SQL DML 數據操縱語句

前言

• DML（Data Manipulation Language）語句：數據操縱語句，用於添加、刪除、更新和查詢數據庫記錄，並檢查數據完整性。經常使用的語句關鍵字主要包括 insert、delete、update 和 select 等。

• 經常使用約束類型

  約束類型	解釋
  not null	非空約束，設定的內容在添加數據的時候不能是 null 的
  unique	惟一約束，值是惟一的
  primary key	主鍵約束，非空惟一
  auto_increment	主鍵自增約束，主鍵爲數值型
  foreign key	外鍵約束，B 表使用 A 表的主鍵

• 經常使用 where 查詢條件

  where 條件	解釋
  > < <= >= <>	大於、小於、大於（小於）等於、不等於
  between...and...	在某一區間，閉區間，效果同 and
  in(set)	在 in 列表中的值，如 in(100, 200)，效果同 or
  like 通配符	模糊查詢：% 匹配多個字符，如 first_name like "a%"；_ 匹配一個字符，如 first_name like "a_"。
  is null	爲空
  is not null	不爲空
  and	同時成立
  or	任一成立
  not	不成立，如 where not(salary > 100);

• 經常使用聚合查詢條件

  統計函數	解釋
  count()	求總數
  avg()	求平均數
  sum()	求和
  max()	求最大值
  min()	求最小值

一、DML 插入記錄語句

• 含可空字段、非空可是含有默認值的字段、自增字段，能夠不用在 insert 後的字段列表裏面出現，values 後面只寫對應字段名稱的 value，這些沒有寫的字段能夠自動設置爲 NULL、默認值、自增的下一個數字。

• 1）插入單條記錄

  # 插入單條記錄，插入到指定列
  # insert into 
      表名 
      (列名1, 列名2, ...) 
    values 
      (值1, 值2, ...);
  > insert into student (name, age, class) values ("xiao bai", 18, "one");
  
      Query OK, 1 row affected (0.09 sec)

  # 插入單條記錄，插入到全部列
  # insert into 
      表名 
    values 
      (值1, 值2, ...);
  > insert into student values (2, "li si", 20, 90, "two", "aaaaaaaa");
  
      Query OK, 1 row affected (0.04 sec)

• 2）插入多條記錄

  # 插入多條記錄，插入到指定列
  # insert into 
      表名 
      (列名1, 列名2, ...) 
    values 
      (值1, 值2, ...), 
      (值1, 值2, ...), 
      ...;
  > insert into student (name, age, class) values ("zhang san", 18, "one"), ("li si", 19, "one");
  
      Query OK, 2 rows affected (0.03 sec)
      Records: 2  Duplicates: 0  Warnings: 0

  # 插入多條記錄，插入到全部列
  # insert into 
      表名 
    values 
      (值1, 值2, ...), 
      (值1, 值2, ...), 
      ...;
  > insert into student values (5, "zhang san", 20, 90, "two", "aaaaaaaa"), (6, "li si", 21, 92, "two", "bbbbbbbb");
  
      Query OK, 2 rows affected (0.08 sec)
      Records: 2  Duplicates: 0  Warnings: 0

二、DML 刪除記錄語句

• delete 一條一條刪除，不清空 auto_increment 記錄數，truncate 直接將表刪除重建表，清空 auto_increment 記錄數。

• 不論時單表仍是多表，不加 where 條件將會把表的全部記錄刪除。

• 1）刪除單個表中的記錄

  # 刪除單個表中的記錄，刪除全部表記錄
  # delete from 表名;
  > delete from student;
  
      Query OK, 5 rows affected (0.08 sec)

  # 刪除單個表中的記錄，刪除知足條件的表記錄
  # delete from 表名 where 條件;
  > delete from student where no = 5;
  
      Query OK, 1 row affected (0.11 sec)

  # 刪除單個表中的記錄，刪除全部表記錄
  # truncate table 表名;
  > truncate table student;
  
      Query OK, 0 rows affected (0.08 sec)

• 2）刪除多個表中的記錄

  # 刪除多個表中的記錄，若是 from 後面的表用別名，delete 後面也要用相應的別名
  # delete 
      表名1, 
      表名2, 
      ... 
    from 
      表名1, 
      表名2, 
      ...
    [where 條件];
  > delete
      a, b
    from
      emp a, dept b
    where
      a.dept.no = b.deptno and a.deptno = 3;
  
      Query OK, 2 rows affected (0.04 sec)

三、DML 更新記錄語句

• 1）更新單個表中的記錄

  # 更新單個表中的記錄，全部指定列記錄
  # update 表名 set 字段名 = 值, 字段名 = 值;
  > update student set age = 18;
  
      Query OK, 4 rows affected (0.02 sec)
      Rows matched: 6  Changed: 4  Warnings: 0

  # 更新單個表中的記錄，知足條件的指定列記錄
  # update 表名 set 字段名 = 值, 字段名 = 值 where 條件;
  > update student set age = 19 where class = "two";
  
      Query OK, 3 rows affected (0.02 sec)
      Rows matched: 3  Changed: 3  Warnings: 0

• 2）更新多個表中的記錄

  # 更新多個表中的記錄
  # update 
      表名1, 
      表名2, 
      ... 
    set 
      表名1.字段名1 = 值, 
      表名1.字段名2 = 值,
      表名2.字段名1 = 值,
      表名2.字段名2 = 值,
      ...
    [where 條件];
  > update 
      emp a, dept b
    set 
      a.sal = a.sal * b.deptno,
      b.deptname = a.ename
    where
      a.deptno = b.deptno;
  
      Query OK, 3 rows affected (0.04 sec)
      Rows matched: 5  Changed: 3  Warnings: 0

  • 多表的更新語法更多的用在根據一個表的字段來動態的更新另一個表的字段。

四、DML 查詢記錄語句

4.1 查詢單表記錄

• 1）簡單查詢

  # 查詢單表記錄，查詢全部數據
  # select * from 表名;
  > select * from zhangwu;
  
      +----+-----------------+-------+
      | id | name            | money |
      +----+-----------------+-------+
      |  1 | chifanzhichu    |   247 |
      |  2 | gongzishouru    | 12345 |
      |  3 | fuzhuangzhichu  |  1000 |
      |  4 | chifanzhichu    |   325 |
      |  5 | gupiaoshouru    |  8000 |
      |  6 | damajiangzhichu |  8000 |
      |  7 | NULL            |  5000 |
      +----+-----------------+-------+
      7 rows in set (0.00 sec)

  # 查詢單表記錄，查詢指定字段記錄
  # select 字段1, 字段2, ... from 表名;
  > select id, name from zhangwu;
  
      +----+-----------------+
      | id | name            |
      +----+-----------------+
      |  1 | chifanzhichu    |
      |  2 | gongzishouru    |
      |  3 | fuzhuangzhichu  |
      |  4 | chifanzhichu    |
      |  5 | gupiaoshouru    |
      |  6 | damajiangzhichu |
      |  7 | NULL            |
      +----+-----------------+
      7 rows in set (0.00 sec)

• 2）去重查詢

  # 查詢單表記錄，去除重複記錄
  # select distinct 字段名 from 表名;
  > select distinct money from zhangwu;
  
      +-------+
      | money |
      +-------+
      |   247 |
      | 12345 |
      |  1000 |
      |   325 |
      |  8000 |
      |  5000 |
      +-------+
      6 rows in set (0.00 sec)

• 3）條件查詢

  # 查詢單表記錄，查詢全部知足條件的記錄
  # select * from 表名 where 條件;
  > select * from zhangwu where money >= 8000;
  
      +----+-----------------+-------+
      | id | name            | money |
      +----+-----------------+-------+
      |  2 | gongzishouru    | 12345 |
      |  5 | gupiaoshouru    |  8000 |
      |  6 | damajiangzhichu |  8000 |
      +----+-----------------+-------+
      3 rows in set (0.00 sec)

• 4）別名查詢

  • 使用 as 關鍵字標示別名，可省略。

  # 查詢單表記錄，表別名查詢
  # select 字段名 from 表名 [as] 別名;
  > select name from zhangwu as zw;
  
      +-----------------+
      | name            |
      +-----------------+
      | chifanzhichu    |
      | gongzishouru    |
      | fuzhuangzhichu  |
      | chifanzhichu    |
      | gupiaoshouru    |
      | damajiangzhichu |
      | NULL            |
      +-----------------+
      7 rows in set (0.00 sec)

  # 查詢單表記錄，列別名查詢
  # select 字段名 [as] 別名 from 表名;
  > select name as na from zhangwu;
  
      +-----------------+
      | na              |
      +-----------------+
      | chifanzhichu    |
      | gongzishouru    |
      | fuzhuangzhichu  |
      | chifanzhichu    |
      | gupiaoshouru    |
      | damajiangzhichu |
      | NULL            |
      +-----------------+
      7 rows in set (0.00 sec)

• 5）列運算查詢

  • 能夠直接對列查詢的結果進行運算。

  # 查詢單表記錄，列運算查詢
  # select 字段名(列運算) from 表名;
  > select money + 10000 from zhangwu;
  
      +---------------+
      | money + 10000 |
      +---------------+
      |         10247 |
      |         22345 |
      |         11000 |
      |         10325 |
      |         18000 |
      |         18000 |
      |         15000 |
      +---------------+
      7 rows in set (0.00 sec)

• 6）排序查詢

  • 排序方式：asc 升序（默認，可省略），desc 降序，排序需放在 where 條件以後。

  # 查詢單表記錄，單列排序查詢
  # select 字段名 from 表名 [where 條件] order by 列名 排序方式;
  > select 
      *
    from 
      zhangwu 
    where 
      money > 1000 
    order by 
      money asc;
  
      +----+-----------------+-------+
      | id | name            | money |
      +----+-----------------+-------+
      |  7 | NULL            |  5000 |
      |  5 | gupiaoshouru    |  8000 |
      |  6 | damajiangzhichu |  8000 |
      |  2 | gongzishouru    | 12345 |
      +----+-----------------+-------+
      4 rows in set (0.00 sec)

  # 查詢單表記錄，多列排序查詢
  # select 字段名 from 表名 [where 條件] order by 列名 排序方式, 列名 排序方式, ...;
  > select 
      *
    from 
      zhangwu 
    where 
      money > 1000 
    order by 
      money asc, id desc;
  
      +----+-----------------+-------+
      | id | name            | money |
      +----+-----------------+-------+
      |  7 | NULL            |  5000 |
      |  6 | damajiangzhichu |  8000 |
      |  5 | gupiaoshouru    |  8000 |
      |  2 | gongzishouru    | 12345 |
      +----+-----------------+-------+
      4 rows in set (0.00 sec)

• 7）限制查詢

  • limit：只獲取查詢結果中從起始偏移量開始的指定行數的記錄。
  • limit 屬於 MySQL 擴展後的語法，在其它數據庫上並不能通用。

  # 查詢單表記錄，限制查詢
  # select 字段名 from 表名 [where 條件] [order by 列名 排序方式] limit [起始偏移量] 獲取的行數
  > select 
      *
    from 
      zhangwu 
    where 
      money > 1000 
    order by 
      money asc, id desc
    limit
      3;
  
      +----+-----------------+-------+
      | id | name            | money |
      +----+-----------------+-------+
      |  7 | NULL            |  5000 |
      |  6 | damajiangzhichu |  8000 |
      |  5 | gupiaoshouru    |  8000 |
      +----+-----------------+-------+
      3 rows in set (0.01 sec)

• 8）聚合查詢

  # 查詢單表記錄，求總數、統計
  # select count(字段名) from 表名;
  > select count(id) from zhangwu;
  
      +-----------+
      | count(id) |
      +-----------+
      |         7 |
      +-----------+
      1 row in set (0.00 sec)

  # 查詢單表記錄，求和
  # select sum(字段名) from 表名;
  > select sum(money) from zhangwu;
  
      +------------+
      | sum(money) |
      +------------+
      |      34917 |
      +------------+
      1 row in set (0.00 sec)

  # 查詢單表記錄，求平均數
  # select avg(字段名) from 表名;
  > select avg(money) from zhangwu;
  
      +-------------------+
      | avg(money)        |
      +-------------------+
      | 4988.142857142857 |
      +-------------------+
      1 row in set (0.00 sec)

  # 查詢單表記錄，求最大值
  # select max(字段名) from 表名;
  > select max(money) from zhangwu;
  
      +------------+
      | max(money) |
      +------------+
      |      12345 |
      +------------+
      1 row in set (0.01 sec)

  # 查詢單表記錄，求最小值
  # select min(字段名) from 表名;
  > select min(money) from zhangwu;
  
      +------------+
      | min(money) |
      +------------+
      |        247 |
      +------------+
      1 row in set (0.00 sec)

• 9）分組查詢

  • having 是對分組後的結果進行條件過濾，而 where 是在分組前就對記錄進行過濾。
  • 若是邏輯容許，儘量的使用 where 先過濾記錄，由於這樣結果集減少，將對聚合的效率大大提升，最後再根據邏輯看是否用 having 進行再過濾。

  # 查詢單表記錄，分組查詢
  # select 
      字段名 
    from 
      表名
    [where 條件] 
    group by 
      分組字段名 
    [order by 排序字段名 排序方式];
  > select class, count(no), avg(score) from student group by class;
  
      +-------+-----------+------------+
      | class | count(no) | avg(score) |
      +-------+-----------+------------+
      | one   |         3 |    81.6667 |
      | two   |         2 |    77.5000 |
      | three |         2 |    83.0000 |
      +-------+-----------+------------+
      3 rows in set (0.00 sec)

  # 查詢單表記錄，分組後過濾查詢
  # select 
      字段名 
    from 
      表名
    [where 條件] 
    group by 
      分組字段名 
    having 
      分組後的過濾條件
    [order by 排序字段名 排序方式];
  > select class, count(no), avg(score) from student group by class having avg(score) >= 80;
  
      +-------+-----------+------------+
      | class | count(no) | avg(score) |
      +-------+-----------+------------+
      | one   |         3 |    81.6667 |
      | three |         2 |    83.0000 |
      +-------+-----------+------------+
      2 rows in set (0.00 sec)

  # 查詢單表記錄，分組後彙總查詢，對分類後的結果進行再彙總
  # select 
      字段名 
    from 
      表名
    [where 條件] 
    group by 
      分組字段名 
    with rollup 
    [order by 排序字段名 排序方式];
  > select class, count(no), avg(score) from student group by class with rollup;
  
      +-------+-----------+------------+
      | class | count(no) | avg(score) |
      +-------+-----------+------------+
      | one   |         3 |    81.6667 |
      | three |         2 |    77.5000 |
      | two   |         2 |    83.0000 |
      | NULL  |         7 |   242.1667 |
      +-------+-----------+------------+
      4 rows in set (0.00 sec)

• 10）子查詢

  • 某些狀況下，當進行查詢的時候，須要的條件是另一個 select 語句的結果，這個時候，就要用到子查詢。
  • 用於子查詢的關鍵字主要包括 in、not in、=、!=、exists、not exists、any、all 等。
  • 子查詢，理論上能夠出如今任意位置，在 where 和 from 子句中較多。

  • where 子查詢通常返回單行單列、單行多列、多行單列（in、any、all）的數據，from 子查詢通常返回多行多列的數據。

  • where 子查詢

  # 查詢單表記錄，where 單行單列子查詢
  # select 字段名 from 表名 where 條件(子查詢語句);
  > select 
      *
    from 
      student 
    where 
      score > (select 
                 score 
               from 
                 student 
               where 
                 name = "xiao bai"
               )
    order by score asc;
  
      +----+-----------+------+-------+-------+----------+
      | no | name      | age  | score | class | address  |
      +----+-----------+------+-------+-------+----------+
      |  1 | xiao hei  |   18 |    80 | one   | NULL     |
      |  6 | li si     |   19 |    80 | two   | bbbbbbbb |
      |  3 | zhang san |   18 |    95 | one   | NULL     |
      +----+-----------+------+-------+-------+----------+
      3 rows in set (0.00 sec)

  # 查詢單表記錄，where 單行多列子查詢
  # select 字段名 from 表名 where 條件(子查詢語句);
  > select 
      *
    from 
      student 
    where 
      (age, class) = (select 
                        age, class 
                      from 
                        student 
                      where 
                        name = "zhang san"
                     )
    order by score asc;
  
      +----+-----------+------+-------+-------+---------+
      | no | name      | age  | score | class | address |
      +----+-----------+------+-------+-------+---------+
      |  1 | xiao hei  |   18 |    80 | one   | NULL    |
      |  3 | zhang san |   18 |    95 | one   | NULL    |
      |  4 | wang wu   |   18 |    70 | one   | NULL    |
      +----+-----------+------+-------+-------+---------+
      3 rows in set (0.00 sec)

  • where in 子查詢

  # 查詢單表記錄，where 多行單列 in 子查詢，與普通的 in 條件相似，若是子查詢記錄數惟一，還可使用 = 代替 in
  # select 字段名 from 表名 where 條件(in 子查詢語句);
  > select 
      *
    from 
      student 
    where 
      age in (select 
                age 
              from 
                student 
              where 
                class = "one"
             )
    order by age asc;
  
      +----+-----------+------+-------+-------+----------+
      | no | name      | age  | score | class | address  |
      +----+-----------+------+-------+-------+----------+
      |  4 | wang wu   |   18 |    70 | one   | NULL     |
      |  1 | xiao hei  |   18 |    80 | one   | NULL     |
      |  3 | zhang san |   19 |    95 | one   | NULL     |
      |  6 | li si     |   19 |    80 | two   | bbbbbbbb |
      |  7 | xiao bai  |   19 |    79 | three | NULL     |
      |  2 | da bai    |   19 |    75 | two   | aaaaaaaa |
      +----+-----------+------+-------+-------+----------+
      6 rows in set (0.00 sec)

  • where any 子查詢

  # 查詢單表記錄，where 多行單列 =any 子查詢，與 in 子查詢同樣
  # select 字段名 from 表名 where 條件(=any 子查詢語句);
  > select 
      *
    from 
      student 
    where 
      age = any (select 
                   age 
                 from 
                   student 
                 where 
                   class = "one"
                )
    order by age asc;
  
      +----+-----------+------+-------+-------+----------+
      | no | name      | age  | score | class | address  |
      +----+-----------+------+-------+-------+----------+
      |  4 | wang wu   |   18 |    70 | one   | NULL     |
      |  1 | xiao hei  |   18 |    80 | one   | NULL     |
      |  3 | zhang san |   19 |    95 | one   | NULL     |
      |  6 | li si     |   19 |    80 | two   | bbbbbbbb |
      |  7 | xiao bai  |   19 |    79 | three | NULL     |
      |  2 | da bai    |   19 |    75 | two   | aaaaaaaa |
      +----+-----------+------+-------+-------+----------+
      6 rows in set (0.01 sec)

  # 查詢單表記錄，where 多行單列 >any 子查詢，大於最小值
  # select 字段名 from 表名 where 條件(>any 子查詢語句);
  > select 
      *
    from 
      student 
    where 
      age > any (select 
                   age 
                 from 
                   student 
                 where 
                   class = "one"
                )
    order by age asc;
  
      +----+-----------+------+-------+-------+----------+
      | no | name      | age  | score | class | address  |
      +----+-----------+------+-------+-------+----------+
      |  2 | da bai    |   19 |    75 | two   | aaaaaaaa |
      |  3 | zhang san |   19 |    95 | one   | NULL     |
      |  6 | li si     |   19 |    80 | two   | bbbbbbbb |
      |  7 | xiao bai  |   19 |    79 | three | NULL     |
      |  5 | ma liu    |   20 |    78 | three | NULL     |
      +----+-----------+------+-------+-------+----------+
      5 rows in set (0.00 sec)

  # 查詢單表記錄，where 多行單列 <any 子查詢，小於最大值
  # select 字段名 from 表名 where 條件(<any 子查詢語句);
  > select 
      *
    from 
      student 
    where 
      age < any (select 
                   age 
                 from 
                   student 
                 where 
                   class = "one"
                )
    order by age asc;
  
      +----+----------+------+-------+-------+---------+
      | no | name     | age  | score | class | address |
      +----+----------+------+-------+-------+---------+
      |  1 | xiao hei |   18 |    80 | one   | NULL    |
      |  4 | wang wu  |   18 |    70 | one   | NULL    |
      +----+----------+------+-------+-------+---------+
      2 rows in set (0.00 sec)

  • where all 子查詢

  # 查詢單表記錄，where 多行單列 >all 子查詢，大於最大值
  # select 字段名 from 表名 where 條件(>all 子查詢語句);
  > select 
      *
    from 
      student 
    where 
      age > all (select 
                   age 
                 from 
                   student 
                 where 
                   class = "one"
                )
    order by age asc;
  
      +----+--------+------+-------+-------+---------+
      | no | name   | age  | score | class | address |
      +----+--------+------+-------+-------+---------+
      |  5 | ma liu |   20 |    78 | three | NULL    |
      +----+--------+------+-------+-------+---------+
      1 row in set (0.00 sec)

  # 查詢單表記錄，where 多行單列 <all 子查詢，小於最小值
  # select 字段名 from 表名 where 條件(<all 子查詢語句);
  > select 
      *
    from 
      student 
    where 
      age < all (select 
                   age 
                 from 
                   student 
                 where 
                   class = "one"
                )
    order by age asc;
  
      +----+----------+------+-------+-------+---------+
      | no | name     | age  | score | class | address |
      +----+----------+------+-------+-------+---------+
      |  7 | xiao bai |   17 |    79 | three | NULL    |
      +----+----------+------+-------+-------+---------+
      1 row in set (0.00 sec)

  • from 子查詢

  # 查詢單表記錄，from 多行多列子查詢，通常看成一張臨時表的方式來處理
  # select 字段名 from 表名1 內/外鏈接表子查詢語句;
  > select 
      B.bno, B.bname, B.bano, C.aname 
    from 
      B, (
           select ano, aname, loc from A where ano < 2
         ) C
    where 
      B.bano = C.ano;
  
      +-----+----------+------+-----------+
      | bno | bname    | bano | aname     |
      +-----+----------+------+-----------+
      |   0 | zhangsan |    0 | 研發部    |
      +-----+----------+------+-----------+
      1 row in set (0.00 sec)

4.2 查詢多表記錄

• 當須要同時顯示多個表中的字段時，就能夠用錶鏈接來實現這樣的功能。

• 從大致上分，錶鏈接分爲內鏈接和外鏈接，它們之間最主要的區別是，內鏈接僅選出兩張表中互相匹配的記錄，而外鏈接會選出其它不匹配的記錄。

• 1）多表聯合查詢

  # 查詢多表記錄，多表聯合查詢，必定要有表於表之間的關聯字段
  # select 字段名 from 表名1, 表名2 where 關聯條件;
  > select 
      B.bno, B.bname, B.bano, A.aname 
    from 
      B, A 
    where 
      B.bano = A.ano; 
  
      +-----+----------+------+-----------+
      | bno | bname    | bano | aname     |
      +-----+----------+------+-----------+
      |   0 | zhangsan |    0 | 研發部     |
      |   1 | lisi     |    2 | 銷售部     |
      +-----+----------+------+-----------+
      2 rows in set (0.00 sec)

• 2）內聯查詢

  # 查詢多表記錄，內鏈接查詢
  # select 字段名 from 表名1 inner join 表名2 on 關聯條件;
  > select 
      B.bno, B.bname, B.bano, A.aname 
    from 
      B 
    inner join 
      A 
    on 
      B.bano = A.ano;
  
      +-----+----------+------+-----------+
      | bno | bname    | bano | aname     |
      +-----+----------+------+-----------+
      |   0 | zhangsan |    0 | 研發部     |
      |   1 | lisi     |    2 | 銷售部     |
      +-----+----------+------+-----------+
      2 rows in set (0.00 sec)

• 3）外聯查詢

  # 查詢多表記錄，左外鏈接查詢，包含全部的左表中的記錄甚至是右表中沒有和它匹配的記錄
  # select 字段名 from 表名1 left outer join 表名2 on 關聯條件;
  > select 
      B.bno, B.bname, B.bano, A.aname
    from 
      B 
    left outer join 
      A 
    on 
      B.bano = A.ano;
  
      +-----+----------+------+-----------+
      | bno | bname    | bano | aname     |
      +-----+----------+------+-----------+
      |   0 | zhangsan |    0 | 研發部     |
      |   1 | lisi     |    2 | 銷售部     |
      |   2 | wangwu   | NULL | NULL      |
      +-----+----------+------+-----------+
      3 rows in set (0.00 sec)

  # 查詢多表記錄，右外鏈接查詢，包含全部的右表中的記錄甚至是左表中沒有和它匹配的記錄
  # select 字段名 from 表名1 left outer join 表名2 on 關聯條件;
  > select 
      B.bno, B.bname, B.bano, A.aname
    from 
      B 
    right outer join 
      A 
    on 
      B.bano = A.ano
    order by
      bno asc;
  
      +------+----------+------+-----------+
      | bno  | bname    | bano | aname     |
      +------+----------+------+-----------+
      | NULL | NULL     | NULL | 財務部     |
      |    0 | zhangsan |    0 | 研發部     |
      |    1 | lisi     |    2 | 銷售部     |
      +------+----------+------+-----------+
      3 rows in set (0.00 sec)

  # 查詢多表記錄，全外鏈接查詢，包含全部的左表和右表中的記錄甚至是沒有匹配的記錄
  # MySQL 是不支持全外的鏈接的，這裏給出的寫法適合 Oracle 和 DB2
  # select 字段名 from 表名1 left outer join 表名2 on 關聯條件;
  > select 
      B.bno, B.bname, B.bano, A.aname
    from 
      B 
    full outer join 
      A 
    on 
      B.bano = A.ano
    order by
      bno asc;

• 4）記錄聯合查詢

  • 咱們常常會碰到這樣的應用，將兩個表的數據按照必定的查詢條件查詢出來後，將結果合併到一塊兒顯示出來。
  • 這個時候，就須要用 union 和 union all 關鍵字來實現這樣的功能。
  • union all 會把結果直接合並在一塊兒，union 會將合併後的結果進行一次 distinct 去除重複的記錄。

  # 查詢多表記錄，記錄聯合查詢
  # select 字段名 from 表名1 
    union | union all
    select 字段名 from 表名2;
  > select ano, aname, loc from A union all select bno, bname, bano from B;
  
      +-----+-----------+------+
      | ano | aname     | loc  |
      +-----+-----------+------+
      |   0 | 研發部     | aaaa |
      |   1 | 財務部     | bbbb |
      |   2 | 銷售部     | cccc |
      |   0 | zhangsan  | 0    |
      |   1 | lisi      | 2    |
      |   2 | wangwu    | NULL |
      +-----+-----------+------+
      6 rows in set (0.00 sec)