????5????????????????????????

????-->??????м??????????????????????????????????????????????????????????????й????

????-->?????

SELECT name
FROM   emp
WHERE  empno = 1234;

SELECT name
FROM   dept
WHERE  deptno = 10;

SELECT name
FROM   cat
WHERE  cat_type = 'RD';

????-->?????

SELECT e.name?? d.name?? c.name
FROM   cat c
     ?? dpt d
     ?? emp e
     ?? dual x
WHERE      NVL( 'X'?? x.dummy ) = NVL( 'X'?? e.ROWID(+) )
       AND NVL( 'X'?? x.dummy ) = NVL( 'X'?? d.ROWID(+) )
       AND NVL( 'X'?? x.dummy ) = NVL( 'X'?? c.ROWID(+) )
       AND e.emp_no(+) = 1234
       AND d.dept_no(+) = 10
       AND c.cat_type(+) = 'RD';

????-->???????SQL??????????????????????????????????????????????????????????????????

????6?? ?????????

????-->??????rowid????????????????????Ч

DELETE FROM emp e
WHERE  e.ROWID > (SELECT MIN( x.ROWID )
                  FROM   emp x
                  WHERE  x.empno = e.empno);

????7?????truncate ???? delete

????-->???????￡????????????????????ι????????????????????rollback??.????δ?????????????rollback???Oracle??????

????-->???SQL??????????????delete????????????insert?????insert??????????delete????update????????????delete??insert

????-->???truncate???????????DDL???????????κλ?????????????????????λ??.???????????Ч.???????rollback????????á?

????8???????????COMMIT??COMMIT????????????????

????-->???п??????????о????????COMMIT???????????????????????????????COMMIT???????????????

????-->COMMIT???????????

????-->1.?????????????????????

????-->2.????????????????е???

????-->3.???redo log buffer??????commit??redo log buffer?е?entries д??????????????????

????-->4.ORACLE?????????3??????е????????

????9?? ??????????

????-->????????￡?count??*????count??1?????.???????????????????????????е???????????????????????????????COUNT??EMPNO??

????-->???????????????????????????????????

????10?? ??Where????滻HAVING???

????-->??????????having??????HAVING ??????????????м???????????????й?????????????????????????

????-->???WHERE?????????????????????????????????????????????

????-->??Ч??

SELECT deptno?? AVG( sal )
FROM   emp
GROUP BY deptno
HAVING deptno = 20;

scott@CNMMBO> SELECT deptno?? AVG( sal )
  2  FROM   emp
  3  GROUP BY deptno
  4  HAVING deptno= 20;

Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          7  consistent gets
          0  physical reads
          0  redo size
        583  bytes sent via SQL*Net to client
        492  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed