MYSQL列转行-CFANZ编程社区

建表语句：

1 2 3 4 5 6 7 8 9	`CREATE` `TABLE` `tb_score1(` `id` `INT(11)` `NOT` `NULL` `auto_increment,` `userid` `VARCHAR(20)` `NOT` `NULL` `COMMENT` `'用户id',` `cn_score` `DOUBLE` `COMMENT` `'语文成绩',` `math_score` `DOUBLE` `COMMENT` `'数学成绩',` `en_score` `DOUBLE` `COMMENT` `'英语成绩',` `po_score` `DOUBLE` `COMMENT` `'政治成绩',` `PRIMARY` `KEY(id)` `)ENGINE = INNODB` `DEFAULT` `CHARSET = utf8;`

插入数据：

1 2 3	`INSERT` `INTO` `tb_score1(userid,cn_score,math_score,en_score,po_score)` `VALUES` `('001',90,92,80,0);` `INSERT` `INTO` `tb_score1(userid,cn_score,math_score,en_score,po_score)` `VALUES` `('002',88,90,75.5,0);` `INSERT` `INTO` `tb_score1(userid,cn_score,math_score,en_score,po_score)` `VALUES` `('003',70,85,90,82);`

查询数据表中的内容（即转换前的结果）

1	`SELECT` `*` `FROM` `tb_score1`

MYSQL列转行_mysql

转换后：

MYSQL列转行_#include_02

本质是将userid的每个科目分数分散成一条记录显示出来。

直接上SQL：

1 2 3 4 5 6 7 8	`SELECT` `userid,'语文'` `AS` `course,cn_score` `AS` `score` `FROM` `tb_score1` `UNION` `ALL` `SELECT` `userid,'数学'` `AS` `course,math_score` `AS` `score` `FROM` `tb_score1` `UNION` `ALL` `SELECT` `userid,'英语'` `AS` `course,en_score` `AS` `score` `FROM` `tb_score1` `UNION` `ALL` `SELECT` `userid,'政治'` `AS` `course,po_score` `AS` `score` `FROM` `tb_score1` `ORDER` `BY` `userid`

这里将每个userid对应的多个科目的成绩查出来，通过UNION ALL将结果集加起来，达到上图的效果。

/*
* The task state array is a strange "bitmap" of
* reasons to sleep. Thus "running" is zero, and
* you can test for combinations of others with
* simple bit tests.
*/
static const char * const task_state_array[] = {
"R (running)", /* 0 */
"S (sleeping)", /* 1 */
"D (disk sleep)", /* 2 */
"T (stopped)", /* 4 */
"t (tracing stop)", /* 8 */
"X (dead)", /* 16 */
"Z (zombie)", /* 32 */
};
  1 #include<stdio.h>
  2 #include<unistd.h>
  3 #include<stdlib.h>
  4 int main()
  5 {
  6   pid_t id =fork();
  7   if(id==0)
  8   {
  9     int cnt=5;
 10     while(cnt)
 11     {
 12       printf("child,pid:%d,ppid:%d,cnt:%d\n",getpid(),getppid(),cnt);                                                                                                                        
 13         --cnt;
 14       sleep(1);
 15     }
 16     exit(0);
 17   }
 18   else
 19   {
 20     while(1)
 21     {
 22       printf("parent,pid:%d,ppid:%d\n",getpid(),getppid());
 23       sleep(1);
 24     }
 25   }
 26   return 0;
 27 }