mysql加载顺序
手写顺序
SELECT DISTINCT
<select list>
FROM
<left_table> join <join_type> JOIN <right_table> ON <join_condition>
WHERE
<where_condition>
GROUP BY
<group_by_list>
HAVING
<having_condition>
ORDER BY
<order_by_condition>
LIMIT <limit_number>
机读顺序
1. FROM <left_table>
2. ON <join_condition>
3. <join_type> JOIN <right_table>
4. WHERE <where_condition>
5. GROUP BY <group_by_list>
6. HAVING <having_condition>
7. SELECT
8. DISTINCT <select list>
9. ORDER BY <order_by_condition>
10. LIMIT <limit_number>
sql语句的执行顺序可以用这张鱼骨图来表示
join连表
mysql中的连表基本可以分为以下几种。
接下来对这几种写出相应的sql语句。
首先是创建相应的表来进行实践。
create table if not exists tbl_dept(
id int not null auto_increment primary key,
deptName varchar(30),
locAdd varchar(40)
);
create table if not exists tbl_emp(
id int auto_increment primary key,
name varchar(20),
depid int
);
insert into tbl_dept(deptName, locAdd) values(\'RD\', 11);
insert into tbl_dept(deptName, locAdd) values(\'HR\', 12);
insert into tbl_dept(deptName, locAdd) values(\'MK\', 13);
insert into tbl_dept(deptName, locAdd) values(\'MIS\', 14);
insert into tbl_dept(deptName, locAdd) values(\'FD\', 15);
insert into tbl_emp(name, depid) values(\'z3\', 1);
insert into tbl_emp(name, depid) values(\'z4\', 1);
insert into tbl_emp(name, depid) values(\'z5\', 1);
insert into tbl_emp(name, depid) values(\'w5\', 2);
insert into tbl_emp(name, depid) values(\'w6\', 2);
insert into tbl_emp(name, depid) values(\'s7\', 3);
insert into tbl_emp(name, depid) values(\'s8\', 4);
insert into tbl_emp(name, depid) values(\'s9\', 51);
内连接(等值连接)
mysql> select * from tbl_emp as e inner join tbl_dept as d on e.depid=d.id;
+----+------+-------+----+----------+--------+
| id | name | depid | id | deptName | locAdd |
+----+------+-------+----+----------+--------+
| 1 | z3 | 1 | 1 | RD | 11 |
| 2 | z4 | 1 | 1 | RD | 11 |
| 3 | z5 | 1 | 1 | RD | 11 |
| 4 | w5 | 2 | 2 | HR | 12 |
| 5 | w6 | 2 | 2 | HR | 12 |
| 6 | s7 | 3 | 3 | MK | 13 |
| 7 | s8 | 4 | 4 | MIS | 14 |
+----+------+-------+----+----------+--------+
7 rows in set (0.01 sec)
左连接(连接左表的全部，右表缺失的字段以null补齐)
mysql> select * from tbl_emp as e left join tbl_dept as d on e.depid=d.id;
+----+------+-------+------+----------+--------+
| id | name | depid | id | deptName | locAdd |
+----+------+-------+------+----------+--------+
| 1 | z3 | 1 | 1 | RD | 11 |
| 2 | z4 | 1 | 1 | RD | 11 |
| 3 | z5 | 1 | 1 | RD | 11 |
| 4 | w5 | 2 | 2 | HR | 12 |
| 5 | w6 | 2 | 2 | HR | 12 |
| 6 | s7 | 3 | 3 | MK | 13 |
| 7 | s8 | 4 | 4 | MIS | 14 |
| 8 | s9 | 51 | NULL | NULL | NULL |
+----+------+-------+------+----------+--------+
8 rows in set (0.03 sec)
右连接(连接右表的全部，左表缺失的字段以null补齐)
mysql> select * from tbl_emp as e right join tbl_dept as d on e.depid=d.id;
+------+------+-------+----+----------+--------+
| id | name | depid | id | deptName | locAdd |
+------+------+-------+----+----------+--------+
| 1 | z3 | 1 | 1 | RD | 11 |
| 2 | z4 | 1 | 1 | RD | 11 |
| 3 | z5 | 1 | 1 | RD | 11 |
| 4 | w5 | 2 | 2 | HR | 12 |
| 5 | w6 | 2 | 2 | HR | 12 |
| 6 | s7 | 3 | 3 | MK | 13 |
| 7 | s8 | 4 | 4 | MIS | 14 |
| NULL | NULL | NULL | 5 | FD | 15 |
+------+------+-------+----+----------+--------+
8 rows in set (0.03 sec)
左独占连接
mysql> select * from tbl_emp as e left join tbl_dept as d on e.depid=d.id where d.id is null;
+----+------+-------+------+----------+--------+
| id | name | depid | id | deptName | locAdd |
+----+------+-------+------+----------+--------+
| 8 | s9 | 51 | NULL | NULL | NULL |
+----+------+-------+------+----------+--------+
1 row in set (0.04 sec)
右独占连接
mysql> select * from tbl_emp as e right join tbl_dept as d on e.depid=d.id where e.id is null;
+------+------+-------+----+----------+--------+
| id | name | depid | id | deptName | locAdd |
+------+------+-------+----+----------+--------+
| NULL | NULL | NULL | 5 | FD | 15 |
+------+------+-------+----+----------+--------+
1 row in set (0.04 sec)
全连接
由于 mysql中不支持全连接，所以需要使用union来进行模拟。
mysql> select * from tbl_emp as e left join tbl_dept as d on e.depid=d.id
union
select * from tbl_emp as e right join tbl_dept as d on e.depid=d.id;
+------+------+-------+------+----------+--------+
| id | name | depid | id | deptName | locAdd |
+------+------+-------+------+----------+--------+
| 1 | z3 | 1 | 1 | RD | 11 |
| 2 | z4 | 1 | 1 | RD | 11 |
| 3 | z5 | 1 | 1 | RD | 11 |
| 4 | w5 | 2 | 2 | HR | 12 |
| 5 | w6 | 2 | 2 | HR | 12 |
| 6 | s7 | 3 | 3 | MK | 13 |
| 7 | s8 | 4 | 4 | MIS | 14 |
| 8 | s9 | 51 | NULL | NULL | NULL |
| NULL | NULL | NULL | 5 | FD | 15 |
+------+------+-------+------+----------+--------+
9 rows in set (0.04 sec)
左独占连接+右独占连接
同理使用union连接来进行模拟
mysql> select * from tbl_emp as e left join tbl_dept as d on e.depid=d.id where d.id is null
union
select * from tbl_emp as e right join tbl_dept as d on e.depid=d.id where e.id is null;
+------+------+-------+------+----------+--------+
| id | name | depid | id | deptName | locAdd |
+------+------+-------+------+----------+--------+
| 8 | s9 | 51 | NULL | NULL | NULL |
| NULL | NULL | NULL | 5 | FD | 15 |
+------+------+-------+------+----------+--------+
2 rows in set (0.04 sec)