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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.
Related
I have two tables:
table_a
id name
1 john
2 dave
3 tim
4 marta
5 jim
table_b
id sum random_metric
1 10.50 abc
3 11.5 efg
5 5.76 ghj
I have joined them on id
SELECT ...
FROM table_a
LEFT JOIN table_b ON table_a.id = table_b.id
and I get:
id name sum random_metric
1 john 10.5 abc
2 dave
3 tim 11.5 efg
4 marta
5 jim 5.76 ghj
Then I want to convert the sum column to double precision but since it has empty strings in rows 2, 4 it does not work.
How could I join tables so that I would have this:
id name sum random_metric
1 john 10.5 abc
2 dave NULL NULL
3 tim 11.5 efg
4 marta NULL NULL
5 jim 5.76 ghj
I have a table with answers regarding different questions, all of them numbered. There are basically these columns: IdAnswer (unique for each answer in the table), IdUser (which won't repeat even if the same user answer questions a second time), IdQuestion and Answer.
IdAnswer IdUser IdQuestion Answer
1 John 1 0
2 John 4 1
3 John 5 1
4 John 6 0
5 Bob 1 1
6 Bob 3 1
7 Bob 5 0
8 Mark 2 0
9 Mark 7 1
10 Mark 5 0
I'd like to select from this table all answers to a specific question (say, IdQuestion = 5), and also the last question each user answered just before question number 5.
In the end I need a table that should look like this:
IdAnswer IdUser IdQuestion Answer
2 John 4 1
3 John 5 1
6 Bob 3 1
7 Bob 5 0
9 Mark 7 1
10 Mark 5 0
I've managed to make this work using a cursor to iterate through each line from the first SELECT result (which filters by IdQuestion), but I'm not sure if this is the best (and fastest) way of doing it. Is there any more efficient way of achieving the same result?
And by the way, I'm using SQL Server Management Studio 2012.
Here is one way using LEAD function
select * from
(
select *,NextQ = Lead(IdQuestion)over(partition by IdUser order by IdAnswer)
from youtable
) a
Where 5 in (IdQuestion, NextQ )
for older versions
;WITH cte
AS (SELECT prev_id = Min(CASE WHEN IdQuestion = 5 THEN rn - 1 END) OVER( partition BY IdUser),*
FROM (SELECT rn = Row_number()OVER(partition BY IdUser ORDER BY IdAnswer),*
FROM Yourtable)a)
SELECT *
FROM cte
WHERE rn IN ( prev_id, prev_id + 1 )
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 2 tables in sql table_a and table_b this is the output: (1 to many relationship)
table_a table_b
id_no (pk) name id_no (fk) id_tabl(pk) order_code order_item
1 a 1 1 11 aple
1 a 1 2 12 orange
1 a 1 3 13 ice
2 b 2 4 12 orange
2 b 2 5 13 ice
3 c 3 6 13 ice
3 c 3 7 12 orange
3 c 3 8 11 aple
I want to display only 1 name with all his order_item.
How can I display it using iReport in the xml?
The output sample:
id_no name order_item
1 a aple
orange
ice
2 b orange
ice
3 c ice
orange
aple
Using only 2 (order_item) field pattern in every pages of my invoice
the other display will be displayed in invoice pages 2.
You should use Data Grouping.
You can read this article about data grouping.
Your can use the query like this:
SELECT table_a.id_no, table_a.name, table_b.order_item FROM table_a, table_b WHERE table_a.id_no=table_b.id_no ORDER BY table_a.name
Note: may be you need to add sort by table_a.id_no column.
You should create the iReport's group for the name field
Note: may be you need to create two groups - for id_no and name fields.
You can use the Group and Details bands for drawing the data row. Or you can put all textField elements to the Detail band. In this case you should set false value to the isPrintRepeatedValues textField's property (for id_no and name fields).