Question

CREATE TABLE table1(kid char(2),color varchar(9));

INSERT INTO table1('k1'.'yello');
INSERT INTO table1('k1'.'red');
INSERT INTO table1('k2'.'yello');
INSERT INTO table1('k2'.'blue');
INSERT INTO table1('k3'.'yello');

问：显示table1的kid，其color值为黄色和红色（两者都有）？

什么是sql查询？

Answer 1

使用：

  SELECT t.kid
    FROM TABLE1 t
   WHERE t.color IN ('yellow', 'red')
GROUP BY t.kid
  HAVING COUNT(DISTINCT t.color) = 2

IN子句只会获取color值为黄色或红色的记录
GROUP BY是删除重复项所必需的
COUNT(DISTINCT t.color) = 2可确保返回有效的kid值。如果没有DISTINCT，则两个黄色/等将满足COUNT检查

Answer 2

SELECT kid 
  FROM table1 as t, 
       table1 as t2 
 WHERE t1.color = 'yellow' 
   AND t1.kid = t2.kid 
   AND t2.color = 'red'

什么是下表的sql查询？

2 个答案: