[英]SQL using two subqueries
我正在学习SQL子查询。 这是我在书中使用的子查询:
SELECT account_id, product_cd, cust_id
FROM account
WHERE open_branch_id = (
SELECT branch_id
FROM branch
WHERE name = 'Woburn Branch'
) AND open_emp_id IN (
SELECT emp_id
FROM employee
WHERE title = 'Teller' OR title = 'Head Teller'
);
结果:
+------------+------------+---------+
| account_id | product_cd | cust_id |
+------------+------------+---------+
| 1 | CHK | 1 |
| 2 | SAV | 1 |
| 3 | CD | 1 |
| 4 | CHK | 2 |
| 5 | SAV | 2 |
| 17 | CD | 7 |
| 27 | BUS | 11 |
+------------+------------+---------+
我查看了这个查询,试图解释并理解它以及它的子句背后的原因,但是,我无法理解最后一个AND
子句AND open_emp_id IN
...
我注意到
SELECT account_id, product_cd, cust_id
FROM account
WHERE open_branch_id = (
SELECT branch_id
FROM branch
WHERE name = 'Woburn Branch'
)
您得到与上述相同的结果。 谁能向我解释最后一个AND open_emp_id IN
子句背后的AND open_emp_id IN
,以及省略它会如何影响最终结果?
子查询中使用的表:
帐户表
+------------+------------+---------+------------+------------+--------------------+--------+----------------+-------------+---------------+-----------------+
| account_id | product_cd | cust_id | open_date | close_date | last_activity_date | status | open_branch_id | open_emp_id | avail_balance | pending_balance |
+------------+------------+---------+------------+------------+--------------------+--------+----------------+-------------+---------------+-----------------+
| 1 | CHK | 1 | 2000-01-15 | NULL | 2005-01-04 | ACTIVE | 2 | 10 | 1057.75 | 1057.75 |
| 2 | SAV | 1 | 2000-01-15 | NULL | 2004-12-19 | ACTIVE | 2 | 10 | 500.00 | 500.00 |
| 3 | CD | 1 | 2004-06-30 | NULL | 2004-06-30 | ACTIVE | 2 | 10 | 3000.00 | 3000.00 |
| 4 | CHK | 2 | 2001-03-12 | NULL | 2004-12-27 | ACTIVE | 2 | 10 | 2258.02 | 2258.02 |
| 5 | SAV | 2 | 2001-03-12 | NULL | 2004-12-11 | ACTIVE | 2 | 10 | 200.00 | 200.00 |
| 7 | CHK | 3 | 2002-11-23 | NULL | 2004-11-30 | ACTIVE | 3 | 13 | 1057.75 | 1057.75 |
| 8 | MM | 3 | 2002-12-15 | NULL | 2004-12-05 | ACTIVE | 3 | 13 | 2212.50 | 2212.50 |
| 10 | CHK | 4 | 2003-09-12 | NULL | 2005-01-03 | ACTIVE | 1 | 1 | 534.12 | 534.12 |
| 11 | SAV | 4 | 2000-01-15 | NULL | 2004-10-24 | ACTIVE | 1 | 1 | 767.77 | 767.77 |
| 12 | MM | 4 | 2004-09-30 | NULL | 2004-11-11 | ACTIVE | 1 | 1 | 5487.09 | 5487.09 |
| 13 | CHK | 5 | 2004-01-27 | NULL | 2005-01-05 | ACTIVE | 4 | 16 | 2237.97 | 2897.97 |
| 14 | CHK | 6 | 2002-08-24 | NULL | 2004-11-29 | ACTIVE | 1 | 1 | 122.37 | 122.37 |
| 15 | CD | 6 | 2004-12-28 | NULL | 2004-12-28 | ACTIVE | 1 | 1 | 10000.00 | 10000.00 |
| 17 | CD | 7 | 2004-01-12 | NULL | 2004-01-12 | ACTIVE | 2 | 10 | 5000.00 | 5000.00 |
| 18 | CHK | 8 | 2001-05-23 | NULL | 2005-01-03 | ACTIVE | 4 | 16 | 3487.19 | 3487.19 |
| 19 | SAV | 8 | 2001-05-23 | NULL | 2004-10-12 | ACTIVE | 4 | 16 | 387.99 | 387.99 |
| 21 | CHK | 9 | 2003-07-30 | NULL | 2004-12-15 | ACTIVE | 1 | 1 | 125.67 | 125.67 |
| 22 | MM | 9 | 2004-10-28 | NULL | 2004-10-28 | ACTIVE | 1 | 1 | 9345.55 | 9845.55 |
| 23 | CD | 9 | 2004-06-30 | NULL | 2004-06-30 | ACTIVE | 1 | 1 | 1500.00 | 1500.00 |
| 24 | CHK | 10 | 2002-09-30 | NULL | 2004-12-15 | ACTIVE | 4 | 16 | 23575.12 | 23575.12 |
| 25 | BUS | 10 | 2002-10-01 | NULL | 2004-08-28 | ACTIVE | 4 | 16 | 0.00 | 0.00 |
| 27 | BUS | 11 | 2004-03-22 | NULL | 2004-11-14 | ACTIVE | 2 | 10 | 9345.55 | 9345.55 |
| 28 | CHK | 12 | 2003-07-30 | NULL | 2004-12-15 | ACTIVE | 4 | 16 | 38552.05 | 38552.05 |
| 29 | SBL | 13 | 2004-02-22 | NULL | 2004-12-17 | ACTIVE | 3 | 13 | 50000.00 | 50000.00 |
+------------+------------+---------+------------+------------+--------------------+--------+----------------+-------------+---------------+-----------------+
分支表:
+-----------+---------------+----------------------+---------+-------+-------+
| branch_id | name | address | city | state | zip |
+-----------+---------------+----------------------+---------+-------+-------+
| 1 | Headquarters | 3882 Main St. | Waltham | MA | 02451 |
| 2 | Woburn Branch | 422 Maple St. | Woburn | MA | 01801 |
| 3 | Quincy Branch | 125 Presidential Way | Quincy | MA | 02169 |
| 4 | So. NH Branch | 378 Maynard Ln. | Salem | NH | 03079 |
+-----------+---------------+----------------------+---------+-------+-------+
员工表:
+--------+----------+-----------+------------+----------+-----------------+---------+--------------------+--------------------+
| emp_id | fname | lname | start_date | end_date | superior_emp_id | dept_id | title | assigned_branch_id |
+--------+----------+-----------+------------+----------+-----------------+---------+--------------------+--------------------+
| 1 | Michael | Smith | 2005-06-22 | NULL | NULL | 3 | President | 1 |
| 2 | Susan | Barker | 2006-09-12 | NULL | 1 | 3 | Vice President | 1 |
| 3 | Robert | Tyler | 2005-02-09 | NULL | 1 | 3 | Treasurer | 1 |
| 4 | Susan | Hawthorne | 2006-04-24 | NULL | 3 | 1 | Operations Manager | 1 |
| 5 | John | Gooding | 2007-11-14 | NULL | 4 | 2 | Loan Manager | 1 |
| 6 | Helen | Fleming | 2008-03-17 | NULL | 4 | 1 | Head Teller | 1 |
| 7 | Chris | Tucker | 2008-09-15 | NULL | 6 | 1 | Teller | 1 |
| 8 | Sarah | Parker | 2006-12-02 | NULL | 6 | 1 | Teller | 1 |
| 9 | Jane | Grossman | 2006-05-03 | NULL | 6 | 1 | Teller | 1 |
| 10 | Paula | Roberts | 2006-07-27 | NULL | 4 | 1 | Head Teller | 2 |
| 11 | Thomas | Ziegler | 2004-10-23 | NULL | 10 | 1 | Teller | 2 |
| 12 | Samantha | Jameson | 2007-01-08 | NULL | 10 | 1 | Teller | 2 |
| 13 | John | Blake | 2004-05-11 | NULL | 4 | 1 | Head Teller | 3 |
| 14 | Cindy | Mason | 2006-08-09 | NULL | 13 | 1 | Teller | 3 |
| 15 | Frank | Portman | 2007-04-01 | NULL | 13 | 1 | Teller | 3 |
| 16 | Theresa | Markham | 2005-03-15 | NULL | 4 | 1 | Head Teller | 4 |
| 17 | Beth | Fowler | 2006-06-29 | NULL | 16 | 1 | Teller | 4 |
| 18 | Rick | Tulman | 2006-12-12 | NULL | 16 | 1 | Teller | 4 |
+--------+----------+-----------+------------+----------+-----------------+---------+--------------------+--------------------+
AND open_emp_id IN子句仅选择标题为“ Teller”或“ Head Teller”的员工ID。 在您的情况下,结果并没有什么不同,因为您要查找名称为“ Woburn Branch”的分支,并且所有的员工都只有“ Teller”或“ Head Teller”职称只是一个巧合。
| 10 | Paula | Roberts | 2006-07-27 | NULL | 4 | 1 | Head Teller | 2 |
| 11 | Thomas | Ziegler | 2004-10-23 | NULL | 10 | 1 | Teller | 2 |
| 12 | Samantha | Jameson | 2007-01-08 | NULL | 10 | 1 | Teller | 2 |
在第一个查询中将分支名称更改为“总部”,您将看到子查询的不同之处。 没有“头衔”或“总柜员”头衔的“总部”员工将被排除在外。
最后一个AND将选择标准缩小为仅包括由出纳员或总出纳员开设的账户。 如果贷款经理或运营经理已开设该帐户,则将其排除在外。
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