Table1
...
LogEntryID *PrimaryKey*
Value
ThresholdID - - - Link to the appropriate threshold being applied to this log entry.
...
Table2
...
ThresholdID *PrimaryKey*
Threshold
...
All fields are integers.
The "..." thingies are there to show that these tables hold a lot more imformation than just this. They are set up this way for a reason, and I can't change it at this point.
I need write a SQL statement to select every record from Table1 where the Value field in that particular log record is less than the Threshold field in the linked record of Table2.
I'm newish to SQL, so I know this is a basic question.
If anyone can show me how this SQL statement would be structured, it would be greatly appreciated.
SELECT T1.*
FROM Table1 T1
JOIN Table2 T2 ON T2.ThresholdID = T1.ThresholdID
WHERE T2.Threshold > T1.Value
SELECT t1.*
FROM dbo.Table1 t1 INNER JOIN dbo.Table2 t2 ON t1.ThresholdID = t2.ThresholdID
WHERE t2.Threshold > t1.Value
SELECT * from table1 t1 join table2 t2 on (t1.thresholdId = t2.thresholdId)
where t1.value < t2.threshold;
SELECT t1.LogEntryID, t1.Value, t1.ThresholdID
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.ThresholdID = t2.ThresholdID
WHERE t1.Value < t2.threshold
SELECT * FROM Table1
JOIN Table2
ON table1.ThresholdID = table2.ThresholdID --(assuming table 2 holds the same value to link them together)
WHERE
value < thresholdvalue
A 'JOIN' connects 2 tables based on the 'ON' clause (which can be multipart, using 'AND' and 'OR')
If you have 3 entries in table 2 which share table1's primary key (a one-to-many association) you will receive 3 rows in your result set.
for the tables below, for example:
Table 1:
Key Value
1 Hi
2 Bye
Table 2:
Table1Key 2nd_word
1 You
1 fellow
1 friend
2 now
this query:
SELECT * FROM Table1
JOIN Table2
on table1.key = table2.table1key
gets this result set:
Key Value Table1Key 2nd_word
1 Hi 1 You
1 Hi 1 fellow
1 Hi 1 friend
2 Bye 2 now
Note that JOIN will only return results when there is a match in the 2nd table, it will not return a result if there is no match. You can LEFT JOIN for that (all fields from the second table will be NULL).
JOINs can also be strung together, the result from the previous JOIN is used in place of the original table.
Related
I am trying to find the "users" that are missing a value in a 2nd table with the value of column "A" = 16 and then column "B" = 0.
I am looking for these values because that would give me the ability to run a query adding a row for each user that is missing the row with the values of A = 16 and B = 0.
So here is the relevant structure of the tables that we would be joining on.
There are two tables, table 1 and table 2
Table 1
ID
parent id
table 2
table1_id
A
B
The problem I am running into is that table2 can have records associated with the table1_id but still needing to verify if the table2 if there is not a row with table1_id, A missing value 16 while B is missing value 0.
Here is the current idea I am working off of for the sql query
SELECT
*
FROM
table1
LEFT JOIN
table2 ON table1.id = table2.table1_id
WHERE
table1.id IS NOT NULL
AND table2.id IS NULL;
This will give me all the table1_ids that are missing records from table2 but does however would not pull the rows where there are rows for the table1_id but however does not determine if there are missing rows with the column A with value 16 or Column B = 0.
If you are able to answer that would be greatly appreciated. I just currently cannot think of a way I can logically create a query that would do this.
So, you want all rows from table 1
And you want rows from table 2 that are A=16, B=0
And you want to know where the relationship breaks down between table1 and table2:
SELECT t1.*
FROM
table1 t1
LEFT JOIN
(
SELECT * FROM table2 WHERE A=16 and B=0
) a16b0
ON
t1.id = a16b0.table1_id
WHERE
a16b0.table1_id IS NULL
There are more ways to skin this cat, but this should be fairly understandable in the sense of "join table1 to (just the a16/b0 rows from table2)"
Another form you might get on with uses EXISTS:
SELECT * FROM table1 t1
WHERE NOT EXISTS(
SELECT null FROM table2 t2
WHERE t2.table1_id = t1.id AND t2.A = 16 AND t2.B = 0
)
In english it's "Select all from table 1 where, for any particular t1 row, there does not exist a t2 row that has: a matching id in table1_id, a 16 in a, a 0 in b"
A slightly less popular form (historical performance reasons probably) would be perhaps:
SELECT * FROM table1 t1
WHERE id NOT IN (
SELECT table1_id FROM table2 WHERE A = 16 AND B = 0
)
"select everything from table1 where the row's id is not in the list of IDs that are a16/b0 from table 2" - in essence this forms a "big list of everything we dont want" and then says "get me everything that isn't in the list of don't-wants"
This is the solution.
SELECT
*
FROM
table1
LEFT JOIN
table1.id = table2.table1_id AND table2.A = 16 AND table2.B = 0
WHERE
table2.id IS NULL;
#jon Armstrong, thanks for the help.
I have two tables.
Table 1
Id
UpdateId
Name
Table 2
Table1ID
UpdateID
Address
Each time user update, system will insert record to table1. But for table2, system only insert record when there is update in address.
Sample data
Table 1
1,1,name1
1,2,name1
1,3,name1update
1,4,name1update
1,5,name1
1,6,name2
Table 2
1,1,address
1,4,addressupdate
I want to get the result as following
1,1,name1,address
1,2,name1,address
1,3,name1update,address
1,4,name1update,addressupdate
1,5,name1,addressupdate
1,6,name2,addressupdate
How to make use of join condition to achieve as above?
You can use a correlated subquery. Here is standard syntax, but it can be easily adapted to any database:
select t1.*,
(select t2.addressid
from table2 t2
where t2.table1id = t1.id and
t2.updateid <= t1.updateid
order by t2.updateid desc
fetch first 1 row only
) as addressid
from table1 t1;
you can use left join when you want to take all columns from left table t1 even though it doesn't match with the other table with column updateid on t2 table.
select t1.id,t1.updateid,t1.name,t2.address from table1 t1
left join table2 t2
on t2.updateid= t1.updateid
you can read more about joins here
Basically I have 2 tables 1 OR 2 which is showed in below image.
i want to joint these 2 tables but the value column should be reflect only once in first entry only.
I have basic knowledge about SQL but please guide how can i get the required output as per the criteria which mention above.
You can do this with a left join:
select t2.*, t1.value
from table2 t2 left join
table1 t1
on t1.code = t2.code and t2.type = 'A';
I have two tables,
in table1 I have 5 rows and
in table2 3 rows
table1:
#no---Name---value
1-----John---100
2-----Cooper-200
3-----Mil----300
4-----Key----200
5-----Van----300
Table 2:
#MemID-#no---FavID
19-----1-----2
21-----1-----3
22-----2-----5
Now expected result:
#no---name---value---MyFav
1-----John---100-----NULL
2-----Cooper-200-----1
3-----Mil----300-----1
4-----Key----200-----NULL
5-----Van----300-----NULL
1 indicates - My favorites
MyFav - new column ( alias)
This is the expected result, please suggest how to get it.
I think I understand the logic. You want MyFav to be marked as a 1 if that row is a favorite of John. You can do this with a left join and some more filtering:
select t1.*,
(case when t2.#no is not null then 1 end) as MyFav
from table1 t1 left join
table2 t2
on t1.#no = t2.FavId and
t2.#no = (select tt1.#no from table1 tt1 where tt1.Name = 'John');
Just use natural join for that, It will use your primary key as a mediator to join both the tables, as required. In your case, I think primary key is #no
For more information on natural join please visit SQL Joins
this is a simplified version of a problem I'm having,
I have two tables:
Table1 has two columns (Stuff, YesNo) and
Table2 has one column (Stuff)
The records in the YesNo Column will either be 1 or 0
How could I select records in Table2 where the records in Table1.YesNo = 1
Many Thanks
SELECT Table2.*
FROM Table2
INNER JOIN Table1 ON Table1.Stuff = Table2.Stuff
WHERE Table1.YesNo = 1
If I understand you correctly, this would be your solution:
Select Stuff From Table2
Where Exists (
Select 'Y'
From Table1
Where Table1.Stuff = Table2.Stuff
And YesNo = 1
)
As I believe you'll need data from both tables and you may want to render fields unique to each table This seems like a likely response. However, as I don't believe STUFF accurately represents the relationship... you'll need to quantify/adjust the on a.stuff = b.stuff so that the join includes all necessary fields.
SELECT A.Stuff, B.Stuff, B.YesNo
FROM table1 B
INNER JOIN table2 A
on A.Stuff = B.Stuff
WHERE B.YesNo = 1
SELECT T2.*
FROM TABLE1 T1
JOIN TABLE2 T2
ON T1.Stuff = T2.Stuff
WHERE T1.YesNo = 1