Useful Complex Queries in SQL

1. Ordering a result set with a column not in result set or queried tables

Order by a column that is not appear in SELECT clause:
--------------------------------------------------------
SELECT empno, ename, sal, deptno
FROM emp
ORDER BY hiredate;

Order by Expression:
----------------------
SELECT empno, ename, sal,deptno,'2' sortby
FROM emp
UNION 
SELECT empno, ename, sal,deptno,'1' sortby
FROM emp 
ORDER BY sortby;

Order by concatenated columns:
---------------------------------
SELECT first_name||' '||Last_name name, salary, deptno
FROM emp_details
order by name;

Order by column position:
---------------------------
SELECT empno, ename, sal, deptno
FROM emp
ORDER BY 1,2;

2. Find string which is not numeric:

SELECT DISTINCT SALES_ORDER FROM T_TEMPORARY_TABLE_30_6718

WHERE REGEXP_LIKE (SALES_ORDER, '[^[:digit:]]');

3.  Check previous row and make it null if same else new value will remain.

Input Record:

C1           C2           C3           C4           DT_PRV_DT

E1           P1           L1            BA1        4/1/2014

E1           P1           L2            BA1        4/2/2014

E1           P2           L2            BA1        4/3/2014

E1           P2           L2            BA2        4/4/2014

Query:

select * from TEST_DATA order by DT_PRV_DT;

select d.C1,

       decode(c2, prev_c2, null, c2) c2,

       decode(c3, prev_c3, null, c3) c3,

       decode(c4, prev_c4, null, c4) c4,

       DT_PRV_DT

  from (select C1,

               C2,

               LAG(c2) OVER(ORDER BY DT_PRV_DT) prev_c2,

               C3,

               LAG(c3) OVER(ORDER BY DT_PRV_DT) prev_c3,

               C4,

               LAG(c4) OVER(ORDER BY DT_PRV_DT) prev_c4,

               DT_PRV_DT

          from TEST_DATA) d

order by DT_PRV_DT;

Output:

C1           C2           C3           C4           DT_PRV_DT

E1           P1           L1            BA1        4/1/2014

E1                           L2                            4/2/2014

E1           P2                                           4/3/2014

E1                                           BA2        4/4/2014

4. Combine the data and get only the not NULL value for each field.

 Create table temp_shoeb (col1 varchar2(50),col2 varchar2(50),col3 varchar2(50),col4 varchar2(50),col_date date);

                COL1      COL2      COL3      COL4      COL_DATE

                val1                                        val4        2/13/2014

                val11      val22                                      2/6/2014

               val111                   val333   val444   2/18/2014

                select * from temp_shoeb order by col_date;

select *

  from (select LAST_VALUE(d.col1 IGNORE NULLS) OVER(ORDER BY d.col_dateROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS column1,

               LAST_VALUE(d.col2 IGNORE NULLS) OVER(ORDER BY d.col_dateROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS column2,

               LAST_VALUE(d.col3 IGNORE NULLS) OVER(ORDER BY d.col_dateROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS column3,

               LAST_VALUE(d.col4 IGNORE NULLS) OVER(ORDER BY d.col_dateROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS column4

          from (select * from temp_shoeb order by col_date) d)

where rownum = 1;

5. LEAD function to update values based on next column:

SELECT ri.RECORDID,

               ri.EMPLOYEE_ID, 

               ri.EFFECTIVE_FROM,

               NVL(LEAD (EFFECTIVE_FROM,1) OVER (PARTITION BY EMPLOYEE_ID ORDER BY EMPLOYEE_ID , EFFECTIVE_FROM ) -1, TO_DATE('12/31/9999','MM/DD/YYYY'))  AS next_eff_from

        FROM T_EMP_HISTORY ri 

        WHERE ri.RECORDID= 7007  

        ORDER BY ri.EMPLOYEE_ID,ri.EFFECTIVE_FROM, next_eff_from;

6. Returning values in update and insert statement

DECLARE

    id          number;

    first_name  varchar2(30);

    last_name   varchar2(30);

    start_date  varchar2(30);

    end_date    varchar2(30);

    salary      varchar2(30);

    city        varchar2(30);

    description varchar2(30);

 BEGIN

    UPDATE employee

       SET salary = salary + (salary * .025) , start_date=sysdate

     where id = 1 returning id, first_name, last_name, start_date, end_date,

     salary, city, description into id, first_name, last_name,

     start_date, end_date, salary, city, description;

    dbms_output.put_line(id || ' ' || first_name || ' ' || last_name || ' ' ||start_date || ' ' || end_date || ' ' || salary || ' ' || city || ' ' ||description);

  END;