OPERATOR 中的多个 SQL 查询

Question

I tried to statements

SELECT s.*
FROM status s
WHERE s.reg IN (Select reg from sdel) OR
      s.reg IN (Select reg from ddel);

The above mentioned statement works out but when I tried the below mentioned statement, it didn't extract any results for me.

 SELECT s.*
    FROM status s
    WHERE s.reg IN (Select reg,pic from sdel where sdel.reg = status.reg) OR
          s.reg IN (Select reg,pic from ddel where ddel.reg = status.reg) OR
          s.reg IN (Select reg,pic from gdel where gdel.reg = status.reg) OR
          s.reg IN (Select reg,pic from ip where ip.reg = status.reg);

Answer 1

Do this with two in expressions:

SELECT s.*
FROM status s
WHERE s.reg IN (Select reg from sdel) OR
      s.reg IN (Select reg from ddel);

You can also use UNION ALL for one query. But two separate queries give more opportunity for optimization.

Answer 2

In your second query you extract both the attributes reg and pic and the compare with the only attribute reg , so the result is always false.

If you need to compare only reg , then remove pic from the internal select clause, like in:

$res=mysql_query("SELECT s.*
    FROM status s
    WHERE s.reg IN (Select reg from sdel where sdel.reg = status.reg) OR
          s.reg IN (Select reg from ddel where ddel.reg = status.reg) OR
          s.reg IN (Select reg from gdel where gdel.reg = status.reg) OR
          s.reg IN (Select reg from ip where ip.reg = status.reg);");