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;
Related
I have a MySQL stored procedure (shown below) that's supposed to build a list of IDs from a table of hierarchically related records. I'm having to re-engineer an older stored procedure to switch from using a simple CONCAT function to GROUP_CONCAT because the former couldn't handle the sizes of the lists being generated (i.e., the lists are going well over the 1024 character limit of the CONCAT function).
DELIMITER $$
CREATE PROCEDURE SPTest (top_id INT)
BEGIN
DECLARE ids_all TEXT;
SET SESSION group_concat_max_len = 1000000;
SET ids_all = top_id;
SET #str = GROUP_CONCAT('SELECT GROUP_CONCAT(id SEPARATOR \', \') ',
'FROM tbl WHERE nha_id = ', top_id, ' INTO #ids_tmp' SEPARATOR '');
PREPARE stmt FROM #str;
EXECUTE stmt;
WHILE #ids_tmp != "" DO
SET ids_all = GROUP_CONCAT(ids_all, #ids_tmp SEPARATOR ', ');
SET #str = GROUP_CONCAT('SELECT GROUP_CONCAT(id SEPARATOR \', \') ',
'FROM tbl WHERE nha_id IN (', #ids_tmp, ') INTO #ids_tmp' SEPARATOR '');
PREPARE stmt FROM #str;
EXECUTE stmt;
END WHILE;
SELECT ids_all AS ids;
END $$
DELIMITER ;
The problem is this routine is generating the following error when I try to call it (and sometimes it returns this error when I try to create the Stored Procedure):
ERROR 1111 (HY000): Invalid use of group function
When I manually create the same kinds of queries this code would build and run them at the command-line, they work perfectly fine -- no errors of any kind, and I get the results I expect. I've seen posts (both here on Stack Exchange and elsewhere) which say that MySQL doesn't support nested aggregate functions, but the concatenation here is just being done to strings. So I thought that maybe somehow it was seeing the GROUP_CONCAT in the string and burping because of that, so I tried putting "XXXX" in place of "GROUP_CONCAT" in the string and then using the REPLACE function to switch it back, but that made no difference. I also tried it with WHERE and HAVING for the criteria clause, but neither one worked. I've also done an extensive web search and was unable to find anything that was in any way helpful.
I don't know what else to try, mainly because I can't see what's wrong with the syntax here. Any help would be appreciated.
Update 1:
I have since tried a modified version of the script where the GROUP_CONCAT merges data from a subquery like this:
SET #qrystr = GROUP_CONCAT('SELECT GROUP_CONCAT(c SEPARATOR ", ") ',
'FROM (SELECT id AS c FROM tbl WHERE nha_id IN (', #ids_tmp,
') AS d INTO #ids_tmp' SEPARATOR '');
but that made no difference either.
You can't use GROUP_CONCAT() as a scalar function; it must be used in the context of a set of rows. Similarly, you can't use any other aggregate function without a table reference:
SET #x = MAX(<expr>); -- makes no sense
Ideally you should upgrade to MySQL 8.0 if you haven't already, and use a recursive CTE query instead:
WITH RECURSIVE hierarchy AS (
SELECT top_id AS id
UNION
SELECT tbl.id FROM tbl JOIN hierarchy ON tbl.nha_id = hierarchy.id
)
SELECT GROUP_CONCAT(id SEPARATOR ', ') AS ids_all FROM hierarchy;
That would eliminate the need for using loops or prepare/execute or temp variables.
Thanks to Bill Karwin's answer regarding the need to use SELECT with GROUP_CONCAT, I was able to see how my code needed to be changed. Rather than using a SET statement to assign the values to the variables, I need to use a SELECT ... INTO ... construct, as shown here:
DELIMITER $$
CREATE PROCEDURE ASSEMBLY_LIST_TEST (top_id INT)
BEGIN
DECLARE ids_all TEXT DEFAULT '';
SET SESSION group_concat_max_len = 1000000;
SET ids_all = top_id;
# Find the 1st-level children of 'top_id' to start building the list
SELECT GROUP_CONCAT('SELECT GROUP_CONCAT(id SEPARATOR ", ") FROM tbl ',
'WHERE nha_id = ', top_id, ' INTO #ids_tmp' SEPARATOR '') INTO #qrystr;
PREPARE stmt FROM #qrystr;
EXECUTE stmt;
# Recursively find the children of each level of children of the previous loop & add to the list
WHILE #ids_tmp != '' DO
SELECT GROUP_CONCAT(ids_all, ', ', #ids_tmp SEPARATOR '') INTO ids_all;
SELECT GROUP_CONCAT('SELECT GROUP_CONCAT(id SEPARATOR ", ") FROM tbl ',
'WHERE nha_id IN (', #ids_tmp, ') INTO #ids_tmp' SEPARATOR '') INTO #qrystr;
PREPARE stmt FROM #qrystr;
EXECUTE stmt;
END WHILE;
SELECT ids_all AS ids;
END $$
DELIMITER ;
This now produces exactly the result I was looking for. Of course, the recursive query approach is a much better solution for what I want this to do, but maybe my solution will help someone else.
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 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)');
I've got MySQL procedure which I execute in MySQL Workbench. The problem is that it generates many new result-set, and GUI client show it (...many times) -
I found solution, which I can use instead just select clause to avoid generating result-sets. It looks like:
SELECT EXISTS(
SELECT ...
)
INTO #resultNm
Unfortunately it won't work with LIMIT ?,1 where ? is my variable 'i'. I also cant use just 'i' instead % because I am working on MySQL 5.1 (and limit clauses can't be done in other way). So my question - are other possibilities to hide result-sets?
CREATE PROCEDURE LOOPDOSSIERS(starter integer, finish integer)
BEGIN
DECLARE n INT DEFAULT 0;
DECLARE i INT DEFAULT 0;
DECLARE row_oid binary(16);
DECLARE row_str VARCHAR(256);
DECLARE row_old VARCHAR(256);
SET i=starter;
WHILE i<finish DO
-- SET row_str = ();
SET #row_str = 'select CAST(concat(d.prefixe_numero,d.numero) as CHAR) from courrier_concerne_dossier as x
join dossier as d on
d.oid = x.dossier_oid limit ?,1';
PREPARE stmt1 FROM #row_str;
EXECUTE stmt1 USING #i;
SET #row_oid = 'select x.courrier_oid
from courrier_concerne_dossier as x
join dossier as d on
d.oid = x.dossier_oid LIMIT ?,1';
PREPARE stmt2 FROM #row_oid;
EXECUTE stmt2 USING #i;
select dossiers_str from courrier_envoye where oid = row_oid into row_old;
update courrier_envoye set dossiers_str = CAST(CONCAT(row_str, " ", row_old) AS CHAR) where oid = row_oid;
SET i = i + 1;
END WHILE;
End;
;;
LIMIT without an ORDER BY clause doesn't have a well defined behavior. For your parameters to work in a sensible way, you'll need to order by something. The starter and finish variables aren't very meaningful at the moment, but it's currently not clear what they're intended to be.
I think you can probably accomplish this whole procedure in a single query using the syntax in this answer (also probably much faster). That probably won't work with LIMIT, but I'd highly recommend using a range of some kind in the where clause rather than a limit anyway.
I'm quite new to subject of writting stored function for mySQL database, hence i'm not sure if what i'm trying to do here is possible at all.
I need a function that will return a column from random row from a table. I don't want to use ORDER BY RAND() method to do that, rather i would do this like this:
DECLARE MAX_COUNT INT DEFAULT 120000;
DECLARE rand_offset INT;
DECLARE str_rnd_word VARCHAR(255);
SET rand_offset = FLOOR((RAND() * MAX_COUNT));
SELECT word INTO str_rnd_word FROM all_words LIMIT 1 OFFSET rand_offset ;
RETURN str_rnd_word;
MySQL throws an error upon creating function with body like that. But when I use hard-coded number as OFFSET it works just fine.
Can someone shed some light on the subject please.
I'm running MySQL 5.0.45 on windows box.
Thanks
In MySQL before 5.5, you can't put a variable into the LIMIT clause in MySQL stored procedures. You have to interpolate it into a string and then execute the string as a dynamic query.
SET rand_offset = FLOOR(RAND() * (SELECT COUNT(*) FROM all_words));
SET #sql = CONCAT('SELECT word INTO str_rnd_word FROM all_words LIMIT 1 OFFSET ', rand_offset);
PREPARE stmt1 FROM #sql;
EXECUTE stmt1;