Asking about stored function in mysql - mysql

Question

drop function if exists rty_check_member_info_status;
DELIMITER $$
--
-- Functions
CREATE DEFINER=root#localhost FUNCTION rty_check_member_info_status(memb_id int,field_name_1 varchar(100),field_name_2 varchar(100),login_member_amount int(11),login_status char(1)) RETURNS char(1) CHARSET latin1
begin
declare fn_field_name_1 varchar(100) ;
declare fn_field_name_2 varchar(100) ;
declare fn_amount_for_profile_visible int(11);
declare fn_return char(1) default 'N';
declare test_field varchar(100);
select field_name_1,field_name_2,amount_for_profile_visible into
fn_field_name_1,fn_field_name_2,fn_amount_for_profile_visible
from member_account_settings inner join tbl_members on member_account_settings.member_auto_id = tbl_members.member_id
where tbl_members.member_id = memb_id ;
if fn_field_name_1 = 'H' Then
set fn_return = 'N' ;
else
if fn_field_name_2 = 'Y' Then
if fn_amount_for_profile_visible = '0' Then
set fn_return = 'Y' ;
else
if login_status = 1 Then
if fn_amount_for_profile_visible > login_member_amount Then
set fn_return = 'N' ;
else
set fn_return = 'Y' ;
end if;
else
set fn_return = 'N';
end if ;
end if;
else
set fn_return = 'Y';
end if ;
end if ;
return fn_return ;
end$$
DELIMITER ;

Answer 1

You're two choices are pretty much generated SQL(normally a bad idea because it's harder to write, debug and document) and using a case statement to select the column based on the name matching a string(which is normally a pretty good solution).
Here's an example of the second, since it's the solution I'd definitely recommend.
SET #test_field1 = "last_name_display_status" ;
SET #test_field2 = "last_name_display_for_other_partcpnt" ;
SELECT
CASE #test_field1
-- List columns here that you might want to return:
WHEN 'last_name_display_status' THEN last_name_display_status
WHEN 'last_name_display_for_other_partcpnt' THEN last_name_display_for_other_partcpnt
WHEN 'create_date' THEN create_date
-- Return a value for an invalid name here:
ELSE NULL
END AS test_field1,
CASE #test_field2
-- List columns here that you might want to return:
WHEN 'last_name_display_status' THEN last_name_display_status
WHEN 'last_name_display_for_other_partcpnt' THEN last_name_display_for_other_partcpnt
WHEN 'create_date' THEN create_date
-- Return a value for an invalid name here:
ELSE NULL
END AS test_field2,
-- Rest of select unaffected by this change
amount_for_profile_visible
INTO
fn_field_name_1,
fn_field_name_2,
fn_amount_for_profile_visible
FROM member_account_settings
INNER JOIN tbl_members
ON member_account_settings.member_auto_id = tbl_members.member_id
WHERE
tbl_members.member_id = memb_id
;
And for the sake of completeness a copy of the first solution I proposed(the generated SQL):
-- Need to use #vars, since named vars aren't in scope for the generated SQL:
SET #output1 = '';
SET #output2 = '';
SET #output3 = '';
SET #input1 = memb_id;
-- We also need to store our generated SQL to a variable
SET #query = 'SELECT ' + #test_field1 + ',' + #test_field2 + ', amount_for_profile_visible INTO #output1, #output2, #output3 FROM member_account_settings INNER JOIN tbl_members ON member_account_settings.member_auto_id = tbl_members.member_id WHERE tbl_members.member_id = ?';
-- To execute the code we have to convert it to a prepared statement
-- named stmt here, because it's what most people use in this instance
PREPARE stmt FROM #query;
-- Execute the statement using our input variable
EXECUTE stmt USING #input1;
-- Delete the prepared statement now we've run it.
DEALLOCATE PREPARE stmt;
-- Store our #vars back into the named vars.
SET fn_field_name_1 = #output1;
SET fn_field_name_2 = #output2;
SET fn_amount_for_profile_visible = #output3;