I'm performing an Sqlite3 query similar to
SELECT * FROM nodes WHERE name IN ('name1', 'name2', 'name3', ...) LIMIT 1
Am I guaranteed that it will search for name1 first, name2 second, etc? Such that by limiting my output to 1 I know that I found the first hit according to my ordering of items in the IN clause?
Update: with some testing it seems to always return the first hit in the index regardless of the IN order. It's using the order of the index on name. Is there some way to enforce the search order?
The order of the returned rows is not guaranteed to match the order of the items inside the parenthesis after IN.
What you can do is use ORDER BY in your statement with the use of the function INSTR():
SELECT * FROM nodes
WHERE name IN ('name1', 'name2', 'name3')
ORDER BY INSTR(',name1,name2,name3,', ',' || name || ',')
LIMIT 1
This code uses the same list from the IN clause as a string, where the items are in the same order, concatenated and separated by commas, assuming that the items do not contain commas.
This way the results are ordered by their position in the list and then LIMIT 1 will return the 1st of them which is closer to the start of the list.
Another way to achieve the same results is by using a CTE which returns the list along with an Id which serves as the desired ordering of the results, which will be joined to the table:
WITH list(id, item) AS (
SELECT 1, 'name1' UNION ALL
SELECT 2, 'name2' UNION ALL
SELECT 3, 'name3'
)
SELECT n.*
FROM nodes n INNER JOIN list l
ON l.item = n.name
ORDER BY l.id
LIMIT 1
Or:
WITH list(id, item) AS (
SELECT * FROM (VALUES
(1, 'name1'), (2, 'name2'), (3, 'name3')
)
)
SELECT n.*
FROM nodes n INNER JOIN list l
ON l.item = n.name
ORDER BY l.id
LIMIT 1
This way you don't have to repeat the list twice.
Related
select m.value
from MY_TABLE m
where m.value in (select m2.some_third_value, m2.some_fourth_value
from MY_TABLE_2 m2
where m2.first_val member of v_my_array
or m2.second_val member of v_my_array_2)
Is it possible to write a select similar to this, where m.value is compared to two columns and has to match at least one of those? Something like where m.value in (select m2.first_val, m2.second_val). Or is writing two separate selects unavoidable here?
No. When there are multiple columns in the IN clause, there must be the same number of columns in the WHERE clause. The pairwise query compares each record in the WHERE clause against the records returned by the sub-query. The statement below
SELECT *
FROM table_main m
WHERE ( m.col_1, m.col_2 ) IN (SELECT s.col_a,
s.col_b
FROM table_sub s)
is equivalent to
SELECT *
FROM table_main m
WHERE EXISTS (SELECT 1
FROM table_sub s
WHERE m.col_1 = s.col_a
AND m.col_2 = s.col_b)
The only way to search both columns in one SELECT statement would be to OUTER JOIN the second table to the first table.
SELECT m.*
FROM table_main m
LEFT JOIN table_sub s ON (m.col_1 = s.col_a OR m.col_1 = s.col_b)
WHERE m.col_1 = s.col_a
OR m.col_1 = s.col_b
I'm trying to update a table with to many rows 388.000.
This is the query:
update DL_RG_ANALYTICS.SH_historico
from
(
SELECT
CAST((MAX_DIA - DIA_PAGO) AS INTEGER) AS DIAS_AL_CIERRE_1
FROM
(SELECT * FROM DL_RG_ANALYTICS.SH_historico A
LEFT JOIN
(SELECT ANO||MES AS ANO_MES, MAX(DIA) AS MAX_DIA FROM DL_RG_ANALYTICS.SH_CALENDARIO
GROUP BY 1) B
ON A.ANOMES = B.ANO_MES
) M) N
SET DIAS_AL_CIERRE = DIAS_AL_CIERRE_1;
Any help is apreciate.
This first thing I'd do is replace the SELECT * with only the columns you need. You can also remove the M derived table to make it easier to read:
UPDATE DL_RG_ANALYTICS.SH_historico
FROM (
SELECT CAST((MAX_DIA - DIA_PAGO) AS INTEGER) AS DIAS_AL_CIERRE_1
FROM DL_RG_ANALYTICS.SH_historico A
LEFT JOIN (
SELECT ANO || MES AS ANO_MES, MAX(DIA) AS MAX_DIA
FROM DL_RG_ANALYTICS.SH_CALENDARIO
GROUP BY 1
) B ON A.ANOMES = B.ANO_MES
) N
SET DIAS_AL_CIERRE = DIAS_AL_CIERRE_1;
What indexes are defined on the SH_CALENDARIO table? If there is a composite index of (ANO, MES) then you should re-write your LEFT JOIN sub-query to GROUP BY these two columns since you concatenate them together anyways. In general, you want to perform joins, GROUP BY and OLAP functions on indexes, so there will be less row re-distribution and they will run more efficiently.
Also, this query is updating all rows in the table with the same value. Is this intended, or do you want to include extra columns in your WHERE clause?
From a dataset character that has a name column, I want to query the two names in with the shortest and longest names, as well as their respective lengths and when there is more than one smallest or largest name, I choose the one that comes first when ordered alphabetically.
With that query, I get all the shortest and longest names (A)
SELECT
name, LENGTH(name) AS LEN
FROM
character
WHERE
length(name) = (SELECT MAX(LENGTH(name)) FROM character)
OR length(name) = (SELECT MIN(LENGTH(name)) FROM character)
With this one, I get all the shortest names except the first alphabetically ordered one (B)
SELECT
name, LENGTH(name) AS LEN
FROM
character
WHERE
length(name) = (SELECT MIN(LENGTH(name)) FROM character)
ORDER BY
name DESC
LIMIT 10 OFFSET 2;
When I try to remove B from A
A EXCEPT B
I would expect to keep the first shortest name but It does not appear.
I would use ROW_NUMBER here:
WITH cte AS (
SELECT *, ROW_NUMBER() OVER (ORDER BY LENGTH(name), name) rn_min,
ROW_NUMBER() OVER (ORDER BY LENGTH(name) DESC, name) rn_max
FROM character
)
SELECT name, LENGTH(name) AS LEN
FROM cte
WHERE 1 IN (rn_min, rn_max)
ORDER BY LENGTH(name);
When you set OFFSET 2 in your B query, you don't get:
all the shortest names except the first 1 alphabetically ordered
Instead you get:
all the shortest names except the first 2 alphabetically ordered,
because this is what OFFSET 2 does: it skips the first 2 rows.
Also another problem with your code is the ORDER BY clause in your B query.
If you have this:
SELECT name,LENGTH(name) AS LEN FROM character
WHERE length(name) = (select max( LENGTH(name)) from character )
or length(name) = (select min( LENGTH(name)) from character)
EXCEPT
SELECT name,LENGTH(name) AS LEN FROM character
WHERE length(name) = (select min( LENGTH(name)) from character)
ORDER BY name desc LIMIT 10 OFFSET 2;
you may think that the ORDER BY clause (and LIMIT and OFFSET) is applied only to your B query, but this is not how it is interpreted.
Actually ORDER BY (and LIMIT and OFFSET) is applied to the whole query after the rows are returned.
To get the results that you want by using code similar to yours you must use a subquery to wrap your B query, like this:
SELECT name,LENGTH(name) AS LEN FROM character
WHERE length(name) = (select max( LENGTH(name)) from character )
or length(name) = (select min( LENGTH(name)) from character)
EXCEPT
SELECT * FROM (
SELECT name,LENGTH(name) AS LEN FROM character
WHERE length(name) = (select min( LENGTH(name)) from character)
ORDER BY name desc LIMIT 10 OFFSET 1
)
I have the following query:
SELECT * from tWords where WordAton IN ("bbb", "aaa2", "ccc", "aaa1")
the query returns first the results for "aaa1" then for "aaa2" then for "bbb" and then for "ccc". Is there a way to return the results in the order of the input array, which means first the results for "bbb" then for "aaa2"... etc.
Thank you in advance.
You can apply conditional ordering like this:
SELECT *
from tWords
where WordAton IN ('bbb', 'aaa2', 'ccc', 'aaa1')
order by case WordAton
when 'bbb' then 1
when 'aaa2' then 2
when 'ccc' then 3
when 'aaa1' then 4
end
In SQL (not just SQLite), the only way to always return rows in a given order is with a SQL ORDER BY ... clause. So the short answer is, "No", there's no simple way to return rows in the order given by the contents of an IN (...) clause.
You could use a common table expression (CTE) to define a sort order, but that's usually not worth the trouble. This isn't the same thing as ordering by the contents of a IN (...) clause, but it looks the same. (You're ordering by the sort order specified in the CTE.)
with ordered_words as (
select 1 as sort_order, 'bbb' as WordAton union
select 2, 'aaa2' union
select 3, 'ccc' union
select 4, 'aaa1'
)
select t.WordAton
from tWords t
join ordered_words o on t.WordAton = o.WordAton
where t.WordAton in ('bbb', 'aaa2', 'ccc', 'aaa1')
order by o.sort_order;
I want to sort semicolon separated values per row in a column. Eg.
Input:
abc;pqr;def;mno
xyz;pqr;abc
abc
xyz;jkl
Output:
abc;def;mno;pqr
abc;pqr;xyz
abc
jkl;xyz
Can anyone help?
Perhaps something like this. Breaking it down:
First we need to break up the strings into their component tokens, and then reassemble them, using LISTAGG(), while ordering them alphabetically.
There are many ways to break up a symbol-separated string. Here I demonstrate the use of a hierarchical query. It requires that the input strings be uniquely distinguished from each other. Since the exact same semicolon-separated string may appear more than once, and since there is no info from the OP about any other unique column in the table, I create a unique identifier (using ROW_NUMBER()) in the most deeply nested subquery. Then I run the hierarchical query to break up the inputs and then reassemble them in the outermost SELECT.
with
test_data as (
select 'abc;pqr;def;mno' as str from dual union all
select 'xyz;pqr;abc' from dual union all
select 'abc' from dual union all
select 'xyz;jkl' from dual
)
-- End of test data (not part of the solution!)
-- SQL query begins BELOW THIS LINE.
select str,
listagg(token, ';') within group (order by token) as sorted_str
from (
select rn, str,
regexp_substr(str, '([^;]*)(;|$)', 1, level, null, 1) as token
from (
select str, row_number() over (order by null) as rn
from test_data
)
connect by level <= length(str) - length(replace(str, ';')) + 1
and prior rn = rn
and prior sys_guid() is not null
)
group by rn, str
;
STR SORTED_STR
--------------- ---------------
abc;pqr;def;mno abc;def;mno;pqr
xyz;pqr;abc abc;pqr;xyz
abc abc
xyz;jkl jkl;xyz
4 rows selected.