I am super new to SQL and have two queries I think should produce the same output but they don't. Can someone figure out the difference between them?
The input table for this simple example has two columns, letter and extra. The data in the first column is a random letter from the list ['a', 'b', 'c', 'd', 'e'] and extra should not matter (I think?). These are the queries:
update
tbl
set
extra = letter;
and:
update
tbl
set
extra = (select
letter
from tbl);
The resulting tables these produce are:
e|e
e|e
c|c
e|e
b|b
...
and:
e|e
e|e
c|e
e|e
b|e
...
respectively.
I expect the first output for both queries, how come the second one turns out as it does?
EDIT:
The reason I ask this question is because what I want to do is a bit more involved than this simple example and I believe I need the subquery. I am trying to add a kind of normalisation column, like this:
update
tbl
set
extra = 1 / (select
norm
from
tbl
INNER JOIN
(SELECT
letter, count(*) as norm
FROM
tbl
GROUP BY letter) as tmp
ON
tbl.letter = tmp.letter);
Alas, this obviously doesn't work because of the above.
What your first query is saying:
Set the value of extra to the value of letter in the same row.
What the second query is saying:
Pick a value from the column "letter" in the table, and update every row in the table to have the column 'extra' contain that value.
They are different instructions, so you get different results.
Related
I have an initial query written below and need to find values in the quote_id column that different but the corresponding values in the benefit_plan_cd column are the same. The output should look like the below. I know the prospect_nbr for this issue which is why I am able to add it to my initial query to get the expected results but need to be able to find other ones going forward.
select prospect_nbr, qb.quote_id, quote_type, effective_date,
benefit_plan_cd, package_item_cd
from qo_benefit_data qb
inner join
qo_quote qq on qb.quote_id = qq.quote_id
where quote_type = 'R'
and effective_date >= to_date('06/01/2022','mm/dd/yyyy')
and package_item_cd = 'MED'
Output should look like something like this excluding the other columns.
quote_id benefit_plan_cd
514 1234
513 1234
Let's do this in two steps.
First take your existing query and add the following at the end of your select list:
select ... /* the columns you have already */
, count(distinct quote_id partition by benefit_plan_id) as ct
That is the only change - don't change anything else. You may want to run this first, to see what it produces. (Looking at a few rows should suffice, you don't need to look at all the rows.)
Then use this as a subquery, to filter on this count being > 1:
select ... /* only the ORIGINAL columns, without the one we added */
from (
/* write the query from above here, as a SUBquery */
)
where ct > 1
;
Can I select a column based on another column's value being listed as a formula? So I have a table, something like:
column_name formula val
one NULL 1
two NULL 2
three one + two NULL
And I want to do
SELECT
column_name,
CASE WHEN formula IS NULL
val
ELSE
(Here's where I'm confused - How do I evaluate the formula?)
END as result
FROM
table
And end up with a result set like
column_name result
one 1
two 2
three 3
You keep saying column, and column name, but you're actually talking about rows, not columns.
The problem is that you (potentially) want different formulas for each row. For example, row 4 might be (two - one) = 1 or even (three + one) = 4, where you'd have to calculate row three before you could do row 4. This means that a simple select query that parses the formulas is going to be very hard to do, and it would have to be able to handle each type of formula, and even then if the formulas reference other formulas that only makes it harder.
If you have to be able to handle functions like (two + one) * five = 15 and two + one * five = 7, then you'd be basically re-implementing a full blown eval function. You might be better to return the SQL table to another language that has eval functions built in, or you could use something like SQL Eval.net if it has to be in SQL.
Either way, though, you've still got to change "two + one" to "2 + 1" before you can do the eval with it. Because these values are in other rows, you can't see those values in the row you're looking at. To get the value for "one" you have to do something like
Select val from table where column_name = 'one'
And even then if the val is null, that means it hasn't been calculated yet, and you have to come back and try again later.
If I had to do something like this, I would create a temporary table, and load the basic table into it. Then, I'd iterate over the rows with null values, trying to replace column names with the literal values. I'd run the eval over any formulas that had no symbols anymore, setting the val for those rows. If there were still rows with no val (ie they were waiting for another row to be done first), I'd go back and iterate again. At the end, you should have a val for every row, at which point it is a simple query to get your results.
Possible solution would be like this kind....but since you mentioned very few things so this works on your above condition, not sure for anything else.
GO
SELECT
t1.column_name,
CASE WHEN t1.formula IS NULL
t1.val
ELSE
(select sum(t2.val) from table as t2 where t2.formula is not null)
END as result
FROM
table as t1
GO
If this is not working feel free to discuss it further.
I have the following query that is part of a common table expression. I don't understand the function of the "Select -1" statement. It is obviously different than the "Select 1" that is used in "EXISTS" statements. Any ideas?
select days_old,
count(express_cd),
count(*),
case
when round(count(express_cd)*100.0/count(*),2) < 1 then '0'
else ''
end ||
cast(decimal(round(count(express_cd)*100.0/count(*),2),5,2) as varchar(7)) ||
'%'
from foo.bar
group by days_old
union all
select -1, -- Selecting the -1 here
count(express_cd),
count(*),
case
when round(count(express_cd)*100.0/count(*),2) < 1 then '0'
else ''
end ||
cast(decimal(round(count(express_cd)*100.0/count(*),2),5,2) as varchar(7)) ||
'%'
from foo.bar
where days_old between 1 and 7
It's just selecting the number "minus one" for each row returned, just like "select 1" will select the number "one" for each row returned.
There is nothing special about the "select 1" syntax uses in EXISTS statements by the way; it's just selecting some random value because EXISTS requires a record to be returned and a record needs data; the number 1 is sufficient.
Why you would do this, I have no idea.
When you have a union statement, each part of the union must contain the same columns. From what I read when I look at this, the first statement is giving you one line for each days old value and then some stats for each day old. The second part of the union is giving you a summary of all the records that are only a week or so less. Since days old column is not relevant here, they put in a fake value as a placeholder in order to do the union. OF course this is just a guess based on reading thousands of queries through the years. To be sure, I would need to actually run teh code.
Since you say this is a CTE, to really understand why this is is happening, you may need to look at the data it generates and how that data is used in the next query that uses the CTE. That might answer your question.
What you have asked is basically about a business rule unique to your company. The true answer should lie in any requirements documents for the original creation of the code. You should go look for them and read them. We can make guesses based on our own experience but only people in your company can answer the why question here.
If you can't find the documentation, then you need to talk (Yes directly talk, preferably in person) to the Stakeholders who use the data and find out what their needs were. Only do this after running the code and analyzing the results to better understand the meaning of the data returned.
Based on your query, all the records with days_old between 1 and 7 will be output as '-1', that is what select -1 does, nothing special here and there is no difference between select -1 and select 1 in exists, both will output the records as either 1 or -1, they are doing the same thing to check whether if there has any data.
Back to your query, I noticed that you have a union all and compare each four columns you select connected by union all, I am guessing your task is to get a final result with days_old not between 1 and 7 and combine the result with day_old, which is one because you take all between 1 and 7.
It is just a grouping logic there.
Your query returns aggregated
data (counts and rounds) grouped by days_old column plus one more group for data where days_old between 1 and 7.
So, -1 is just another additional group there, it cannot be 1 because days_old=1 is an another valid group.
result will be like this:
row1: days_old=1 count(*)=2 ...
row2: days_old=3 count(*)=5 ...
row3: days_old=9 count(*)=6 ...
row4: days_old=-1 count(*)=7
I read many threads but didn't get the right solution to my problem. It's comparable to this Thread
I have a query, which gathers data and writes it per shell script into a csv file:
SELECT
'"Dose History ID"' = d.dhs_id,
'"TxFieldPoint ID"' = tp.tfp_id,
'"TxFieldPointHistory ID"' = tph.tph_id,
...
FROM txfield t
LEFT JOIN txfielpoint tp ON t.fld_id = tp.fld_id
LEFT JOIN txfieldpoint_hst tph ON fh.fhs_id = tph.fhs_id
...
WHERE d.dhs_id NOT IN ('1000', '10000')
AND ...
ORDER BY d.datetime,...;
This is based on an very big database with lots of tables and machine values. I picked my columns of interest and linked them by their built-in table IDs. Now I have to reduce my result where I get many rows with same values and just the IDs are changed. I just need one(first) row of "tph.tph_id" with the mechanics like
WHERE "Rownumber" is 1
or something like this. So far i couldn't implement a proper subquery or use the ROW_NUMBER() SQL function. Your help would be very appreciated. The Result looks like this and, based on the last ID, I just need one row for every og this numbers (all IDs are not strictly consecutive).
A01";261511;2843119;714255;3634457;
A01";261511;2843113;714256;3634457;
A01";261511;2843113;714257;3634457;
A02";261512;2843120;714258;3634464;
A02";261512;2843114;714259;3634464;
....
I think "GROUP BY" may suit your needs.
You can group rows with the same values for a set of columns into a single row
I'm working with a database, where one of the fields I extract is something like:
1-117 3-134 3-133
Each of these number sets represents a different set of data in another table. Taking 1-117 as an example, 1 = equipment ID, and 117 = equipment settings.
I have another table from which I need to extract data based on the previous field. It has two columns that split equipment ID and settings. Essentially, I need a way to go from the queried column 1-117 and run a query to extract data from another table where 1 and 117 are two separate corresponding columns.
So, is there anyway to split this number to run this query?
Also, how would I split those three numbers (1-117 3-134 3-133) into three different query sets?
The tricky part here is that this column can have any number of sets here (such as 1-117 3-133 or 1-117 3-134 3-133 2-131).
I'm creating these queries in a stored procedure as part of a larger document to display the extracted data.
Thanks for any help.
Since you didn't provide the DB vendor, here's two posts that answer this question for SQL Server and Oracle respectively...
T-SQL: Opposite to string concatenation - how to split string into multiple records
Splitting comma separated string in a PL/SQL stored proc
And if you're using some other DBMS, go search for "splitting text ". I can almost guarantee you're not the first one to ask, and there's answers for every DBMS flavor out there.
As you said the format is constant though, you could also do something simpler using a SUBSTRING function.
EDIT in response to OP comment...
Since you're using SQL Server, and you said that these values are always in a consistent format, you can do something as simple as using SUBSTRING to get each part of the value and assign them to T-SQL variables, where you can then use them to do whatever you want, like using them in the predicate of a query.
Assuming that what you said is true about the format always being #-### (exactly 1 digit, a dash, and 3 digits) this is fairly easy.
WITH EquipmentSettings AS (
SELECT
S.*,
Convert(int, Substring(S.AwfulMultivalue, V.Value * 6 - 5, 1) EquipmentID,
Convert(int, Substring(S.AwfulMultivalue, V.Value * 6 - 3, 3) Settings
FROM
SourceTable S
INNER JOIN master.dbo.spt_values V
ON V.Value BETWEEN 1 AND Len(S.AwfulMultivalue) / 6
WHERE
V.type = 'P'
)
SELECT
E.Whatever,
D.Whatever
FROM
EquipmentSettings E
INNER JOIN DestinationTable D
ON E.EquipmentID = D.EquipmentID
AND E.Settings = D.Settings
In SQL Server 2005+ this query will support 1365 values in the string.
If the length of the digits can vary, then it's a little harder. Let me know.
Incase if the sets does not increase by more than 4 then you can use Parsename to retrieve the result
Declare #Num varchar(20)
Set #Num='1-117 3-134 3-133'
select parsename(replace (#Num,' ','.'),3)
Result :- 1-117
Now again use parsename on the same resultset
Select parsename(replace(parsename(replace (#Num,' ','.'),3),'-','.'),1)
Result :- 117
If the there are more than 4 values then use split functions