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.
Related
I have a table like this one (in a SQL SERVER):
field_name
field_descriptor
tag1
tag2
tag3
tag4
tag5
house
your home
home
house
null
null
null
car
first car
car
wheel
null
null
null
...
...
...
...
...
...
...
I'm developing a WIKI with a searchbar, which should be able to handle a query with more than one string for search. As an user enters a second string (spaced) the query should be able to return results that match restrictively the two strings (if exists) in any column, and so with a three string search.
Easy to do for one string with a simple SELECT with ORs.
Tried in the fronted in JS with libraries like match-sorter but it's heavy with a table with more than 100,000 results and more in the future.
I thought the query should do the heavy work, but maybe there is no simple way doing it.
Thanks in advance!
Tried to do the heavy work with all results in frontend with filtering and other libraries like match-sorter. Works but take several seconds and blocks the front.
Tried to create a simple OR/AND query but the posibilities with 3 search-strings (could be 1, 2 or 3) matching any column to any other possibility is overwhelming.
You can use STRING_SPLIT to get a separate row per search word from the search words string. Then only select rows where all search words have a match.
The query should look like this:
select *
from mytable t
where exists
(
select null
from (select value from string_split(#search, ' ')) search
having min(case when search.value in (t.tag1, t.tag2, t.tag3, t.tag4, t.tag5) then 1 else 0 end) = 1
);
Unfortunately, SQL Server seems to have a flaw (or even a bug) here and reports:
Msg 8124 Level 16 State 1 Line 8
Multiple columns are specified in an aggregated expression containing an outer reference. If an expression being aggregated contains an outer reference, then that outer reference must be the only column referenced in the expression.
Demo: https://dbfiddle.uk/kNL1PVOZ
I don't have more time at hand right now, so you may use this query as a starting point to get the final query.
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.
What does this query try to achieve?
SELECT * FROM X WHERE (X.Y in (select Y from X))
As far as I figured, it is yielding me the same result as
SELECT * FROM X WHERE Y is not NULL
Is there anything more to the first query? The first query is actually very slow with a large dataset and hence I want to know whether I can replace it with the second query.
You are right, the two queries are equivalent.
It is unclear, why the first query was written this way. Maybe it looked different once.
As is, your second query is better, because it is easier to read and understand (and even faster as you say).
your second query is perfect than the 1st one
because in 1st query you may get abnormal(null) result in case if column Y contains null value but you will not get abnormal result in 2nd one if null values contain in column Y.
So based on values of your table two query will behave two different way
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
A little background:
I have two tables imported from excel. One is 300k + rows so when I do updates to it in excel it just runs too slow, and often doesn't process on my comp. Anyways, I used a 'outer' left join to bring the two together.
Now when I run the query, I get the result which works fine but I need to add some fields to these results.
I am hoping to mimic what Ive done in excel, so I can create my summary pivots in the same manner.
First, I need a field that just concatenates two others after the join.
Then I need to add a field the equivalent of:
1/Countif($T$2:$T$3330,T2) from excel to access. However, the range does not need to be fixed. I will get it so that all the text entries are at the top of the field, so in theory, i need the equivalent of Sheets("").Range("T2").End(xldown). This proportion is used to eliminate double counting when i do pivot tables.
I am probably making this much more complicated than it has to be but I am new to Access as well, so please try to explain some things in explanations.
Thanks
Edit: I currently have:
Select [Table1].*, [Table2].PlaySk, [Table2].Service
From [Table1] Left Join [Table2] On [Table1].Play + [Table1].Skill
= [Table2].PlaySk
And in a general case, what I am trying to solve is something to get ColAB and ColProportion.
ColA ColB ColAB ColProportion
a 1 a1 .5
b 1 b1 1
a 1 a1 .5
b 2 b2 .3333333
b 2 b2 .3333333
b 2 b2 .3333333
Sounds to me like you'll need to make a couple queries in sequence to do everything you need.
The first part (concatenate) is relatively easy though -- just take the two field names you wish to concatenate together, say [Play] and [Skill], and, in design view, make a new field like "PlaySk: [Play] & [Skill]".
If you want to put a character between them (I often do when I concatenate, just to keep things straight), like a semicolon for example, you can do "PlaySk: [Play] & ';' & [Skill]".
As for the second part, I think you'll want to build a "Group By" query on top of the other one. In your original query, make another field in design view like this: "T2_Counter: Iif([The field you're checking, i.e. whatever column T is] = 'whatever value you're checking for, i.e. whatever T2 is',1,0)". This will result in a column that's a 1 when the check is true, and a zero otherwise.
Then bring this query into a new one, click "Totals" at the top in the Design tab, then bring the fields you want to group by down. Then create a field in design view like this: "MagicField: 1/Sum(T2_Counter)".
Hopefully this helps get you started at least.