mysql union查询、以及分页查询

mysql union查询
一、UNION 操作符用于合并两个或多个 SELECT 语句的结果集。
请注意，UNION 内部的 SELECT 语句必须拥有相同数量的列。列也必须拥有相似的数据类型。同时，每条 SELECT 语句中的列的顺序必须相同。否则会报错。
二、union和 union all的关系和区别：
1.UNION ALL 命令和 UNION 命令几乎是等效的，不过 UNION ALL 命令会列出所有的值。
2.即 ：union会对合并的两个或多个查询的结果集 进行 去重合并的操作。
union all则不会去重，只做合并，因此查出的结果集中 会有重复的记录。

• 查询语句

        SELECT
        *
        FROM evaluate_t_dept_period_base b
        left join pmi_t_department d on (d.id = b.dept_id)
        left join evt_t_accept_flow lf on (lf.last_flow_id = b.flow_id)
        LEFT JOIN evt_t_roll_back_accept_flow df ON (df.accept_flow_id=lf.id)
        WHERE  b.eva_s_time = '2020-07-01 00:00:00' AND b.eva_e_time = '2020-07-31 23:59:59'
        and  d.dept_code LIKE CONCAT((SELECT dept_code FROM pmi_t_department WHERE id = 1),'%')
        and d.dept_type = 1 
        AND '2020-07-31 23:59:59'> DATE_ADD(b.overtime_point,INTERVAL 10 DAY)
        AND b.dept_e_time IS NULL
        UNION 
        SELECT
        *
        FROM evaluate_t_dept_period_base b
        left join pmi_t_department d on (d.id = b.dept_id)
        left join evt_t_accept_flow lf on (lf.last_flow_id = b.flow_id)
        LEFT JOIN evt_t_roll_back_accept_flow df ON (df.accept_flow_id=lf.id)
        WHERE  b.eva_s_time = '2020-07-01 00:00:00' AND b.eva_e_time = '2020-07-31 23:59:59'
        and  d.dept_code LIKE CONCAT((SELECT dept_code FROM pmi_t_department WHERE id = 1),'%')
        and d.dept_type = 1 
        AND '2020-07-31 23:59:59'> DATE_ADD(b.overtime_point,INTERVAL 10 DAY)
        AND b.dept_e_time IS NULL
  

• 分页查询sql

         (
         SELECT
        *
        FROM evaluate_t_dept_period_base b
        left join pmi_t_department d on (d.id = b.dept_id)
        left join evt_t_accept_flow lf on (lf.last_flow_id = b.flow_id)
        LEFT JOIN evt_t_roll_back_accept_flow df ON (df.accept_flow_id=lf.id)
        WHERE  b.eva_s_time = '2020-07-01 00:00:00' AND b.eva_e_time = '2020-07-31 23:59:59'
        and  d.dept_code LIKE CONCAT((SELECT dept_code FROM pmi_t_department WHERE id = 1),'%')
        and d.dept_type = 1 
        AND '2020-07-31 23:59:59'> DATE_ADD(b.overtime_point,INTERVAL 10 DAY)
        AND b.dept_e_time IS NULL
        )
        UNION 
        (
        SELECT
        *
        FROM evaluate_t_dept_period_base b
        left join pmi_t_department d on (d.id = b.dept_id)
        left join evt_t_accept_flow lf on (lf.last_flow_id = b.flow_id)
        LEFT JOIN evt_t_roll_back_accept_flow df ON (df.accept_flow_id=lf.id)
        WHERE  b.eva_s_time = '2020-07-01 00:00:00' AND b.eva_e_time = '2020-07-31 23:59:59'
        and  d.dept_code LIKE CONCAT((SELECT dept_code FROM pmi_t_department WHERE id = 1),'%')
        and d.dept_type = 1 
        AND '2020-07-31 23:59:59'> DATE_ADD(b.overtime_point,INTERVAL 10 DAY)
        AND b.dept_e_time IS NULL
        ) LIMIT 10
  

• count统计sql

     select 
       COUNT(*)
      FROM
       ( 
        (
         SELECT DISTINCT
         b.id
        FROM evaluate_t_dept_period_base b
        left join pmi_t_department d on (d.id = b.dept_id)
        left join evt_t_accept_flow lf on (lf.last_flow_id = b.flow_id)
        LEFT JOIN evt_t_roll_back_accept_flow df ON (df.accept_flow_id=lf.id)
        WHERE  b.eva_s_time = '2020-07-01 00:00:00' AND b.eva_e_time = '2020-07-31 23:59:59'
        and  d.dept_code LIKE CONCAT((SELECT dept_code FROM pmi_t_department WHERE id = 1),'%')
        and d.dept_type = 1 
        AND '2020-07-31 23:59:59'> DATE_ADD(b.overtime_point,INTERVAL 10 DAY)
        AND b.dept_e_time IS NULL
        )
        UNION 
        (
        SELECT DISTINCT
        b.id 
        FROM evaluate_t_dept_period_base b
        left join pmi_t_department d on (d.id = b.dept_id)
        left join evt_t_accept_flow lf on (lf.last_flow_id = b.flow_id)
        LEFT JOIN evt_t_roll_back_accept_flow df ON (df.accept_flow_id=lf.id)
        WHERE  b.eva_s_time = '2020-07-01 00:00:00' AND b.eva_e_time = '2020-07-31 23:59:59'
        and  d.dept_code LIKE CONCAT((SELECT dept_code FROM pmi_t_department WHERE id = 1),'%')
        and d.dept_type = 1 
        AND '2020-07-31 23:59:59'> DATE_ADD(b.overtime_point,INTERVAL 10 DAY)
        AND b.dept_e_time IS NULL
        ) 
       ) AS tmp