I need a Query that without any changes work on these three different database server : MySQL, MSSQL, PostgreSQL .
In this query i have to to calculate a column with the following expression that work correctly on MySQL :
COUNT(DISTINCT field_char,field_int,field_date) AS costumernum
The fields in the distinct are of different type :
field_char = character
field_int = integer
field_date = datetime
The expression is inside a parent query select, so if i try to achieve the result with a sub query approach, i stumble in this situation :
SELECT t0.description,t0.depnum
(select count(*) from (
select distinct f1, f2, f3 from salestable t1
where t1.depnum = t0.depnum
) a) AS numitems
FROM salestable t0
I get an error with this query, how can i get the value of the parent query ?
The expression work correctly on MySQL but i get an error when i try to execute it on Sql Server or PostgreSQL (the problem is that the count function doesn't accept 3 arguments of different type on MSSQL/PostgreSQL), is there a way to achieve the same result with an expression that work in each of these database server (SQL Server, MySQL, PostgreSQL ) ?
A general way to do this on any platform is as follows:
select count(*) from (
select distinct f1, f2, f3 from table
) a
Edit for new info:
What if you try joining to the distinct list (including the dept) and then doing the count? I created some test data and this seems to work. Make sure the COUNT is on one of the t1 columns - otherwise it will mistakenly return 1 instead of 0 when there are no corresponding entries in t1.
SELECT t0.description, t0.depnum, count(t1.depnum) as 'numitems'
FROM salestable t0
LEFT JOIN (select distinct f1,f2,f3,depnum from salestable) t1
ON t0.depnum = t1.depnum
GROUP BY
t0.description, t0.depnum
How about concatenating?
COUNT(DISTINCT field_char || '.' ||
cast(field_int as varchar) || '.' ||
cast(field_date as varchar)) AS costumernum
Warning: your concatenation operator may vary with RDBMS flavor.
Update
Apparently, the concatenation operator portability is question by itself:
String concatenation operator in Oracle, Postgres and SQL Server
I tried to help you with the distinct issue.
Related
I have a question similar to the one found here: How to find rows in SQL that start with the same string (similar rows)?, and this solution works in MySQL 5.6 but not 5.7.
I have a database (t) with multiple columns, the important ones being id and filepath, and what I am trying to accomplish is retrieving all the file paths which have the same last 5 characters. The following works in MySQL5.6, and the second SELECT works fine in 5.7:
SELECT id, filepath FROM t
WHERE SUBSTRING(filepath, -5) IN
(
SELECT SUBSTRING(filepath, -5)
FROM t
GROUP BY SUBSTRING(filepath, -5)
HAVING COUNT(*) > 1
)
But when I try to run it on 5.7 I get the error
Expression #1 of HAVING clause is not in GROUP BY clause and contains
nonaggregated column 't.filepath' which is not functionally dependent on
columns in GROUP BY clause; this is incompatible with
sql_mode=only_full_group_by
Sample data:
id filepath
1 /Desktop/file1.txt
2 /Desktop/file2.txt
3 /Desktop/file1.txt
and I would want to return the rows with id 1 and 3. How can I fix this for MySQL5.7?
EDIT: Also can anybody point me in the right direction for the SQL to remove the duplicates? So I would want to remove the entry for id 3 but keep the entry for id 1 and 2.
Please read the mysql documentation on the subject GROUP BY and sql_mode only_full_group_by (like your error message says):
https://dev.mysql.com/doc/refman/5.7/en/group-by-handling.html
I think changing the inner query to this might fix the problem:
SELECT SUBSTRING(filepath, -5) AS fpath
FROM t
GROUP BY fpath
HAVING COUNT(fpath) > 1
Edit:
As to your question of why adding the "AS fpath" works:
Adding the alias "fpath" is just a clean way to do this. The point of ONLY_FULL_GROUP_BY is that each field you use in the SELECT, HAVING, or ORDER BY must also be in the GROUP BY.
So I added the fpath-alias for multiple reasons:
For performance: The query you wrote had SUBSTRING(filepath, -5) twice, which
is bad for performance. Mysql has to execute that SUBSTRING call twice,
while in my case it has to do it only once (per row).
To fix the group-by issue: You had COUNT() in the having, but "" was not in your GROUP BY statement (I'm not even sure whether that would be possible). You had to count "something", so since "fpath" was in your SELECT and in your GROUP BY, using that as your COUNT() would fix the problem.
I prefer not to put subqueries in an IN() predicate because MySQL tends to run the subquery many times.
You can write the query differently to put the subquery in the FROM clause as a derived table. That will make MySQL run the subquery just once.
SELECT id, filepath
FROM (
SELECT SUBSTRING(filepath, -5) AS suffix, COUNT(*) AS count
FROM t
GROUP BY suffix
HAVING count > 1
) AS t1
JOIN t AS t2 ON SUBSTRING(t2.filepath, -5) = t1.suffix
This is bound to do a table-scan though, so it's going to be a costly query. It can't use an index when doing a substring comparison like that.
To optimize this, you might create a virtual column with an index.
ALTER TABLE t
ADD COLUMN filepath_last VARCHAR(10) AS (SUBSTRING_INDEX(filepath, '/', -1)),
ADD KEY (filepath_last);
Then you can query it like this, and at least the subquery uses an index:
SELECT id, filepath
FROM (
SELECT filepath_last, COUNT(*) AS count
FROM t
GROUP BY filepath_last
HAVING count > 1
) AS t1
STRAIGHT_JOIN t AS t2 ON t2.filepath_last = t1.filepath_last
The solution that ended up working for me was found here: Disable ONLY_FULL_GROUP_BY
I ran SELECT ##sql_mode then SET ##sql_mode = followed by a string containing all the values returned by the first query except for only_full_group_by, but I'm still interested in how this is to be accomplished without changing the SQL settings.
Is it possible to make a query that changes the where clause acording to some condition? For instance I want to select * from table1 where data is 19/July/2016 but if field id is null then do nothing, else compare id to something else. Like the query bellow?
Select * from table1 where date="2016-07-19" if(isnull(id),"",and id=(select * from ...))
Yes. This should be possible.
If we assume that date and id are references to columns in (the unfortunately named) table table1, if I'm understanding what you are attempting to achieve, we could write a query like this:
SELECT t.id
, t.date
, t....
FROM table1 t
WHERE t.date='2016-07-19'
AND ( t.id IS NULL
OR t.id IN ( SELECT expr FROM ... )
)
It would also be possible to incorporate the MySQL IF() and IFNULL() functions, if there's some requirement to do that.
As far as dynamically changing the text of the SQL statement after the statement is submitted to the database, no, that's not possible. Any dynamic changes to the SQL text would need to be done when the SQL statement is generated, before it is submitted to the database.
My personal preference would be to use a join operation rather than a IN (subquery) predicate.
I think you're trying too hard. If id is NULL that's equivalent to having a FALSE in the where clause. So:
Select * from table1 where date="2016-07-19" and id=(select * from ...)
Should only match the records you want. If id is NULL you get nothing.
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 need to get the count(calmness) from a table entity_epoch_data in mysql twice :
where column of calmness>0 and calmness<0
so now I connect to database twice as follow:
SELECT count(calmness) FROM omid.entity_epoch_data where calmness<0;
SELECT count(calmness) FROM omid.entity_epoch_data where calmness>=0;
I am wondering if I can combine these two query and get the result back as one table with one connection?
I tried this but did not work:
select c1,c2 from (
SELECT count(calmness) as c1 FROM omid.entity_epoch_data where calmness<0,
SELECT count(calmness) as c2 FROM omid.entity_epoch_data where calmness>=0);
Can anyone help?
This can be done by using SUM() with an expression,when using SUM() within expression it evaluates it to true/false i.e 1/0 based on the result of expression ,note you using aggregate function without grouping them this will result in a single row
SELECT
SUM(calmness < 0) c1,
SUM(calmness >= 0) c2
FROM omid.entity_epoch_data ;
I've got a column "code" which may have a string of multiple values e.g. "CODE1&CODE2"... I just need the first one for my JOIN ... kind of like code.split("&")[0]
SELECT myTable.*, otherTable.id AS theID
FROM myTable INNER JOIN otherTable
ON myTable.(+++ code before the & +++) = otherTable.code
The value in myTable may also just be CODE1
SUBSTRING_INDEX will do exactly what you want - return the substring of your column up to the specified character:
SELECT
myTable.*,
otherTable.id AS theID
FROM myTable
INNER JOIN otherTable
ON SUBSTRING_INDEX(myTable.code, '&', 1) = otherTable.code
More info at: http://dev.mysql.com/doc/refman/5.0/en/string-functions.html
And here's a fiddle demoing it: http://sqlfiddle.com/#!2/96a6e/2
Please note that this will be SLOW if you're joining many columns. You're not only eliminating the possibility of using an index, but performing a very slow string operation on every comparison. I wouldn't suggest using this on very large tables. If your data set is huge, you may want to consider rearchitecting your DB.