A simplified example:
I have a SQL table called things. Things by themselves have an id and a name. Things are part of a tree, e.g. a thing can have a parent; Exactly how to this is stored is not important, important is however that it is possible to obtain a list of thing ids from the root node to the current thing.
I have another table, called properties. A property has a thing_id column, a name column and a value column.
I now want, for the current thing, to obtain all properties, ordered by thing_id, in order of the paths from root thing to current thing.
e.g., if the current thing is nested like this: Root(1) > Vehicle(4) > Car(2) > Hybrid(3), I would want the list of properties be returned with the properties that have a thing_id==1 first, followed by the ones with thing_id == 4, then thing_id==2 and finally thing_id==3.
How can this be done using SQL? (without using N+1 selects)
In SQL this can be achieved with use of recursive query. Here is an example
DECLARE #item as varchar(10)
with CTE (main_part, sub_part, NestingLevel)
as
(
select main_part, sub_part, 1 from tblParts
where main_part = #item
union all
select tblParts.main_part, tblParts.sub_part, (NestingLevel + 1) from tblParts
inner join CTE on tblParts.main_part = CTE.sub_part
)
select * from CTE
In order to address this in MySQL you can try temporary table approach. Here is a good example of it: How to do the Recursive SELECT query in MySQL?
Related
I want to find multiple rows where a JSON array contains a specific value or values. Sometimes all match items will need to match (ANDs), sometimes only some (ORs) and sometimes a combination of both (ANDs and ORs).
This is in Microsoft SQL Server 2017.
I've tried doing an AS statement in the select but that resulted in the alias created for the subquery not being recognised later on in the subquery.
The bellow example works, it just seems innificent and has code duplication.
How would I only specify SELECT VALUE FROM OPENJSON(JsonData, '$.categories' once? Or perhaps there is some other way to do this?
DECLARE #TestTable TABLE
(
Id int,
JsonData nvarchar(4000)
);
INSERT INTO #TestTable
VALUES
(1,'{"categories":["one","two"]}'),
(2,'{"categories":["one"]}'),
(3,'{"categories":["two"]}'),
(4,'{"categories":["one","two","three"]}');
SELECT [Id]
FROM #TestTable
WHERE ISJSON(JsonData) = 1
-- These two lines are the offending parts of code
AND 'one' in (SELECT VALUE FROM OPENJSON(JsonData, '$.categories'))
AND 'two' in (SELECT VALUE FROM OPENJSON(JsonData, '$.categories'));
The table format cannot change, though I can add computed columns - if need be.
Well, I'm not sure if this helps you...
It might help to transform the nested array to a derived table to use it as a CTE. Check this out:
DECLARE #TestTable TABLE
(
Id int,
JsonData nvarchar(4000)
);
INSERT INTO #TestTable
VALUES
(1,'{"categories":["one","two"]}'),
(2,'{"categories":["one"]}'),
(3,'{"categories":["two"]}'),
(4,'{"categories":["one","two","three"]}');
--This is the query
WITH JsonAsTable AS
(
SELECT Id
,JsonData
,cat.*
FROM #TestTable tt
CROSS APPLY OPENJSON(tt.JsonData,'$.categories') cat
)
SELECT *
FROM JsonAsTable
The approach is very close to the query you formed yourself. The result is a table with one line per array entry. The forme Id is a repeated grouping key, the key is the ordinal position within the array, while the value is one of the words you are searching for.
In your query you can use JsonAsTable like you'd use any other table in this place.
But - instead of the repeated FROM OPENJSON queries - you will need repeated EXISTS() predicates...
A hacky solution might be this:
SELECT Id
,JsonData
,REPLACE(REPLACE(REPLACE(JsonData,'{"categories":[','",'),']}',',"'),'","',',')
FROM #TestTable
This will return all nested array values in one string, separated by a comma. You can query this using a LIKE pattern... You could return this as computed column though...
I have a string for example 'p2p3p4p9c5c6c7' I want to make a select-statement in mysql that returns how much of those strings ('p6','p7','p8' or 'p9') are containing in the initial string.
The result of my example should be 1, because only 'p9' is containing in my string.
I don't find a good way to do that. Can someone help?
another example
'k2p4p6p8p9c8' the result should be here 3
You would seem to have a poor data format. If you want to store lists of things, use a junction table.
However, the best answer that I can think of is a set of conditions that are added together:
select ((str like '%p6%') +
(str like '%p7%') +
(str like '%p8%') +
(str like '%p9%')
) as NumInString
MySQL treats booleans as integers in a numeric context, with "1" for true and "0" for false.
I should repeat that if the substrings are really codes of some type, then these should be stored in a separate junction table, with one row per code and original row.
SELECT count(*) FROM
(SELECT 'p2p3p4p9c5c6c7' AS a) AS string_table
INNER JOIN
(SELECT 'p6' AS b UNION ALL
SELECT 'p7' UNION ALL
SELECT 'p8' UNION ALL
SELECT 'p9') AS list_table
ON INSTR(string_table.a,list_table.b) > 0;
I cannot create a virtual table for this. Basically what I have, is a list of values:
'Succinylcholine','Thiamine','Trandate','Tridol Drip'
I want to know which of those values is not present in table1 and display them. Is this possible? I have tried using left joins and creating a variable with the list which I can compare to the table, but it returns the wrong results.
This is one of the things I have tried:
SET #list="'Amiodarone','Ammonia Inhalents','Aspirin';
SELECT #list FROM table1 where #list not in (
SELECT Description
FROM table1
);
With only narrow exceptions, you need to have data in table form to be able to obtain those data in your result set. This is the essential problem that all attempts at a solution to this problem run into, given that you cannot create a temporary table. If indeed you can provide the input in any form or format (per your comment), then you can provide it in the form of a subquery:
(
SELECT 'Amiodarone' AS description
UNION ALL
SELECT 'Ammonia Inhalents'
UNION ALL
SELECT 'Aspirin'
)
(Note that that exercises the biggest of the exceptions I noted: you can select scalars directly, without a base table. If you like, you can express that explicitly -- in MySQL and Oracle, at least -- by selecting FROM DUAL.)
In that case, this should work for you:
SELECT
a.description
FROM
(
SELECT 'Amiodarone' AS description
UNION ALL
SELECT 'Ammonia Inhalents'
UNION ALL
SELECT 'Aspirin'
) a
LEFT JOIN table1
ON a.description = table1.description
WHERE table1.description IS NULL
That won't work. the variable's contents will be treated as a monolithic string - one solid block of letters, not 3 separate comma-separated values. The query will be parsed/executed as:
SELECT ... WHERE "'Amio.....rin'" IN (x,y,z,...)
^--------------^--- string
Plus, since you're just doing a sub-select on the very same table, there's no point in this kind of a construct. You could try mysql find_in_set() function:
SELECT #list
FROM table1
WHERE FIND_IN_SET(Description, #list) <> ''
i'm preparing a presentation about one of our apps and was asking myself the following question: "based on the data stored in our database, how much growth have happend over the last couple of years?"
so i'd like to basically show in one output/graph, how much data we're storing since beginning of the project.
my current query looks like this:
SELECT DATE_FORMAT(created,'%y-%m') AS label, COUNT(id) FROM table GROUP BY label ORDER BY label;
the example output would be:
11-03: 5
11-04: 200
11-05: 300
unfortunately, this query is missing the accumulation. i would like to receive the following result:
11-03: 5
11-04: 205 (200 + 5)
11-05: 505 (200 + 5 + 300)
is there any way to solve this problem in mysql without the need of having to call the query in a php-loop?
Yes, there's a way to do that. One approach uses MySQL user-defined variables (and behavior that is not guaranteed)
SELECT s.label
, s.cnt
, #tot := #tot + s.cnt AS running_subtotal
FROM ( SELECT DATE_FORMAT(t.created,'%y-%m') AS `label`
, COUNT(t.id) AS cnt
FROM articles t
GROUP BY `label`
ORDER BY `label`
) s
CROSS
JOIN ( SELECT #tot := 0 ) i
Let's unpack that a bit.
The inline view aliased as s returns the same resultset as your original query.
The inline view aliased as i returns a single row. We don't really care what it returns (except that we need it to return exactly one row because of the JOIN operation); what we care about is the side effect, a value of zero gets assigned to the #tot user variable.
Since MySQL materializes the inline view as a derived table, before the outer query runs, that variable gets initialized before the outer query runs.
For each row processed by the outer query, the value of cnt is added to #tot.
The return of s.cnt in the SELECT list is entirely optional, it's just there as a demonstration.
N.B. The MySQL reference manual specifically states that this behavior of user-defined variables is not guaranteed.
So my query is the following, which may return many results:
SELECT P_CODE, NAME FROM TEST.dbo.PEOPLE
WHERE NAME LIKE '%JA%'
AND P_CODE LIKE '%003%'
AND DOB LIKE '%1958%'
AND HKID = ''
AND (MOBILE LIKE '%28%' OR TEL LIKE '%28%')
I would like to integrate this into a Stored Procedure (or View?) so that it will only return a result if the query results in exactly 1 row. If there's 0 or > 1, then it should return no results.
If you just want to return an empty resultset in cases other than 1:
;WITH x AS
(
SELECT P_CODE, NAME, c = COUNT(*) OVER()
FROM TEST.dbo.PEOPLE
WHERE NAME LIKE '%JA%'
AND P_CODE LIKE '%003%'
AND DOB LIKE '%1958%'
AND HKID = ''
AND (MOBILE LIKE '%28%' OR TEL LIKE '%28%')
)
SELECT P_CODE, NAME FROM x WHERE c = 1;
Otherwise, you'll have to run the query twice (or dump the results to intermediate storage, such as a #temp table) - once to get the count, and once to decide based on the count whether to run the SELECT or not.
Effectively you want something akin to FirstOrDefault() from the Linq-to-SQL implementation but done on the server-side which means you will need to execute the query in a stored procedure, dumping the results into a temp table variable and then access ##ROWCOUNT afterwards to get the number of rows that were returned and then decide whether or not to forward the results on to the caller. If you do, be sure to use TOP 1 in the query from the temp table so that you only get a single result out as you desire.
UPDATE:
I described the alternate solution from what Aaron describes in his answer (which I like better).
Removed unnecessary TOP specifier in solution specification.