sql - How can I test an IF statement in MySQL? -

how can test if statement in mysql ?

i need know, happens when query if statement , returns nothing (0 row selected) ?

in other word, select query returns when no row selected? return null? if yes, throw error? if ( null ) ...? or in case statement of if won't execute?

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in reality, have code this:

if ( select banned users id=new.user_id )  // stuff 

note: banned column contains either 0 or 1.

all want know, code safe when query doesn't return row? mean throw error or nothing happens (just if statement doesn't execute) ?

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noted wanted test myselft, don't know how can test if statement in mysql. example, wanted test code:

begin     if ( select banned users id=new.user_id )         select 'test';     endif; end 

but code above doesn't run. that's why i've asked question.

an if statement can tested in context of mysql stored program (a procedure, function or trigger.) mysql doesn't support anonymous blocks.

to test if statement, can create procedure

delimiter $$  create procedure foo begin   if ( some_condition )      select 'evaluation of some_condition returned true' msg;   else      select 'evaluation of some_condition did not return true' msg;   end if; end$$      delimiter ;  call foo;