工作中一些简单但是有用的SQL

1.删除一个表中重复的记录，只留一条记录。

DELETE FROM fcm_phonenum E WHERE E.ROWID > (SELECT MIN(X.ROWID)

FROM fcm_phonenum X

WHERE X.phonenum = E.phonenum);

2.给一个表做备份：

create table fcm_phonenum_bak as select * from fcm_phonenum;

3.合并列，使其输出内容也合并。

SELECT first_name || ' ' || last_name AS "Customer Name"

FROM customers

4.如何查找重复记录

SELECT *

FROM   TABLE_NAME

WHERE  ROWID!=(SELECT MAX(ROWID)

        FROM   TABLE_NAME D

        WHERE  TABLE_NAME.COL1=D.COL1

        AND    TABLE_NAME.COL2=D.COL2)

5.如何修改表名

ALTER TABLE OLD_TABLE_NAME RENAME TO NEW_TABLE_NAME;

6.获得全年日期

SELECT TO_CHAR(TO_DATE('20120101', 'YYYYMMDD')+ROWNUM-1, 'YYYY-MM-DD') AS YEAR_DATE

FROM   ALL_OBJECTS

WHERE  ROWNUM <= TO_CHAR(TO_DATE('20121231', 'YYYYMMDD'), 'DDD')

7.修改字段信息

ALTER TABLE TABLE_NAME MODIFY (FIELD_NAME VARCHAR2(100));

8.字符串的连接

(1)SELECT CONCAT(COL1,COL2) FROM TABLE_NAME;(2) SELECT COL1 || COL2 FROM TABLE_NAME;