如果mysql中的条件无法按预期工作

Question

I am having two columns which are of integer types so I want to select the row if one of them have any data except "NULL" or "0".

cola     colb    colc    cold
NULL       12     plo     123
12         0      hou     NULL
0          0      plo      0
0          0      hou      123
NULL       13     hou      231
NULL       0      plo      NULL

So i want to select only 1,2,5 records so basically i have to select if colc is plo then any one of cola or colb should have value and if colc is hou then cold should have value.

I have written a query but its not giving proper result

I am giving my where condition where

IF ( cold = 'plo', cold, colc) IS NOT NULL 
AND IF ( cold = 'plo', cold, colc) <> '' 
AND ( ( (IF (colc <> 'plo', cola, colc) IS NOT NULL) 
    AND (IF (colc <> 'plo', cola, colc) <> '' )) 
       OR ( (IF (colc <> 'plo', colb, colc) IS NOT NULL) 
          AND (IF (colc <> 'plo', colb, colc) <> '' )) ) 

this is my where condition but after applying this also i am getting results which have both columns as 0 and colc as 'plo'

Is there something wrong in the where clause

Answer 1

The predicates look way more complicated than they need to be.

I'm not sure what the value of colc has to do with checking if cola or colb contains a non-zero integer value.

This would suffice:

   WHERE ( t.cola OR t.colb )

If you have some condition you want to check on colc , where that's not equal to 'plo' or 'plot'

   WHERE ( t.cola OR t.colb )
     AND t.colc NOT IN ('plo','plot')

---

There are other expressions which are more complicated and more ANSI-compliant which will achieve an equivalent result.

FOLLOWUP

Assuming the (unfortunately named) columns cola , colb and colc are integer types (or numeric types), you can do something like this:

  WHERE (t.colc = 'plo' AND (t.cola OR t.colb))
     OR (t.colc = 'hou' AND t.cold) 

The question was edited to clarify the specification... query should return rows that meet either of the following conditions:

• if colc is 'plo' then any one of cola or colb should have value other than 0 or NULL

• if colc is 'hou' then cold should have value other than 0 or NULL

Let's unpack the WHERE clause a little bit.

We like to use parens around all of the boolean AND / OR expressions. This makes the order of precedence explicit. This should help the reader who doesn't know/doesn't remember whether AND or OR has a higher precedence; using parens, even where they aren't strictly necessary, just removes some possible ambiguity, and makes our intent more clear.

In a boolean context, an integer value evaluates to either NULL, FALSE, or TRUE

• if the value of the expression is NULL, the boolean evaluation returns NULL.
• if the value of the expression is 0 (zero), it evaluates to boolean FALSE
• if the value of the expression is other than NULL or 0, it evaluates to boolean TRUE

The SQL three-valued boolean logic, expression (a OR b) evaluates to TRUE if either a or b evaluates to TRUE.

  OR    TRUE   FALSE  NULL
 -----  -----  -----  -----
 TRUE   TRUE   TRUE   TRUE 
 FALSE  TRUE   -      -
 NULL   TRUE   -      - 

With the AND operator, the expression (a AND b) evaluates to TRUE only of both a and b evaluate to TRUE.

rewrite

This same WHERE clause:

  WHERE (t.colc = 'plo' AND (t.cola OR t.colb))
     OR (t.colc = 'hou' AND t.cold) 

could be re-written to slightly more verbose:

  WHERE (t.colc = 'plo' AND ((t.cola<>0) OR (t.colb<>0)))
     OR (t.colc = 'hou' AND t.cold<>0)

or we could re-write that to be more convoluted, but it's not really necessary to do that... it would just make it harder to decipher.

Answer 2

NOT(((cola IS NULL) OR (cola=0)) AND ((colb IS NULL) OR (colb=0))) AND colc<>'plo'

让你2,4 - 约COLC是巴解组织在您的定义不是钻头，而是在代码