MySQL IF Statements in Query issues - mysql

Question

I have the following query that I am trying to execute. It is the starting point for a query required to run a report:
SET #fname = 'Bob';
SET #blah = 0;
SELECT CASE WHEN #fname IS NULL THEN #blah = 1 ELSE #blah END;
IF (#blah > 0) THEN
SELECT * FROM mytable
END IF;
Something is apparently wrong with my syntax but I cannot figure it out. I've written other queries using IF statements without issue. This will not run in either SQLyog or Workbench. It says there is a sytax error on "IF" with or without the parens, doesn't matter.
All I need is the ability to evaluate a variable/input parameter in the IF statement.
Any help is appreciated. NOTE - the SELECT CASE may not be necessary if I can get the IF to evaluate parameters properly but I was trying any possible solutions.
Thanks

Answer 1

You can use IF-THEN construction only inside BEGIN...END clause, which can be used only in procedures, functions, triggers, and events. It is impossible to use it in a simple script.
For your case I'd suggest this one -
SELECT * FROM mytable WHERE #blah > 0;

Answer 2

There needs to be a procedure or some form of script that needs to be executed given the case.
CALL procedure method needs to be initiated in the report datasource in such scenarios
Script can be written in following way: (Note: PROCEDURE can have parameters as required)
DELIMITER ?
CREATE PROCEDURE XYZ()
BEGIN
SET #fname = 'Bob';
SET #blah = 1;
SELECT CASE WHEN #fname IS NULL THEN #blah = 0 ELSE #blah END;
IF (#blah > 0) THEN
SELECT * from mytable;
END IF;
END ?
DELIMITER;
You can then pass the CALL XYZ() with or without parameters as required to your datasource or where you would pass your query to be executed for generating report.
Following works properly on MySQL Workbench. SELECT CASE query can be removed from the above procedure if not required.

Answer 3

I see issue with else statement:
SELECT CASE WHEN #fname IS NULL THEN #blah = 1 END;

Answer 4

// Using procedure getting result as per requirement
drop procedure abc;
DELIMITER //
create procedure abc()
begin
declare fname varchar(10);
declare blah int;
set fname = 'Bob';
set blah = 0;
if(fname IS not NULL) then
SELECT * from studmaster;
end if;
end //
DELIMITER ;
//--comment--> for execute procedure
call abc();

Answer 5

Not sure if this helps you much, but you can use if statement in an sql query
Select Blah.name,sum(Blah.quan) as SumofQuan, IF(Blah.descr LIKE '%searchterm%', "FOUND", IF(Blah.descr ="x", "x", "The Rest")) as New_DECRIPTION

Answer 6

I understand more of SQL SERVER, then it may be that my answer is not very helpful, but anyway here is my help:
Try changing the code snippet below,
SELECT #blah = (CASE WHEN #fname IS NULL THEN 1 ELSE #blah END)

Answer 7

In my view when using Sql server i found that the variable cannot assigned a value without declaring it..
I think you must have done as:
declare #fname nvarchar(50)
declare #blah int
then you must assign value to the variabl..
SET #fname = 'Bob'
SET #blah = 0
SELECT CASE WHEN #fname IS NULL THEN #blah = 1 ELSE #blah END;
IF (#blah > 0) THEN
SELECT * FROM mytable
END IF;