Sql scripting sorcerypresentation

SQL Scripting Sorcery

RMOUG Training Days 2002Denver, CO

Overview

• Basic Concepts• Inline Query• DECODE• CASE• Stupid SQL Tricks• Special Surprise

Row Source

• Access Path• Result Set• ROWNUM pseudocolumn

– Order in result set, before explicit sorting– After predicate is applied

• ‘WHERE’ clause

Row Source

• All data is retrieved from a row source• May be a base object or the result set from a

previous operation• Oracle will use no more than 2 row sources

for any single operation• Result set may be row source for other

operations

Access Paths

• What is an access path• How access paths affect result sets• Using different access paths

Access Paths

EMP PK_EMPNO

How Access Paths Affect Result Sets

• Table– Physical Order in datafile(s)– ROWID order

• Index– ‘Sorted’ order– Even if table is accessed

• Other– Order of result set

Using Different Access Paths

• Using/Suppressing an Index• Hints• Join Order

Result Sets

• The output of an operation• Records are processed as a group

Sorting the Result Set

• Explicit Sorting– ORDER BY

• Implicit Sorting– DISTINCT– GROUP BY– UNION/INTERSECT/MINUS

Inline Query

• What is an Inline Query?• Hierarchical Query Joins• Top N Queries• Sampling

What is an Inline Query?

• FROM clause contains a ‘SELECT’ statement instead of a table or view– New in 7.2

• Cannot contain ORDER BY– Now Allowed in 8i

• Predicate cannot be dependent upon external condition– Cannot be a correlated subquery

Inline Query

select e2.ename2,

e2.empno2

from (select ename ename2,

empno empno2

from emp) e2;

Hierarchical Query Joins

• Basic Hierarchical Query uses one and only one table

• Join cannot occur in Hierarchical Query• Push query to inline query…it becomes just

another result set!

Base Hierarchical QuerySELECT level,

LPAD(' ',2*level-2)||emp.ename ename,

emp.empno,

emp.mgr,

emp.deptno

FROM emp

CONNECT BY PRIOR emp.empno = emp.mgr

START WITH emp.mgr is null;

LEVEL ENAME EMPNO MGR DEPTNO

---------- --------------- ---------- ---------- ----------

1 KING 7839 10

2 JONES 7566 7839 20

3 SCOTT 7788 7566 20

4 ADAMS 7876 7788 20

3 FORD 7902 7566 20

2 BLAKE 7698 7839 30

3 ALLEN 7499 7698 30

Joining a Hierarchical Query

SELECT level,


emp.empno,

emp.mgr,

dept.dname

FROM emp, dept

where emp.deptno = dept.deptno


START WITH emp.mgr is null;

FROM emp, dept

*

ERROR at line 2:

ORA-01437: cannot have join with CONNECT BY

Joining A Hierarchical Queryselect e.e_level,

e.ename,

e.empno,

e.mgr,

d.dname

from dept d,

(SELECT level e_level,


emp.empno empno,

emp.mgr mgr,

emp.deptno deptno

FROM emp


START WITH emp.mgr is null) e

where e.deptno = d.deptno;

Joining A Hierarchical Query

E_LEVEL ENAME EMPNO MGR DNAME

------- -------------- ---------- ---------- --------------

1 KING 7839 ACCOUNTING

2 CLARK 7782 7839 ACCOUNTING

3 MILLER 7934 7782 ACCOUNTING

2 JONES 7566 7839 RESEARCH

3 SCOTT 7788 7566 RESEARCH

4 ADAMS 7876 7788 RESEARCH

3 FORD 7902 7566 RESEARCH

Top N Queries

• What are the Top N values?• Rownum and result set are key• New features introduced in Oracle8i

– ORDER BY in inline query

Top N Values

• Limited number of records based upon a value or set of values– Top 2 salaries in the company– Top 2 salaries in each department– What happens in the case of a tie?

• Implemented in other platforms

Top 2 Salaries

Oracle 8.0.6select ename,

empno,

sal,

deptno,

hiredate

from (select distinct 0-sal,

ename,

empno,

sal,

deptno,

hiredate

from emp)

where rownum <= 2;

Oracle 8.1.6select *

from (select ename,

empno,

sal,

deptno,

hiredate

from emp

order by sal desc)

where rownum <= 2;

Top 2 Salaries

ENAME EMPNO SAL DEPTNO HIREDATE

---------- ---------- ---------- ---------- -----------

KING 7839 5000 10 17-NOV-1981

SCOTT 7788 3000 20 09-DEC-1982

• Only 2 records returned• ….but there are 2 employees with $3000

salary• Should 3 records be returned?

Top 2 Salaries, part 2


empno,

sal,

deptno,

hiredate

from emp

where sal >=

(select min(i_sal)

from (select

distinct 0-sal r_sal,

sal i_sal

from emp)

where rownum <= 2);


empno,

sal,

deptno,

hiredate

from emp

where sal >=

(select min(i_sal)

from

(select sal i_sal

from emp

order by i_sal desc)

where rownum <= 2);

Top 2 Salaries

ENAME EMPNO SAL DEPTNO HIREDATE

---------- ---------- ---------- ---------- -----------

KING 7839 5000 10 17-NOV-1981

FORD 7902 3000 20 03-DEC-1981

SCOTT 7788 3000 20 09-DEC-1982

• 3 records are returned• ….for the top 2 salaries• Is this the correct result?

Top 2 Salaries per Department

• Extraction of data is dependent upon data within query

• Move inline query into correlated subquery

Top 2 Salaries per Departmentselect m.ename,

m.sal,

m.deptno

from emp m

where m.sal >=

(select distinct o.sal

from emp o

where (o.sal,2) in

(select i.sal,

rownum

from (select

distinct 0-i2.sal r_sal,

i2.deptno,

i2.sal,

i2.rowid

from emp i2) i

where i.deptno = m.deptno))

order by deptno, sal desc;

select m.ename,

m.sal,

m.deptno

from emp m

where m.sal >=

(select distinct o.sal

from emp o

where (o.sal,2) in

(select i.sal,

rownum

from (select

i2.deptno,

i2.sal

from emp i2

order by i2.sal desc,

i2.deptno) i

where i.deptno = m.deptno))

order by deptno, sal desc;

Top 2 Salaries per Department

ENAME SAL DEPTNO

---------- ---------- ----------

KING 5000 10

CLARK 2450 10

SCOTT 3000 20

FORD 3000 20

BLAKE 2850 30

ALLEN 1600 30

TURNER 1600 30

RANK

• Added in Oracle8i– Added for analytical functions

• Will include ties, but will skip ranks• Can this be used for Top N Queries?

RANK

SELECT deptno, ename, sal, comm,

RANK() OVER (PARTITION BY deptno

ORDER BY sal DESC, comm) as rk

FROM emp

where RANK() OVER (PARTITION BY deptno

ORDER BY sal DESC, comm) <= 2;

where RANK() OVER (PARTITION BY deptno ORDER BY salDESC, comm) <= 2

*

ERROR at line 4:

ORA-30483: window functions are not allowed here

RANKselect *

from (SELECT deptno, ename, sal, comm,

RANK() OVER (PARTITION BY deptno

ORDER BY sal DESC, comm) as rk

FROM emp )

where rk <=2;

DEPTNO ENAME SAL COMM RK

---------- ---------- ---------- ---------- ----------

10 KING 5000 1

10 CLARK 2450 2

20 JONES 3000 1

20 FORD 3000 1

30 BLAKE 3000 1

30 ALLEN 1600 300 2

DECODE

• Deconstructing DECODE• Cross-tab reporting• Conditional DML• Simple menu• Duplicating a CASE function

Deconstructing Decode

• DECODE is a crude decision-making construct

• Implement– IF-THEN-ELSE– CASE

• Comparison must be equality– One or more values

Deconstructing DecodeSELECT ename,

deptno,

DECODE(deptno,

10, ‘ACCOUNTING’,

20, ‘RESEARCH’,

30, ‘SALES’,

‘NOT INDICATED’)

FROM emp;

IF DEPTNO = 10THEN ‘ACCOUNTING’ELSE IF DEPTNO = 20THEN ‘RESEARCH’ELSE IF DEPTNO = 30

THEN ‘SALES’ELSE ‘NOT INDICATED’

ENAME DEPTNO DECODE(DEPTNO

--------- ---------- -------------

TURNER 30 SALES

ALLEN 30 SALES

WARD 30 SALES

ADAMS 20 RESEARCH

JONES 20 RESEARCH

MARTIN 30 SALES

CLARK 10 ACCOUNTING

Cross-Tab Reports

• Spreadsheet type report– Down and Across– Static– Summary

• Each column is processed multiple times– ‘Ignore’ values not required

• GROUP BY important

Cross-Tab ReportsSELECT deptno DEPTNO,

SUM(DECODE(to_char(hiredate, 'YYYY'),

'1980', SAL+(NVL(COMM,0)),

0)) YR_1980,


'1981', SAL+(NVL(COMM,0)),

0)) YR_1981,


'1982', SAL+(NVL(COMM,0)),

0)) YR_1982,


'1983', SAL+(NVL(COMM,0)),

0)) YR_1983

FROM EMP

GROUP BY deptno;

DEPTNO YR_1980 YR_1981 YR_1982 YR_1983

---------- ---------- ---------- ---------- ----------

10 0 7450 1300 0

20 800 5975 3000 1100

30 0 11600 0 0

Conditional DML Dynamic Select

• Select different column based on dynamic values

• Same table, different columns• Different table, different columns

– Traditional – UNION– Cool – OUTER JOIN and DECODE

Conditional DML Dynamic Select

select s.segment_name,

s.segment_type,

decode(s.segment_type,

'INDEX', i.last_analyzed,

'TABLE', t.last_analyzed) analyze_date

from user_segments s,

user_tables t,

user_indexes i

where s.segment_name = t.table_name (+)

and s.segment_name = i.index_name (+);

SEGMENT_NAME SEGMENT_TYPE ANALYZE_DATE

------------------------------ ----------------- ------------

DEPT TABLE 06-DEC-2000

EMP TABLE 06-DEC-2000

IX_DEPTNO INDEX 06-DEC-2000

IX_DNAME INDEX 06-DEC-2000

IX_ENAME INDEX 06-DEC-2000

Conditional DMLDynamic Update

• Updating records based on dynamic value• Multiple update statements?• Single DECODE statement

– Use GREATEST and LEAST to simulate Range Check


select ename,

hiredate,

greatest(hiredate, to_date('01-APR-1981')) gt_date,

least(hiredate, to_date('01-APR-1982')) lt_date,

decode(greatest(hiredate, to_date('01-APR-1981')),

least(hiredate, to_date('01-APR-1982')), .1,

.05) pay_raise

from emp;

ENAME HIREDATE GT_DATE LT_DATE PAY_RAISE

---------- ----------- ----------- ----------- ----------

ALLEN 20-FEB-1981 01-APR-1981 20-FEB-1981 .05

WARD 22-FEB-1981 01-APR-1981 22-FEB-1981 .05

JONES 02-APR-1981 02-APR-1981 02-APR-1981 .1

FORD 03-DEC-1981 03-DEC-1981 03-DEC-1981 .1

MILLER 23-JAN-1982 23-JAN-1982 23-JAN-1982 .1

SCOTT 09-DEC-1982 09-DEC-1982 01-APR-1982 .05

ADAMS 12-JAN-1983 12-JAN-1983 01-APR-1982 .05


• Use CASE instead– But we haven’t learned that yet!

• Available Oracle 8.1.6• Much Cleaner Code


select ename,hiredate,

CASE when TRUNC(hiredate)between ’01-APR-1981’

and ’31-MAR-1982’

then 0.1else

then 0.05END pay_raise

from emp;

CASE

• Finally, a real CASE function!• New in Oracle8i

– ANSI-standard• Limit of 128 comparisons• Nonequality comparisons

CASE

DECODE ApproachSELECT ename,

deptno,

DECODE(deptno,

10, ‘ACCOUNTING’,

20, ‘RESEARCH’,

30, ‘SALES’,

‘NOT INDICATED’)

FROM emp;

CASE ApproachSELECT ename,

deptno,

CASE WHEN deptno = 10

THEN 'ACCOUNTING'

WHEN deptno = 20

THEN 'RESEARCH'

WHEN deptno = 30

THEN 'SALES'

ELSE 'NOT INDICATED'

END

FROM emp;

CASE

• Comparisons– Any Valid Oracle Expression – Do not have to be equality

Decode Approach

select ename,

sal,

decode(sign(sal-1000),

-1, 'Low Pay',


-1, 'Medium Pay',


-1, 'High Pay',

'DBA Pay')))pay_scale

from emp

Case Approach

select ename,

sal,

CASE when sal between 0 and 999

then 'Low Pay'

when sal between 1000 and 2500

then 'Medium Pay'

when sal between 2500 and 4000

then 'High Pay'

when sal > 4001

then 'DBA Pay'

END compensation

from emp

CASE

• May be nestedselect job,

comm,

sal,

CASE when comm is not null

then (CASE when comm > 100

then sal + comm

when comm <= 100

then sal + 100

END)

when job = 'CLERK'

then sal

else sal * 1.1

END compensation

from emp

Abandon Hope All Ye Who Enter Here

I’m Not Kidding…You Aren’t Ready For What

Comes Next!

No Looking Ahead…Turn Back NOW!

Column Level Selects

• Can you use a select statement in the column list or expression?

Using SELECT as an Expression

• What values can be returned from a column?– Data– Literal– Result of an Expression– Result of a SELECT statement

Basic Construct

select (select count(*)

from emp) emp_count

from dual;

EMP_COUNT

----------

8

Basic Construct

select (select count(*)

from emp) emp_count,

(select count(*)

from dept) dept_count

from dual;

EMP_COUNT DEPT_COUNT

---------- -----------

8 4

Basic Construct

• Subquery can return one and only one row• Subquery can return one and only one

column– Multiple columns may be concatenated

• The main query will return as many rows as there are in the main table

Basic Construct

• Can– restrict using a WHERE– use a GROUP BY– restrict using a HAVING– join multiple tables– be a correlated subquery

Selecting Multiple Values

select (select dname||loc

from dept

where deptno = 10)dname_loc

from dual;

DNAME_LOC

---------------------------

ACCOUNTINGNEW YORK

Joining Tables

select (select count(e1.empno)

from emp e1,

dept d1

where d1.loc = 'NEW YORK'

and d1.deptno = e1.deptno)

ny_emps

from dual

Using as an expression


s.segment_type,

decode(s.segment_type,

'TABLE', (select t.last_analyzed

from user_tables t

where t.table_name = s.segment_name),

'INDEX', (select i.last_analyzed

from user_indexes i

where i.index_name = s.segment_name),

NULL) date_analyzed

from user_segments s

Using as an expression


s.segment_type,

case when s.segment_type = 'TABLE'

then (select t.last_analyzed

from user_tables t

where t.table_name = s.segment_name)

when s.segment_type = 'INDEX'

then (select i.last_analyzed

from user_indexes i

where i.index_name = s.segment_name)

else NULL

end date_analyzed

from user_segments s

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Sql scripting sorcerypresentation