SQL在多个表上选择EXIST作为布尔值（位）

Question

I am using the accepted answer from this question , but for multiple tables.

$result = mssql_query("SELECT CAST(
       CASE WHEN 
         EXISTS(select 1 from codes where code = '".$generatedCode."') OR 
         EXISTS(select 1 from pakete where code = '".$generatedCode."') OR
         EXISTS(select 1 from kunden where code = '".$generatedCode."') OR
         EXISTS(select 1 from formulare where code = '".$generatedCode."') OR  
         EXISTS(select 1 from berater where code = '".$generatedCode."') 
       THEN 1 
       ELSE 0 
       END 
    AS BIT) as 'exists'";

$row = mssql_fetch_assoc($result);
if ($row['exists']==0)

Theoretically it looks good, practically it works too. But it happens from time to time, that the query (i think) wents wrong and returns 1 even if there is a "code" in one of the tables.

Maybe someone knows a better solution for checking across tables, where it could happen that the searched varchar exists in one or two tables only.

fyi: generatedcode is a nine digit alphanumeric unique string.

Regards, Markus

UPDATE: The Query works as expected, the failure was a wrong named variable after return, so the original generatedcode (the duplicate one) was used instead. Thanks for your help and for simplifying the query.

Answer 1

You know, you can use simple union and num_rows, there's no need to select a bit - it won't do you any good unless your query is a part of other complex query:

$sql="select 1 from codes where code = '".$generatedCode."' 
union select 1 from pakete where code = '".$generatedCode."'
union select 1 from kunden where code = '".$generatedCode."'
union select 1 from formulare where code = '".$generatedCode."'
union select 1 from berater where code = '".$generatedCode."'";
$result = mssql_query($sql);
if(mssql_num_rows($result)){}

Answer 2

I am guessing that your code works. You can do a couple things to improve it. First, the cast() isn't necessary because you can put in bit literals directly (see here ). The following code uses both methods for expressing a bit literal.

Second, don't use single quotes for column names (and, of course, mysql_ is deprecated, but that is another matter because this just focuses on the query). In fact, you should avoid using reserved words as column names. So:

SELECT (CASE WHEN 
         EXISTS(select 1 from codes where code = '".$generatedCode."') OR 
         EXISTS(select 1 from pakete where code = '".$generatedCode."') OR
         EXISTS(select 1 from kunden where code = '".$generatedCode."') OR
         EXISTS(select 1 from formulare where code = '".$generatedCode."') OR  
         EXISTS(select 1 from berater where code = '".$generatedCode."') 
         THEN 0b1 
         ELSE  b'0' 
       END) as CodeExists

By the way, I would discourage you from using bits, unless you really know what you are doing in terms of optimization. They may not save space and they may not run faster. The following seems totally reasonable to me:

SELECT (EXISTS(select 1 from codes where code = '".$generatedCode."') OR 
        EXISTS(select 1 from pakete where code = '".$generatedCode."') OR
        EXISTS(select 1 from kunden where code = '".$generatedCode."') OR
        EXISTS(select 1 from formulare where code = '".$generatedCode."') OR  
        EXISTS(select 1 from berater where code = '".$generatedCode."') 
       ) as CodeExists