I need to return elements from a database query based on an inequality using the lexicographic ordering on multiple columns. As described in this question this is straightforward if I'm comparing all the columns in the same direction. Is there a straigtforward way to do this if I want to reverse the direction of the sort on some columns.
For instance, I might have columns A, B and C and values 5, 7, and 23 and I'd like to return something like:
WHERE A < 5 OR (A = 5 AND B > 7) OR (A = 5 AND B = 7 AND C < 23)
Is there any easier way to do this using tuples (I have to construct in a function without knowing the number of columns beforehand)? Note that, some columns are DateTime columns so I can't rely on tricks that apply only to integers (e.g. negating both sides). I'm happy to use postgresql specific tricks.
And, if not, is there a specific way/order I should build expressions like the above to best use multicolumn indexes?
Just thinking if going the CTE route and creating a column which stores 0 or 1 for whether the data passes the specific filter criteria or not.
WITH CTE AS
(
SELECT
..,
...,
CASE
WHEN A < 5 THEN 1
WHEN A = 5 AND B > 7 THEN 1
WHEN A = 5 AND B = 7 AND C < 23 THEN 1
ELSE 0
END AS filter_criteria
)
SELECT
..,
..
FROM
CTE
WHERE filter_criteria = 1
OR, directly applying the CASE statement in the WHERE clause. This reduces the extra step of CTE
WHERE 1 = CASE
WHEN A < 5 THEN 1
WHEN A = 5 AND B > 7 THEN 1
WHEN A = 5 AND B = 7 AND C < 23 THEN 1
ELSE 0
END
Referring to the thread you mentioned, can you try the idea WHERE (col_a, 'value_b') > ('value_a', col_b)
Related
I'm using Postgresql as my database, in case that's helpful, although I'd like to find a pure SQL approach instead of a Postgresql specific implementation.
I have a large set of test data obtained from manufacturing a piece of electronics and I'd like to take that set of data and extract from it which units met certain criteria during test, ideally using a separate table that contains the test criteria from each step of manufacturing.
As a simple example, let's say I check the temperature readback from the unit in two different steps of the test. In step 1, the temperature should be in the range of 20C-30C while step 2 should be in the range of 50C-60C.
Let's assume the following table structure with a set of example data (table name 'test_data'):
temperature step serial_number
25 1 1
55 2 1
19 1 2
20 2 2
and let's assume the following table that contains the above mentioned pass criteria (table name 'criteria'):
temperature_upper temperature_lower step
20 30 1
50 60 2
At the moment, using a static approach, I can just use the following query:
SELECT * FROM test_data WHERE
( test_data.step = 1 AND test_data.temperature > 20 AND test_data.temperature < 30 ) OR
( test_data.step = 2 AND test_data.temperature > 50 AND test_data.temperature < 60 );
which would effectively yield the following table:
temperature step serial_number
25 1 1
55 2 1
I'd like to make my select query more dynamic and instead of begin statically defined, make it construct itself off of a list of results from the test_criteria table. The hope is to grow this into a complex query where temperature, voltage and current might be checked in step 1 but only current in step 2, for example.
Thanks for any insight!
You can solve using a join between the tables
SELECT t.*
FROM test_data t
INNER JOIN criteria c ON t.step = c.step
AND t.temperature > c.temperature_upper
AND t.temperature < c.temperature_lower
OR if you want >= and <=
SELECT t.*
FROM test_data t
INNER JOIN criteria c ON t.step = c.step
AND t.temperature netween c.temperature_upper AND c.temperature_lower
I have 2 tables I am combining and that works but I think I designed the second table wrong as I have a column for each item of what really is a multiple choice question. The query is this:
select Count(n.ID) as MemCount, u.Pay1Click, u.PayMailCC, u.PayMailCheck, u.PayPhoneACH, u.PayPhoneCC, u.PayWuFoo
from name as n inner join
UD_Demo_ORG as u on n.ID = u.ID
where n.MEMBER_TYPE like 'ORG_%' and n.CATEGORY not like '%_2' and
(u.Pay1Click = '1' or u.PayMailCC = '1' or u.PayMailCheck = '1' or u.PayPhoneACH = '1' or u.PayPhoneCC = '1' or u.PayWuFoo = '1')
group by u.Pay1Click, u.PayMailCC, u.PayMailCheck, u.PayPhoneACH, u.PayPhoneCC, u.PayWuFoo
The results come up like this:
Count Pay1Click PayMailCC PayMailCheck PayPhoneACH PayPhoneCC PayWuFoo
8 0 0 0 0 0 1
25 0 0 0 0 1 0
8 0 0 0 1 0 0
99 0 0 1 0 0 0
11 0 1 0 0 0 0
So the question is, how can I get this to 2 columns, Count and then the headers of the next 6 headers so the results look like this:
Count PaymentType
8 PayWuFoo
25 PayPhoneCC
8 PayPhoneACH
99 PayMailCheck
11 PayMailCC
Thanks.
Try this one
Select Count,
CASE WHEN Pay1Click=1 THEN 'Pay1Click'
PayMailCC=1 THEN ' PayMailCC'
PayMailCheck=1 THEN 'PayMailCheck'
PayPhoneACH=1 THEN 'PayPhoneACH'
PayPhoneCC=1 THEN 'PayPhoneCC'
PayWuFoo=1 THEN 'PayWuFoo'
END as PaymentType
FROM ......
I think indeed you made a mistake in the structure of the second table. Instead of creating a row for each multiple choice question, i would suggest transforming all those columns to a 'answer' column, so you would have the actual name of the alternative as the record in that column.
But for this, you have to change the structure of your tables, and change the way the table is populated. you should get the name of the alternative checked and put it into your table.
More on this, you could care for repetitive data in your table, so writing over and over again the same string could make your table grow larger.
if there are other things implied to the answer, other informations in the UD_Demo_ORG table, then you can normalize the table, creating a payment_dimension table or something like this, give your alternatives an ID such as
ID PaymentType OtherInfo(description, etc)...
1 PayWuFoo ...
2 PayPhoneCC ...
3 PayPhoneACH ...
4 PayMailCheck ...
5 PayMailCC ...
This is called a dimension table, and then in your records, you would have the ID of the payment type, and not the information you don't need.
So instead of a big result set, maybe you could simplify by much your query and have just
Count PaymentId
8 1
25 2
8 3
99 4
11 5
as a result set. it would make the query faster too, and if you need other information, you can then join the table and get it.
BUT if the only field you would have is the name, perhaps you could use the paymentType as the "id" in this case... just consider it. It is scalable if you separate to a dimension table.
Some references for further reading:
http://beginnersbook.com/2015/05/normalization-in-dbms/ "Normalization in DBMS"
http://searchdatamanagement.techtarget.com/answer/What-are-the-differences-between-fact-tables-and-dimension-tables-in-star-schemas "Differences between fact tables and dimensions tables"
I am refactoring some old oracle sql statements containing plenty of conditions. Some are single conditions put into brackets. Now, does the brackets matter for single conditions? Is there a difference between the two examples below?
example 1
WHERE
(
A = B
AND B = C
)
AND ( A > 5 )
AND ( B <> 0 )
example 2
WHERE
(
A = B
AND B = C
)
AND A > 5
AND B <> 0
As far as I know there ain't any semantic differences.
In my experience usually this is either
a relic of some old condition (maybe an OR was in that bracket somewhere in the past) or
just the style of the dev working in this.
There is no difference between the two examples you have posted. Oracle query executes from the end i.e your where condition's last part is filtered first and runs back eg:- where first filter condition would be b<>0 then A>5 ,so on.
Its good practice to use brackets when using AND and OR operators together as without brackets soemtimes the logic is unclear ,otherwise with only AND operator bracket doesn't make any difference
What about logic: you do need brackets if you have some OR logic, but in this case (only AND) it has no meaning. You can remove all brackets in your query.
And if we'll go deep: look the explain query analyze, you can see that interpreter puts brackets automatically even you missed it.
All are same until you have only AND. But if you have any other operator then comes the question of precedence.
example 1
WHERE
(
A = B
AND B = C
)
AND ( A > 5 )
AND ( B <> 0 )
example 2
WHERE
(
A = B
AND B = C
)
AND A > 5
AND B <> 0
example 3
WHERE
A = B
AND B = C
AND A > 5
AND B <> 0
I am a long time fan of Stack Overflow but I've come across a problem that I haven't found addressed yet and need some expert help.
I have a query that is sorted chronologically with a date-time compound key (unique, never deleted) and several pieces of data. What I want to know is if there is a way to find the start (or end) of a region where a value changes? I.E.
DateTime someVal1 someVal2 someVal3 target
1 3 4 A
1 2 4 A
1 3 4 A
1 2 4 B
1 2 5 B
1 2 5 A
and my query returns rows 1, 4 and 6. It finds the change in col 5 from A to B and then from B back to A? I have tried the find duplicates method and using min and max in the totals property however it gives me the first and last overall instead of the local max and min? Any similar problems?
I didn't see any purpose for the someVal1, someVal2, and someVal3 fields, so I left them out. I used an autonumber as the primary key instead of your date/time field; but this approach should also work with your date/time primary key. This is the data in my version of your table.
pkey_field target
1 A
2 A
3 A
4 B
5 B
6 A
I used a correlated subquery to find the previous pkey_field value for each row.
SELECT
m.pkey_field,
m.target,
(SELECT Max(pkey_field)
FROM YourTable
WHERE pkey_field < m.pkey_field)
AS prev_pkey_field
FROM YourTable AS m;
Then put that in a subquery which I joined to another copy of the base table.
SELECT
sub.pkey_field,
sub.target,
sub.prev_pkey_field,
prev.target AS prev_target
FROM
(SELECT
m.pkey_field,
m.target,
(SELECT Max(pkey_field)
FROM YourTable
WHERE pkey_field < m.pkey_field)
AS prev_pkey_field
FROM YourTable AS m) AS sub
LEFT JOIN YourTable AS prev
ON sub.prev_pkey_field = prev.pkey_field
WHERE
sub.prev_pkey_field Is Null
OR prev.target <> sub.target;
This is the output from that final query.
pkey_field target prev_pkey_field prev_target
1 A
4 B 3 A
6 A 5 B
Here is a first attempt,
SELECT t1.Row, t1.target
FROM t1 WHERE (((t1.target)<>NZ((SELECT TOP 1 t2.target FROM t1 AS t2 WHERE t2.DateTimeId<t1.DateTimeId ORDER BY t2.DateTimeId DESC),"X")));
How can I select every thrid row from the table?
if a table has
1
2
3
4
5
6
7
8
9
records
it should pick up 3, 6,9 record. regards less what their data is.
Modulo is what you want...
Assuming contiguous values:
SELECT *
FROM Mytable
WHERE [TheColumn] Mod 3 = 0
And with gaps
SELECT *
FROM Mytable
WHERE DCount("TheColumn", "table", "TheColumn <= " & [TheColumn]) Mod 3 = 0
Edit: To exclude every 3rd record, ...Mod 3 <> 0
If its SQL you could use the row_number and over commands. see this, then where rownumvar % 3 =0 but not sure if that works in access.
Or you could put the table into a recordset and iterate through checking the index for % 3=0 if your using any kind of code.
How about a Count() on a field that has unique members. (id?) then % 3 on that.