Is there a way to pass an array into a MySQL query and return the results as another array ?(apart from using cursors which would be an overkill for my use case)
For a single id, my query looks like this.
SET #userId = '04b452cd59dcc656'
Select user_account_number from userstore where u_id = #userId ;
Instead of sending each id at a time, I am trying to send a list and return a list
SET #userId = ('04b452cd59dcc656','eqwe52cddasfsd656');
<query returning the list of account numbers>
Also - I think this would be efficient over just sending one id at a time. Thoughts ?
You can use IN:
select user_account_number
from userstore
where u_id in ('04b452cd59dcc656', 'eqwe52cddasfsd656') ;
Using variables is trickier. If you know a maximum number, you can do:
select user_account_number
from userstore
where u_id in (#id1, #id2);
Not satisfying, but it does the job. Similarly unsatisfying is FIND_IN_SET():
set #ids = '04b452cd59dcc656,eqwe52cddasfsd656';
select user_account_number
from userstore
where find_in_set(u_id, #ids) > 0;
Alas, this won't use an index.
Finally there is dynamic SQL:
set #sql = concat('select user_account_number from userstore where u_id in (''',
replace(ids, ',', ''','''),
''')'
);
prepare s from #sql;
execute s;
Related
Is there a way to do the following in mysql?
SET #studios = ('Disney', 'Warner Bros.', 'Fox');
SELECT * FROM movies WHERE provider IN #studios;
When I try doing the above I get the error:
Operand should contain 1 column(s)
The error is coming from your initial assignment. You cannot assign lists to variables.
The only way of doing this in MySQL is to either create a temp table to hold the values, and then do ... IN (SELECT someVal FROM thatTemp), or to dynamically create the query with the values directly in the query string.
Example temp table creation:
CREATE TEMPORARY TABLE `someTemp` ( someVal VARCHAR(16) );
INSERT INTO `someTemp` (someVal) VALUES ('a'), ('b'), ('c');
SELECT * FROM myTable WHERE myField IN (SELECT someVal FROM someTemp);
DELETE TEMPORARY TABLE `someTemp`;
Alternatively, there is also FIND_IN_SET, which could be used like this:
SET #list = 'a,b,c';
SELECT * FROM myTable WHERE FIND_IN_SET(myField, #list) <> 0;
but this method probably has extremely poor performance (and may not be useable if your "myField" values may contain commas).
It is not possible to set a tuple/list/array in a user-defined variable in MySQL. You can use Dynamic SQL for the same:
-- we use single quotes two times to escape it
SET #studios = '(''Disney'', ''Warner Bros.'', ''Fox'')';
-- generate the query string
SET #query = CONCAT('SELECT * FROM movies WHERE provider IN ', #studios);
-- prepare the query
PREPARE stmt FROM #query;
-- execute it
EXECUTE stmt;
-- deallocate it
DEALLOCATE PREPARE stmt;
You could concatenate your list to a string, and use FIND_IN_SET as your criteria. Might not be super efficient, but makes the code quite easy to read and maintain.
Looks like this:
SET #studios = CONCAT_WS(',',
'Disney',
'Warner Bros.',
'Fox'
);
SELECT * FROM movies
WHERE FIND_IN_SET(provider, #studios) <> 0;
I have been trying to create a simple loop of SELECT statements in MySQL to reduce code. I have started this using CONCAT() however this causes the procedure to stop/fail. For example (where k is a loop counter):
CONCAT('SELECT (Child_', k, ' INTO #Age_Child_', k, ' FROM lookup_childage WHERE ModYear = ModYear_var LIMIT 1)');
To diagnose the issue, I simply tried to place the SELECT statement (without concatenated loop variables) inside a string to then be executed. While I could get this to work for simple statements it would not work for the following:
SET #queryString = CONCAT('SELECT Child_1 INTO #Age_Child_1 FROM lookup_childage WHERE ModYear = ModYear_var LIMIT 1');
PREPARE stmt FROM #queryString;
EXECUTE stmt;
Does anyone know why the #queryString containing the CONCAT() statement will not be executed/cause the procedure to fail?
tl;dr The statement you're trying to write has the form SELECT(rest of statement) LIMIT 1. It should have the form SELECT rest of statement LIMIT 1.
It looks like you want to create variable column names, ummm, because your lookup_childage table is denormalized. I guess that table has these columns.
Child_1 INT
Child_2 INT
Child_3 INT
Child_4 INT
It looks like you hope to get a #queryString value containing this sort of thing:
SELECT Child_4 INTO #Age_Child_4 FROM lookup_childage WHERE ModYear = ModYear_var LIMIT 1
Only the 4s are variable.
So to get that string you want
SELECT CONCAT('SELECT Child_', k,
' INTO #Age_Child_', k,
' FROM lookup_childage WHERE ModYear = ModYear_var LIMIT 1'
)
INTO #queryString;
I have a Users table and I'm getting user details (usual way) with id.
This is how I'm getting user details;
select id,kullaniciadi,FotoGet(K.Foto,K.Gender) from kullanicilar K where id=1;
FotoGet function always returning string value like 'Photos/ssss.jpg'
So far I have not trouble to use this way but I'm wondering how can I do this with a single function?
Like
set #uid=1;
Select UserGet(#uid);
I will put the id inside parentheses and the function will run my select query and return all user detail columns. id, kullaniciadi, FotoGet(K.id,K.Foto,K.Gender)
Can I use this way to get details?
A MySQL stored function cannot return multiple columns, it can only return a single scalar value.
But you could design a stored procedure that returns a result set:
CREATE PROCEDURE UserGet(uid INT)
SELECT id, kullaniciadi, FotoGet(K.Foto,K.Gender) FROM kullanicilar K WHERE id=uid;
Then call it like so:
CALL UserGet(1234);
It returns a result set just like a SELECT query would.
DELIMITER //
CREATE PROCEDURE UserGet(IN uid INT, IN column_name VARCHAR(64))
BEGIN
SET #sql = CONCAT('SELECT id, ', column_name, ' FROM kullanicilar K WHERE id=?');
PREPARE stmt FROM #sql;
SET #uid = uid;
EXECUTE stmt USING #uid;
END//
DELIMITER ;
Call it like so:
CALL UserGet(1234, 'kullaniciadi');
Remember that it's your responsibility to write code to pass a valid column name as the procedure argument. If you allow untrustworthy content to be passed, then it might be an SQL injection vulnerability.
Re your additional comment:
This should work fine:
CALL UserGet(1234, 'FotoGet(Foto,Gender)');
Is it possible to query a table whose name comes from a sub-query?
For example.,
SELECT * FROM <TABLE_NAME IS <SUB_QUERY>>
select * from (
(select distinct(name) from category where id = 3 limit 1) CAT);
INNER QUERY RESULTS --> DEPARTMENT;
So it has to fetch from department table.
Using Mysql as DB.
You should use Prepared Statements.
In your case it should be:
select #name := name from (
(select distinct(name) from category where id = 3 limit 1) CAT);
set #sqlquery := 'select * from ' . #name ;
prepare qry from #sqlquery ;
execute qry;
deallocate prepare qry;
This might be helpful SQL Syntax for Prepared Statements
In two words: you can execute sql commands specified in varchar variables which can be produced by concatenation and other stuff.
I have stored procedure in my database and i need to look up a table and cross reference an id, then using the returned row i need to insert information into another table, but i cant seem to use the infomation from the lookup into the insert. This is what i have..
BEGIN
#Routine body goes here...
SET #UID = uid;
SET #UIDTOFB = uid_to;
SET #SQLTEST = CONCAT('SELECT users.user_auto_id FROM users WHERE users.user_fb_uid= #UIDTOFB LIMIT 1');
PREPARE sqlcmd from #SQLTEST;
EXECUTE sqlcmd;
INSERT INTO challenges(challenge_from_uid, challenge_to_uid, challenge_dateadded) VALUES(#UID, #SQLTEST.users.user_auto_id, now());
SET #LASTID = LAST_INSERT_ID();
SELECT #LASTID as id;
END
any help would be much appreciated!
This won't insert the value of #UIDTOFB since you missed some '. It takes this whole statement as one string and therefore the statement fails.
SET #SQLTEST = CONCAT('SELECT users.user_auto_id FROM users WHERE users.user_fb_uid= #UIDTOFB LIMIT 1');
PREPARE sqlcmd from #SQLTEST;
EXECUTE sqlcmd;
Anyway I'd recommend you use parameters like this:
PREPARE sqlcmd from 'SELECT users.user_auto_id FROM users WHERE users.user_fb_uid= ? LIMIT 1';
EXECUTE sqlcmd USING #UIDTOFB;
You can read more about it here in the manual.
UPDATE: Now I get, what you want to do. Do it simply like this:
SELECT #anyVariable:=users.user_auto_id FROM users WHERE users.user_fb_uid= #UIDTOFB LIMIT 1;
INSERT INTO challenges(challenge_from_uid, challenge_to_uid, challenge_dateadded) VALUES(#UID, #anyVariable, now());