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Left Outer Join Not Working?
(4 answers)
Closed 4 years ago.
I've created a table of students with columns student_id as primary key,
student_name and gender.
I've an another table gender which consists of gender_id and gender.
gender_id in student refers to table gender.
Tables data looks like this:
Student table
STUDENT_ID STUDENT_NAME GENDER
1 Ajith 1
2 Alan 1
3 Ann 2
4 Alexa 2
5 Amith 1
6 Nisha 2
7 Rathan 1
8 Rebecca 2
9 asdf null
10 asd null
11 dbss null
Gender Table
GENDER_ID GENDER
1 Male
2 Female
3 Others
My query and its result
SELECT S.STUDENT_NAME,
G.GENDER
FROM STUDENTS S
FULL OUTER JOIN GENDER G ON G.GENDER_ID = S.GENDER
result is giving with 12 rows including the Others value from the gender table.
STUDENT_ID STUDENT_NAME GENDER
1 Ajith Male
2 Alan Male
3 Ann Female
4 Alexa Female
5 Amith Male
6 Nisha Female
7 Rathan Male
8 Rebecca Female
Others
9 asdf
10 asd
11 dbss
I'm trying to restrict a particular student_id:
SELECT S.STUDENT_ID,
S.STUDENT_NAME,
G.GENDER
FROM STUDENTS S
FULL OUTER JOIN GENDER G ON G.GENDER_ID = S.GENDER
WHERE S.STUDENT_ID <> 11;
now the the total number of the rows are reduced to 10.
STUDENT_ID STUDENT_NAME GENDER
1 Ajith Male
2 Alan Male
3 Ann Female
4 Alexa Female
5 Amith Male
6 Nisha Female
7 Rathan Male
8 Rebecca Female
9 asdf
10 asd
Why has the one row with Others Values disappeared from the second select query?
I'm trying to find the cause of this issue.
That's because NULL <> 11 is not TRUE, but NULL, and only rows where the condition is TRUE are included in the result.
You'd have to write something like
WHERE s.student_id IS DISTINCT FROM 11
Your second select query returns all rows where student_id is different (<>) from 11.
I can't explain my problem in English well. So I write my problem in a personal way.
user_id name surname
1 john great
2 mary white
3 joseph alann
event_id official_id assistant_id date
1 1 2 2017-12-19
2 1 3 2017-12-20
3 2 3 2017-12-21
I want to get names at the same time when I query an event. I tried:
SELECT * FROM event a, user b WHERE a.official_id=b.user_id AND a.assistant_id=b.user_id
When I use "OR" instead of "AND" gives me cartesian result. I want the result like:
event_id off_id off_name asst_id asst_name date
1 1 john 2 mary 2017-12-19
2 1 john 3 joseph 2017-12-20
3 2 mary 3 joseph 2017-12-21
In my Table 1, It may have AND have a null entry in the address column to corresponding record OR not have a matching entry in Table 2.
I want to present all the records in Table 1 but also present corresponding entries from Table 2. My RESULT is what I am trying to achieve.
Table 1
ID First Last
1 John Smith
2 Bob Long
3 Bill Davis
4 Sam Bird
5 Tom Fenton
6 Mary Willis
Table 2
RefID ID Address
1 1 123 Main
2 2 555 Center
3 3 626 Smith
4 4 412 Walnut
5 1
6 2 555 Center
7 3
8 4 412 Walnut
Result
Id First Last Address
1 John Smith 123 Main
2 Bob Long 555 Center
3 Bill Davis 626 Smith
4 Sam Bird 412 Walnut
5 Tom Fenton
6 Mary Willis
You need an outer join for this:
SELECT * FROM Table1 t1 LEFT OUTER JOIN Table2 t2 ON t1.ID = t2.RefID
How do you join those two tables? If table 2 have more than 1 matched address, how do you want display them? Please clarify in your question.
Here is a query based on my assumptions.
SELECT
ID, First, Last,
Address = (SELECT MAX(Address) FROM Table2 t2 WHERE t1.ID = t2.ID)
FROM Table1 t1
I have a table with following data:
Id Name Value
1 John 100
2 John -500
3 John 500
4 Smith 10
5 Smith 20
6 Smith -20
7 Stuart -10
8 Wills 25
I am looking for an efficient TSQL query which can remove John -500 and Smith -20 (i.e. records with negative value if they have a similar positive value in the same group [group by names]).
I think this is what you need. (SQL DEMO)
delete y
from mytable y join (
select id,name, value
from mytable x
where value > 0) z on y.name = z.name and y.value = -1 * z.value
select * from mytable
--SELECT RESULTS AFTER DELETING
ID NAME VALUE
1 John 100
3 John 500
4 Smith 10
5 Smith 20
7 Stuart -10
8 Wills 25
delete a
from mytable a
join mytable b
on b.name = a.name
and a.value < 0
and b.value = -1 * z.value
Almost the same as Kaf +1
I have a problem with a t-sql query.
Let's say I have a categories tree (categories ID)
cat_table
1
|
2-\
| 3-\
6 | 5
| 4 |
... ...
ads_table
ad_ID
category_ID
of course the category_ID column references to the ID column in the cat_table
the problem is, how to get (recursive ?) all advertisements from all categories which the top-most parent is the 1st category?
try using a recursive Common Table Expressions, aka "CTE" (available in SQL Server 2005 and up) like this:
--go through a nested table supervisor - user table and display the chain
DECLARE #Contacts table (id varchar(6), first_name varchar(10), reports_to_id varchar(6))
INSERT #Contacts VALUES ('1','Jerome', NULL ) -- tree is as follows:
INSERT #Contacts VALUES ('2','Joe' ,'1') -- 1-Jerome
INSERT #Contacts VALUES ('3','Paul' ,'2') -- / \
INSERT #Contacts VALUES ('4','Jack' ,'3') -- 2-Joe 9-Bill
INSERT #Contacts VALUES ('5','Daniel','3') -- / \ \
INSERT #Contacts VALUES ('6','David' ,'2') -- 3-Paul 6-David 10-Sam
INSERT #Contacts VALUES ('7','Ian' ,'6') -- / \ / \
INSERT #Contacts VALUES ('8','Helen' ,'6') -- 4-Jack 5-Daniel 7-Ian 8-Helen
INSERT #Contacts VALUES ('9','Bill ' ,'1') --
INSERT #Contacts VALUES ('10','Sam' ,'9') --
DECLARE #Root_id char(4)
--get 2 and below
SET #Root_id=2
PRINT '#Root_id='+COALESCE(''''+#Root_id+'''','null')
;WITH StaffTree AS
(
SELECT
c.id, c.first_name, c.reports_to_id, c.reports_to_id as Manager_id, cc.first_name AS Manager_first_name, 1 AS LevelOf
FROM #Contacts c
LEFT OUTER JOIN #Contacts cc ON c.reports_to_id=cc.id
WHERE c.id=#Root_id OR (#Root_id IS NULL AND c.reports_to_id IS NULL)
UNION ALL
SELECT
s.id, s.first_name, s.reports_to_id, t.id, t.first_name, t.LevelOf+1
FROM StaffTree t
INNER JOIN #Contacts s ON t.id=s.reports_to_id
WHERE s.reports_to_id=#Root_id OR #Root_id IS NULL OR t.LevelOf>1
)
SELECT * FROM StaffTree
output:
#Root_id='2 '
id first_name reports_to_id Manager_id Manager_first_name LevelOf
------ ---------- ------------- ---------- ------------------ -----------
2 Joe 1 1 Jerome 1
3 Paul 2 2 Joe 2
6 David 2 2 Joe 2
7 Ian 6 6 David 3
8 Helen 6 6 David 3
4 Jack 3 3 Paul 3
5 Daniel 3 3 Paul 3
(7 row(s) affected)
change #Root_id to get different output:
#Root_id=null
id first_name reports_to_id Manager_id Manager_first_name LevelOf
------ ---------- ------------- ---------- ------------------ -----------
1 Jerome NULL NULL NULL 1
2 Joe 1 1 Jerome 2
9 Bill 1 1 Jerome 2
10 Sam 9 9 Bill 3
3 Paul 2 2 Joe 3
6 David 2 2 Joe 3
7 Ian 6 6 David 4
8 Helen 6 6 David 4
4 Jack 3 3 Paul 4
5 Daniel 3 3 Paul 4
(10 row(s) affected)
There is an option to avoid recurrency in tree browsing queries. You can add 'Path' column to your categories tree. It should contain each element ancestors IDs delimited with some non-numeric character (like slash).
For example your "ID=4" category's path would look like that: "/1/2/3/"
Now when you join your ads table to categories you need to do following:
select * from ads_table
inner join cat_table on cat_table.ID = ads_table.category_ID
where cat_table.Path like '/1/%'
And that's your query.
You can read more on this topic on my blog post
Are you familiar with Common Table Expressions in SQL Server? One of the many uses a CTE has is to do recursive queries.
The following is one of the best articles I've found on the subject:
https://web.archive.org/web/20210927200924/http://www.4guysfromrolla.com/webtech/071906-1.shtml