MySQL Stored Proc Variable returns NULL - mysql

Question

I have a stored proc that is setting one of the variables to NULL, though the query returns results.
Here is the SP:
CREATE DEFINER=`xxx`#`localhost` PROCEDURE `test`(IN CLIENT_ID INT)
BEGIN
DECLARE BEGIN_RANGE INT UNSIGNED DEFAULT 0;
select client_id into #CLIENT_ID3 from clients where
client_id = CLIENT_ID limit 1;
SET #BEGIN_RANGE = (select var_value from counter where var_name =
'latest_report_id_summarized' limit 1);
SELECT latest_invoice_id into #LATEST_INVOICE_ID from
SQL_AuditPro.clients where client_id = CLIENT_ID;
END
when I run the sp, then select the results :
select #CLIENT_ID3,#BEGIN_RANGE,#LATEST_INVOICE_ID;
I get :
12345,2342342234,NULL
I have also tried:
CREATE DEFINER=`xxx`#`localhost` PROCEDURE `test`(IN CLIENT_ID INT)
BEGIN
DECLARE BEGIN_RANGE INT UNSIGNED DEFAULT 0;
select client_id into #CLIENT_ID3 from clients
where client_id = CLIENT_ID limit 1;
SET #BEGIN_RANGE = (select var_value from counter where var_name =
'latest_report_id_summarized' limit 1);
SET #LATEST_INVOICE_ID = (SELECT latest_invoice_id from
SQL_AuditPro.clients where client_id = CLIENT_ID);
END
Same result. Obviously I don't need to SET #CLIENT_ID3 it was just in there for testing. Any ideas why this won't set the variable? When I run this query by itself I get a result, and if I run :
SELECT latest_invoice_id into #LATEST_INVOICE_ID from
SQL_AuditPro.clients where client_id = 12345;
select #LATEST_INVOICE_ID;
I get :
2342342234
I have tried declaring the variable, not declaring it, and it just seems like this variable seems to fall out of scope after the SP completes, yet the other two don't.
Thanks for any help you may be able to provide.

Answer 1

select client_id into #CLIENT_ID3 from clients where client_id = CLIENT_ID limit 1;
^---- missing #
SET #LATEST_INVOICE_ID = (SELECT [..snip..] where client_id = CLIENT_ID);
^--missing # as well
As written, both'll be intepreted as a self-equality test, e.g. where 1 = 1. There's no way for mysql to know that the client_id on EITHER side of the = is supposed to be the parameter you passed in to the stored proc, so both client_id will be treated as field names.
Since the second query is likely to return MULTIPLE rows of data, and you're trying to assign that result into a single variable, you'll get NULL as the result.

Answer 2

When you have defined arguments names to match with one or more of a table columns, then in your SQL statements you must use column qualifiers to differentiate with argument names. Otherwise, they will be treated and replaced as and by argument values;
See SQL Fiddle Example
In your case, as the condition client_id = CLIENT_ID was causing to (possibly) fetch multiple records, they are not assignable to a variable of non cursor type. Hence a NULL, the default value for user defined variables, was returned.
Change your procedure body as below:
CREATE DEFINER=`xxx`#`localhost` PROCEDURE `test`(IN CLIENT_ID INT)
BEGIN
DECLARE BEGIN_RANGE INT UNSIGNED DEFAULT 0;
select c.client_id into #CLIENT_ID3
from clients c
where c.client_id = CLIENT_ID limit 1;
SET #BEGIN_RANGE =
(select var_value
from counter
where var_name = 'latest_report_id_summarized' limit 1);
SET #LATEST_INVOICE_ID =
(SELECT c.latest_invoice_id
from SQL_AuditPro.clients c
where c.client_id = CLIENT_ID);
END