Getting first record from two tables
I am looking to get the first date with the customer and item description from the following example table
To create my example
CREATE TABLE cust
(
CUSTNO int,
ENAME varchar(50)
)
CREATE TABLE orders
(
CUSTNO int,
Description varchar(50),
ORDERDATE date
)
INSERT INTO cust VALUES (7369, 'SMITH');
INSERT INTO cust VALUES (7499, 'ALLEN');
INSERT INTO cust VALUES (7521, 'WARD');
INSERT INTO cust VALUES (7566, 'JONES');
INSERT INTO cust VALUES (7654, 'MARTIN');
INSERT INTO cust VALUES (7698, 'BLAKE');
INSERT INTO cust VALUES (7782, 'CLARK');
INSERT INTO cust VALUES (7788, 'SCOTT');
INSERT INTO cust VALUES (7839, 'KING');
INSERT INTO cust VALUES (7844, 'TURNER');
INSERT INTO cust VALUES (7876, 'ADAMS');
INSERT INTO cust VALUES (7900, 'JAMES');
INSERT INTO cust VALUES (7902, 'FORD');
INSERT INTO cust VALUES (7934, 'MILLER');
INSERT INTO orders VALUES (7782, 'Something','17-DEC-1980');
INSERT INTO orders VALUES (7782, 'Something else', '17-DEC-2000');
INSERT INTO orders VALUES (7900, 'Something', '17-DEC-1980');
INSERT INTO orders VALUES (7900, 'Something else','17-DEC-1990');
INSERT INTO orders VALUES (7934, 'Something','17-DEC-1980');
Was trying something like this
select [EN开发者_StackOverflow中文版AME],[cust].[CUSTNO], MIN([ORDERDATE]),[Description]
from [cust],[orders]
where [cust].[CUSTNO]=[orders].[CUSTNO]
group by [cust].[CUSTNO],[ENAME],[Description]
My problem is this returns too many rows. I just want to see each customer and then list there first date (blank or null if there is no order).
Any ideas?
with MinOrder as (
select
custno, min(orderdate) orderdate
from [orders]
GROUP BY custno)
select [ENAME],[cust].[CUSTNO], o.[orderdate], [Description]
from
cust
LEFT JOIN orders o
ON cust.custNo = o.custno
LEFT JOiN MinOrder mo
ON mo.orderdate = o.orderdate
and mo.custno = o.custno
If you can't use a CTE you can use a inline view instead
select [ENAME],[cust].[CUSTNO], o.[orderdate], [Description]
from
cust
LEFT JOIN orders o
ON cust.custNo = o.custno
LEFT JOiN ( select
custno, min(orderdate) orderdate
from [orders]
GROUP BY custno) mo
ON mo.orderdate = o.orderdate
and mo.custno = o.custno
SELECT c.[ENAME],c.[CUSTNO], o.[orderdate], o.[Description]
FROM cust c
LEFT JOIN orders o
ON c.custNo = o.custno
LEFT JOIN
( SELECT custno, min(orderdate) orderdate
FROM [orders]
GROUP BY custno) mo
ON mo.orderdate = o.orderdate
AND mo.custno = o.custno
You need the left joins to get the order if one exists but still get the customer if no orders exist. @conrad Frix's solution will work as well, but I incuded this in case you use a database that doesn't accept the with statement.
In the future, you should stop writing implict joins (using a comma to separate the tables and putting the join conditions inteh where clause). They are a bad programming techinique and contribute to why you don't understand joins correctly (or you would have known to use a left join).
;with cteMinOrder as (
select [CUSTNO], MIN([ORDERDATE]) as minDate
from [orders]
group by [CUSTNO]
)
select [ENAME],[cust].[CUSTNO], mo.minDate, [Description]
from [cust]
left join cteMinOrder mo
on [cust].[CUSTNO]=mo.[CUSTNO]
left join [orders]
on [cust].[CUSTNO]=[orders].[CUSTNO]
and mo.minDate = [orders].[ORDERDATE]
select [ENAME],[cust].[CUSTNO],[minorderdate],[Description]
from
[cust]
left join
select [CUSTNO],MIN([ORDERDATE]) AS minorderdate
from [orders]
group by [CUSTNO] as t
on [cust].[CUSTNO] = [t].[CUSTNO];
Syntax might need tweaking depending on the actual dialect you're using, but that relation should do what you want.
Just omit [ENAME]
and [Description]
from the GROUP BY
clause
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