SQL Fundamentals SQL列字段的处理 SQL（casedecode行转列）

Posted 2020-09-29

 

列字段的处理 SQL Case   对列做处理 SQL> select deptno,sum(sal) from emp group by deptno;   Select case when deptno=10 then ‘ACCOUNTING‘ when deptno=20 then ‘RESERCH‘ when deptno=30 then ‘SALES‘ end, sum(sal) from emp group by deptno

列字段的处理 SQL Decode   还有一种情况是当什么都不是的情况下，用一个值代替 前言 DECODE()函数，它将输入数值与函数中的参数列表相比较，根据输入值返回一个对应值。函数的参数列表是由若干数值及其对应结果值组成的若干序偶形式。当然，如果未能与任何一个实参序偶匹配成功，则函数也有默认的返回值。 语法结构如下： decode (expression, search_1, result_1) decode (expression, search_1, result_1, search_2, result_2) decode (expression, search_1, result_1, search_2, result_2, ...., search_n, result_n) decode (expression, search_1, result_1, default) decode (expression, search_1, result_1, search_2, result_2, default) decode (expression, search_1, result_1, search_2, result_2, ...., search_n, result_n, default) 比较表达式和搜索字，如果匹配，返回结果；如果不匹配，返回default值；如果未定义default值，则返回空值。 select decode(deptno, 10, ‘ACCOUNTING‘, 20, ‘RESERCH‘, 30, ‘SALES‘ ), sum(sal) from emp group by deptno

行转列 SQL> select job,ename,sal from emp where job=‘MANAGER‘;   JOB       ENAME             SAL --------- ---------- ---------- MANAGER   JONES            2975 MANAGER   BLAKE            2850 MANAGER   CLARK            2450   SQL>   SQL> select job,decode(ename,‘BLAKE‘,SAL) BLAKE,decode(ename,‘JONES‘,SAL) JONES,decode(ename,‘CLARK‘,SAL) CLARK from emp where job=‘MANAGER‘;   JOB            BLAKE      JONES      CLARK --------- ---------- ---------- ---------- MANAGER                    2975 MANAGER         2850 MANAGER                               2450   SQL> select job,sum(decode(ename,‘BLAKE‘,SAL)) BLAKE,sum(decode(ename,‘JONES‘,SAL)) JONES,sum(decode(ename,‘CLARK‘,SAL)) CLARK from emp where job=‘MANAGER‘ group by job;   JOB            BLAKE      JONES      CLARK --------- ---------- ---------- ---------- MANAGER         2850       2975       2450   SQL> select job,avg(decode(ename,‘BLAKE‘,SAL)) BLAKE,max(decode(ename,‘JONES‘,SAL)) JONES,min(decode(ename,‘CLARK‘,SAL)) CLARK from emp where job=‘MANAGER‘ group by job;   JOB            BLAKE      JONES      CLARK --------- ---------- ---------- ---------- MANAGER         2850       2975       2450