESC

请注意，当您使用这样的联合时，所有的select语句都应该返回相同数量的列并且命名相同（您可以使用别名，如我在上面的表3中所示）

Answer 2

在查询中对表进行别名，即

SELECT t1.id, t2.username, ... FROM table1 as t1

Answer 3

您可以从不同的表中选择相同的列名称，如：

SELECT table1.username as t1user, table2.username as t2user...

Answer 4

您可以使用UNIONS

选择必须是这样的：

(SELECT comment, date FROM table1 WHERE username='Some Name')
UNION
(SELECT vote, date FROM table2 WHERE username='Some Name')
...
UNION
(SELECT bought, date FROM tableN WHERE username='Some Name')
ORDER BY date LIMIT 100;

Answer 5

 display_error($this->entity);
        $result = get_leave_status($this->entity);

        start_table(TABLESTYLE, "width=60%");

        $th = array(_("#"),
           _("Login Date"),
            _("Login Time"),
            _("Reason"),
            _("Status"),
            _(" "),

        );

        table_header($th);
           $sl=1;
            while($sl<13){

        display_error($sl);
        $str = ($sl < 10) ? 0 . $sl : $sl;
        $sql="SELECT login_time,login_date,early_leave_reason FROM ".TB_PREF."hcm_attendance_".$str." WHERE emp_code=".  db_escape($this->entity);

        $sl++;
    $result = db_query($sql, "Can't make query in loan_req table.");



        $k = 0;
        $i = 1;
        while ($myrow = db_fetch($result)) {
            alt_table_row_color($k);

            label_cell($i,'align=center');
            label_cell(sql2date($myrow["login_date"]),'align=center');
            label_cell($myrow["login_time"],'align=center');



            label_cell($myrow["early_leave_reason"], "Width=30%");

            if ($myrow["status"] == 1)
                label_cell('Approved');
            elseif ($myrow["status"] == 2)
                label_cell('Rejected');
            else {
                label_cell(viewer_link('Pending',"payroll/inquiry/leave_document.php?eno=".$this->vendor_no.'&lid='.$myrow['id']));

                edit_button_cell("{$this->name}Edit[{$myrow['id']}]", _("EDIT"));
            }
            end_row();
            $i++;
        }

            }
        end_table(1);

here i have used $sl to increment table name like 0_hcm_attendance_01,0_hcm_attendance_02 -------to 0_hcm_attendance_12

here TB_PREF=0;

TB_PREF."hcm_attendance_".$str

MySQL Select，多个表中具有相同名称的列，由具有相同名称的另一列排序

5 个答案: