I am quite new about queries and I would like to know if there is an easier solution for the query I am working on.
For instance I want to get the data where x is 5,7,9,11,13,15 and 17.
I have a query like below;
SELECT * FROM abc WHERE x = 5 or x = 7 or x = 9 or x = 11 or x = 13 or x = 15 or x = 17;
Is it okay to use this query or are there any other simpler and efficient solution?
EDIT
Does it affect the perfomance when I use x=[5,7,8,11,13,15,17] vs x=[5,11,7,15,8,17,13]
X is the ID of another category for instance.
This is shorter but performs equally
SELECT * FROM abc WHERE x in (5,7,9,11,13,15,17)
But remember if one entry in the in clause is null then it returns FALSE.
Related
My problem is how to loop through a table and extract information from another table.
I have a table - X with 470 records:
A B C
111 12 18
121 21 29
127 37 101
I would like to write the following query:
create or replace view NEW as
For j = 1-3
Select * from Y
where imei = X.A(j) and id > X.B(j) and id < X.C(j)
Apologies, I am a matlab programmer so I have used that syntax above to explain what I want. How can I do this in MySql? I have looked up For Loops but mostly it loops through within the same table. I need to loop through a different table and use those criteria in the where statement of a different table.
To get 3 rows from a table, use LIMIT 3 in a subquery. To get related rows in another table, use JOIN.
CREATE OR REPLACE VIEW new AS
SELECT Y.*
FROM Y
JOIN (SELECT *
FROM X
LIMIT 3) AS X ON Y.ime1 = X.a AND Y.id > X.b AND Y.id < X.c
To make LIMIT 3 produce predictable results, you should have an ORDER BY clause in the subquery. Otherwise, it will select an arbitrary set of 3 rows from X.
Trying to wrap my head around how to do this query - I want to return a list of client records and need to exclude clients if they had only a specific value and no other values.
For example
c# value
1 X
1 Y
2 X
3 Y
I want all the records for clients 1 and 3, since they had a value other than X. I do not want client 2, because that client had ONLY X.
I for example want returned in this case:
1 X
1 Y
3 Y
Of course, I could have lots of other records with other client id's and values, but I want to eliminate only the ones that have a single "X" value and no other values.
Maybe using a sub-query?
Try this:
SELECT client, value FROM myTable where `client` in
(select distinct(client) from myTable where value !='X');
Returns:
Client Value
1 X
1 Y
3 Y
Something like this
SELECT ABB2.*
FROM
mytable AS ABB2
JOIN
(SELECT c
FROM mytable
WHERE value <> "X"
GROUP BY c) AS ABB1 ON ABB1.c = ABB2.c
GROUP BY ABB2.c, ABB2.value
It's faster than using a WHERE clause to identify the sub query results (as in Mike's answer)
I am trying to update my table like this:
Update MyTable
SET value = 1
WHERE game_id = 1,
x =-4,
y = 8
SET value = 2
WHERE game_id = 1,
x =-3,
y = 7
SET value = 3
WHERE game_id = 2,
x = 5,
y = 2
I can do a foreach() but that will send over 50 separate Queries which is very slow.
That's why I want it to be combined into 1 big Query.
( I do use an id for each row but the combination of game_id, x and y is what I use to Identify the row I need. )
The update_batch() function from codeIgniter described here:
Update batch with CodeIgniter
was helpful and almost perfect but it only allows for 1 single where clause, you cannot (as far as I understood and tried) enter an array with multiple where clauses.
I've also checked out this question:
MYSQL UPDATE SET on the Same Column but with multiple WHERE Clauses
But it only allows for multiple row updates containing only a single different WHERE clause and I need multiple WHERE clauses! :)
Anwsers can be in simple SQL or with the use of php (and CodeIgniter) or in a different way. I'd this problem to be solved in any possible way ;)
I can really use the advice/help! =D
give this a try by using CASE
Update MyTable
SET value = CASE
WHEN game_id = 1 AND x = -4 AND y = 8 THEN 1
WHEN game_id = 1 AND x = -3 AND y = 7 THEN 2
WHEN game_id = 2 AND x = 5 AND y = 2 THEN 3
ELSE value
END
WHERE game_ID IN (1,2,3) AND -- the purpose of this WHERE clause
x IN (-4, -3, 5) AND -- is to optimize the query by preventing from
y IN (8,7,2) -- performing full table scan.
This question already has an answer here:
Update multiple rows with multiple 'where' clauses for each individual row
(1 answer)
Closed 9 years ago.
I am trying to update my table like this:
Update MyTable
SET value = 1
WHERE game_id = 1,
x =-4,
y = 8
SET value = 2
WHERE game_id = 1,
x =-3,
y = 7
SET value = 3
WHERE game_id = 2,
x = 5,
y = 2
I can do a foreach() but that will send over 50 separate Queries which is very slow.
That's why I want it to be combined into 1 big Query.
( I do use an id for each row but the combination of game_id, x and y is what I use to Identify the row I need. )
The update_batch() function from codeIgniter described here:
Update batch with CodeIgniter
was helpful and almost perfect but it only allows for 1 single where clause, you cannot (as far as I understood and tried) enter an array with multiple where clauses.
I've also checked out this question:
MYSQL UPDATE SET on the Same Column but with multiple WHERE Clauses
But it only allows for multiple row updates containing only a single different WHERE clause and I need multiple WHERE clauses! :)
Anwsers can be in simple SQL or with the use of php (and CodeIgniter) or in a different way. I'd this problem to be solved in any possible way ;)
I can really use the advice/help! =D
EDIT:
Sorry the question wasn't clear enough, I just changed it!
It seems me you need the logical operator AND:
UPDATE MyTable
SET value = 1
WHERE game_id = 1
AND x = -4
AND y = 8
I'm not familiar with the multiple WHERE clauses how you have it laid out, why not just do
UPDATE MyTable
SET value = 1
WHERE game_id = 1
AND x = -4
AND y = 8
A simple quiz:
Probably many guys know this before,
In my app there is a query in which Im using concat in where condition like this,
v_book_id and v_genre_id are 2 variables in my procedure.
SELECT link_id
FROM link
WHERE concat(book_id,genre_id) = concat(v_book_id,v_genre_id);
Now, I know there is a catch/bug in this, which will occur only twice in your lifetime. Can you tell me what is it?
I found this out yesterday and thought I should make a noise about all others practicing this.
Thanks.
Let's have a look
WHERE concat(book_id,genre_id) = concat(v_book_id,v_genre_id);
as opposed to
WHERE book_id = v_book_id AND genre_id = v_genre_id;
There. The second solution is
faster (optimal index usage)
easier to write (less code)
easier to read (what on earth was the author thinking to concatenate numbers???)
more correct (as Alnitak also stated in the question's comments). check out this sample data:
book_id | genre_id
1 | 12
11 | 2
Now add (or concat) v_book_id = 1 and v_genre_id = 12 and see how you'll get funny results with your concat() query
Note, some databases (including MySQL) allow operations on tuples, which may be what the clever author of the above really intended to do:
WHERE (book_id, genre_id) = (v_book_id, v_genre_id);
A working example of such a tuple predicate:
SELECT * FROM (
SELECT 1 x, 2 y FROM DUAL UNION ALL
SELECT 1 x, 3 y FROM DUAL UNION ALL
SELECT 1 x, 2 y FROM DUAL
) a
WHERE (x, y) = (1, 2)
Note, some databases will need extra parentheses around the right-hand side tuple : ((1, 2))