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1. SQL SCRIPTING SORCERY OR
USING SQL AND SQL*PLUS TO GO BEYOND “SELECT * FROM EMP;”
Daniel W. Fink
How do I show the manager-employee relationship with the department name
instead of number?
How do I see the top two salaries in the company?
How do I see the top two salaries in each department?
How do I select a sample of a production database to create a test database?
How do I select a sample from each department to create a test database?
How do I report with a Hire Year axis and Department axis format?
How do I give different raises if someone was hired between April 1, 1981 and
April 1 1982 or was hired at another time?
How do I select fields from different tables based upon data?
How can I avoid a self-join?
How can I create an interactive menu in SQL*Plus?
How can I default an accepted field to today’s date?
Can I use a select statement inside a decode?
Creativity is the key. Look upon the limits of SQL as a floor to build upon,
not a ceiling to stop progress.
SQL is the language used for all communication with Oracle databases. It is a very simple language with a limited number of
elements, but can be very powerful with a little creativity. Some of the limitations is that are cannot perform IF-THEN-ELSE
or LOOP logic. With a little ‘outside the box’ thinking, this logic can be partially duplicated. For any desired result set, there
are usually two or more sql statements that can achieve the desired result. One may be elegant, but a poor performer, while
the other may be complicated and convoluted, but a real speed demon. Which is better? That is for you to decide.
The first topic to be covered is the use of Inline Queries, or selects within a select. Some of the main uses for inline queries
are for Top N, joined-hierarchical, sampling and view-avoidance. The ubiquitous DECODE command will be covered next.
We will explore using DECODE for creating matrix reports, making range-of-value decisions and selecting different columns
from different tables.
Remember, WHAT you ask for and WHAT you receive are NOT always the same!
Warning – The topics covered here are examples of creative problem solving and may not be the optimal solution for
performance. In fact, they may cause your query to slow to a crawl. Always test the solutions on a nonproduction platform
and consider other avenues, such as PL/SQL or risk incurring the wrath of the DBA. All scripts were run against Oracle
8.0.6 on Solaris and Oracle 8.1.6 on Windows NT.
Basic Concepts
Row Source
All data is retrieved from a row source. This may be a base object, such as a table or index, or it may be a result set returned
from a previous operation. Oracle will use no more than 2 row sources at any one time. If a query accesses many objects,
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2. SQL Scripting Sorcery Fink
only 2 row sources are used at any time. The result set from this operation becomes one of the row sources for the next
operation.
Result Set
A result set is the output of an operation. According to relational theory, records are processed in groups, not as atomic units.
If two or more tables are joined, there may be intermediate result sets built during the execution of the statement.
Access Paths
Each time data is retrieved from the database, an access path is used. This may be a full-table scan, by rowid using an index
or by an index scan. The use of a particular access path may be determined by the Oracle optimizer or by using hints.
Rownum
Each row that is retrieved from the database that matches the WHERE condition is placed in a result set. The sequence within
the result set is the value in the pseudocolumn ROWNUM. If Oracle is using a full-table scan, the first row of the first block
is the first in the result set and is assigned ROWNUM 1. If Oracle uses an index to access the data, the first entry in the index
is assigned ROWNUM 1. Once a complete result set is built, the ORDER BY clause is applied. The result may be that the
order of the result set and the order presented to the user are not the same. If ROWNUM is used, the numbers may be and, in
fact, usually are, out of sequence.
ROWNUM and PREDICATES (the WHERE clause)
ROWNUM can be used to restrict the amount of data returned by a query, as we will see shortly. ROWNUM is assigned for
each row that matches all of the applicable conditions in the PREDICATE. For example, ROWNUM is assigned to a row
only if it matches the deptno condition. One common mistake is trying to use ROWNUM to find values greater than 1.
ROWNUM conditions can only be equal to 1 or less than/less than or equal to a number other than 1. The following
statement will never return a row.
select ename from emp where rownum = 2;
When the first row is read from the emp table, the PREDICATE is applied. Since this is the first row, it is conditionally
assigned ROWNUM of 1. However, the condition is that ROWNUM must be equal to 2. Since this condition is not met, the
row is not placed in the result set. The second row is read. Since the result set is empty, this row is assigned ROWNUM of 1.
Once again, the condition is not met and the row is not placed in the result set. This process repeats until all the rows are read.
However, the condition never evaluates to TRUE, so no rows are placed in the result set.
Hierarchical Query
A hierarchical query is a query representing the recursive relationship of a table. They are also called explosion-of-parts, tree,
organizational queries. The main requirement is that a column in the table has an optional relationship to another column. In
the EMP table, the MGR column is related to the EMPNO column.
What is an Inline Query?
An inline query is a subquery used in the place of a table or view in the FROM clause of a statement. It is also referred to as
an inline view, dynamic query or nested query. It was added in Oracle7.2. This can be used anywhere the FROM clause is
used, even in a correlated subquery. The inline query will create a result set that the parent query uses as a row source.
select col1, col2
from
(select colA col1, colB col2
from table1 Inline Query Parent Query
where colA = ‘TRUE’)
order by col1;
One of the challenges is to return a result set in ordered fashion without using the ORDER BY clause. ROWNUM is an
Oracle pseudocolumn that represents the order in which the row was retrieved from the database. It is assigned after any
conditions are applied in the WHERE or HAVING clause, but before the ORDER BY clause is applied. However, the use of
an index may cause the result set to be ordered before ROWNUM is assigned. In Oracle8i, the ability to use the ORDER BY
clause to the inline query was added. In prior releases, it was necessary to use access paths or other methods, such as
DISTINCT or GROUP BY, to return an ordered result set. If there are indexes available to satisfy the sorting criteria, hints
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can be used inside the inline query. Additionally, in order to reverse the sort order to descending, the sort key must be
manipulated.
One maintenance consideration is that an application must be rewritten if the underlying objects have a significant change.
Because the query is not stored in the data dictionary, dependencies cannot be determined by querying the
USER_DEPENDENCIES view.
An inline query is evaluated once per execution of the parent query. It can also be used to reduce network traffic. One
example was a view that accessed data across a dblink. By rewriting the view to access the remote data via an inline query,
performance was significantly improved. The subquery was executed once and returned one result set across the network,
instead of being executed once for each row in the preceding result set.
The output of an inline query is a static result set. In other words, it does not change based upon values presented in the
parent query. This is very important to remember and a key differentiation between an inline query and a correlated subquery.
? How do I show the manager-employee relationship with the department name
instead of number?
At first glance, this appears to be a fairly straightforward request. The basic query is very simple. It is adding in the
Department Name that adds a complication. In the EMP table, only the department number (deptno) is kept. This adheres to
the rules of relational design. However, to most users, 10 is not as meaningful as ACCOUNTING, the description of the
department (dname) in the DEPT table.
Simple hierarchical query
SELECT 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
3 WARD 7521 7698 30
3 MARTIN 7654 7698 30
3 TURNER 7844 7698 30
3 JAMES 7900 7698 30
2 CLARK 7782 7839 10
3 MILLER 7934 7782 10
Joined hierarchical Query
To retrieve the department name, we need to join the DEPT and EMP table. The relationship between them is the DEPTNO
column. A simple addition of the DNAME column, DEPT table and the join condition should return the department name
instead of department number.
SELECT level,
LPAD(' ',2*level-2)||emp.ename ename,
emp.empno,
emp.mgr,
dept.dname
FROM Emp, Dept
where emp.deptno = dept.deptno
CONNECT BY PRIOR emp.empno = emp.mgr
START WITH emp.mgr is null;
FROM Emp, Dept
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*
ERROR at line 2:
ORA-01437: cannot have join with CONNECT BY
Unfortunately, a join within a hierarchical query is not allowed. In order to get around this restriction, we place the
hierarchical query within an inline query and the problem is solved. The hierarchical query must be placed as the inline
query.
Joined hierarchical query using an inline view
select e.e_level,
e.ename,
e.empno,
e.mgr,
d.dname
from dept d,
(SELECT level e_level,
LPAD(' ',2*level-2)||emp.ename ename,
emp.empno empno,
emp.mgr mgr,
emp.deptno deptno
FROM Emp
CONNECT BY PRIOR emp.empno = emp.mgr
START WITH emp.mgr is null) e
where e.deptno = d.deptno;
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
2 BLAKE 7698 7839 SALES
3 ALLEN 7499 7698 SALES
3 WARD 7521 7698 SALES
3 MARTIN 7654 7698 SALES
3 TURNER 7844 7698 SALES
3 JAMES 7900 7698 SALES
How about adding the manager’s Name? We simply join with the emp table to get the manager name. It is important to
remember to use an outer join, otherwise KING is not returned because the record has no MGR relationship.
select e.ename, e.empno, e.mgr, e2.ename, d.dname
from dept d,
(SELECT rownum e_rownum,
LPAD(' ',2*level-2)||emp.ename ename,
emp.empno empno,
emp.mgr mgr,
emp.deptno deptno
FROM Emp
CONNECT BY PRIOR emp.empno = emp.mgr
START WITH emp.mgr is null) e,
emp e2
where e.deptno = d.deptno
and e2.empno (+) = e.mgr
order by e.e_rownum;
ENAME EMPNO MGR ENAME DNAME
------------------- ---------- ---------- -------------------- --------------
KING 7839 ACCOUNTING
JONES 7566 7839 KING RESEARCH
SCOTT 7788 7566 JONES RESEARCH
ADAMS 7876 7788 SCOTT RESEARCH
FORD 7902 7566 JONES RESEARCH
SMITH 7369 7902 FORD RESEARCH
CLARK 7782 7839 KING ACCOUNTING
MILLER 7934 7782 CLARK ACCOUNTING
BLAKE 7698 7839 KING SALES
TURNER 7844 7698 BLAKE SALES
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ALLEN 7499 7698 BLAKE SALES
WARD 7521 7698 BLAKE SALES
MARTIN 7654 7698 BLAKE SALES
JAMES 7900 7698 BLAKE SALES
Top N Queries
A Top N query is used to show the top values within a database. For example, a sales department may want to see the top 5
Customers by Revenue. One of the limitations in versions of Oracle prior to 8.1.5 was the inability to perform a Top N type
query. Other commercial databases had this functionality, for example, Microsoft Access Top Values and Sybase SET
ROWCOUNT. In order to simulate this behavior, we use inline queries to create an ordered result set. This type of query is
enhanced in Oracle 8.1.6 using the ORDER BY clause in the inline query.
The default sorting order for Oracle is ascending, from least to greatest. In the case of numbers, it is the smallest to largest. If
I use the default ordering scheme for salary, the lowest paid employees would be at the beginning of the result set. In pre-
Oracle 8.1.5 versions, I must find a method to reverse the sort order. I accomplished this by subtracting the salary from 0.
This results in a the larger salary being placed at the front of the result set. In later versions, I simply sort in descending order.
? How do I see the top two salaries in the company?
The key in this solution is to create a sorted result set and use it to find the lowest salary that meets the qualification. It seems
that it would be straightforward to use ROWNUM to find the 2nd salary and make a direct comparison. However, it is
important to remember that ROWNUM = 2 is not a condition that ever evaluates to TRUE.
In order to force a descending sort on the result set, I sorted on the negative value of the salary. This caused the largest salary
to be listed first in the result set.
Oracle 8.0.6
SELECT ename,
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);
Oracle 8.1.6
SELECT ename,
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);
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
Each query returns the exact same result set. The ORDER BY clause in 8i makes the 2nd query more understandable and
supportable.
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? How do I see the top two salaries in each department?
Now here is a bit of a puzzler. The top 2 salaries in the company was pretty straightforward. How could I select just the
department? Instead of using an inline query as the row source for the parent query, it was used as the row source for a
correlated subquery. Remember, the inline query can be used in any FROM clause, even in a nested correlated subquery!
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 DISTINCT 0-I2.SAL R_SAL,
I2.DEPTNO,
I2.SAL,
I2.ROWID
FROM EMP I2) I
WHERE I.DEPTNO = M.DEPTNO))
ORDER BY 3, 2 DESC;
ENAME SAL DEPTNO
---------- ---------- ----------
KING 5000 10
CLARK 2450 10
SCOTT 3000 20
FORD 3000 20
BLAKE 2850 30
ALLEN 1600 30
Now let’s update TURNER to create duplicate salaries in department 30 and rerun the query.
ENAME SAL DEPTNO
---------- ---------- ----------
KING 5000 10
CLARK 2450 10
SCOTT 3000 20
FORD 3000 20
BLAKE 2850 30
ALLEN 1600 30
TURNER 1600 30
Note that department 30 returns 3 records because the 2nd salary has two matching values. In essence, Allen and Turner have
‘tied’ for second place. How can this be resolved? You could use rownum to restrict further, but you may not return the same
employee each time.
? How do I select a sample of a production database to create a test database?
For testing purposes, it is often requested to retrieve a subset of the data. Until Oracle8I and the ability to export a subset of
the data, the process to manually extract data was difficult. Once you are able to select a sample, the next step of actually
extracting and transfering the data becomes much easier. The condition using MOD function on the ROWNUM in the inline
query will evaluate to TRUE for every 3rd record. To extract every 4th record, replace the 3 with a 4. It is just that simple.
SELECT ENAME,
EMPNO,
SAL ,
I_ROWNUM,
ROWNUM
FROM (SELECT ENAME,
EMPNO,
SAL,
ROWNUM I_ROWNUM
FROM EMP)
WHERE MOD(I_ROWNUM,3) = 0
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ENAME EMPNO SAL I_ROWNUM ROWNUM
---------- ---------- ---------- ---------- ----------
WARD 7521 1250 3 1
MARTIN 7654 1250 6 2
SMITH 7369 800 9 3
BLAKE 7698 2850 12 4
Oracle 8.1.6
SELECT ENAME,
EMPNO,
SAL,
ROWNUM
FROM EMP SAMPLE (33);
This query should return 33% (4 or 5 depending upon sampling algorithm) of the rows in the EMP table, but instead returned
between 1 and 7 rows each time it was executed. There is no explanation for this sampling variance. There are significant
restrictions in using the sample clause. Joins and remote tables are not supported and the cost-based optimizer will always be
used. In this case, I found that the pre-Oracle8i usage of mod on rownum was more reliable.
? How do I select a sample from each department to create a test database?
Once again, we use an inline view within the correlated subquery to restrict our result set.
SELECT ENAME P_ENAME,
DEPTNO P_DEPTNO
FROM EMP P
WHERE (P.ROWID,1) IN (SELECT I.ROWID I_ROWID,
MOD(ROWNUM,3)
FROM EMP I
WHERE I.DEPTNO = P.DEPTNO)
ORDER BY P_DEPTNO;
P_ENAME P_DEPTNO
---------- ----------
CLARK 10
ADAMS 20
SMITH 20
TURNER 30
MARTIN 30
Decode
What is a DECODE?
A simple method to implement if-then-else logic. The construct closely resembles the case statement used in several
languages. It can only do equality comparison. May be abused and create “ugly SQL”. It may not always be the most elegant
solution. DECODE provides an opportunity to be very creative, but it can also create performance and maintenance
nightmares. One thing to remember is that each row is processed, but each column can be processed multiple times.
IF-THEN-ELSE
DECODE (expression, if true1, then1, if true2, then2…else thenn)
SELECT ename,
deptno,
DECODE(deptno,
10, ‘ACCOUNTING’,
20, ‘RESEARCH’,
30, ‘SALES’,
‘NOT INDICATED’)
FROM emp;
ENAME DEPTNO DECODE(DEPTNO
---------- ---------- -------------
TURNER 30 SALES
ALLEN 30 SALES
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WARD 30 SALES
ADAMS 20 RESEARCH
JONES 20 RESEARCH
MARTIN 30 SALES
CLARK 10 ACCOUNTING
SCOTT 20 RESEARCH
SMITH 20 RESEARCH
KING 10 ACCOUNTING
JAMES 30 SALES
BLAKE 30 SALES
FORD 20 RESEARCH
MILLER 10 ACCOUNTING
? How do I report with a Hire Year axis and Department axis format?
One common request is to implement a Matrix (or Down and Across) report. The main challenge is to know the number of
columns that are required. The rows can be flexible, but the columns are fixed.
SELECT TO_CHAR(HIREDATE, 'YYYY') HIRE_YEAR ,
SUM(DECODE(DEPTNO,
10, SAL+(NVL(COMM,0)),
0)) DEPT_10,
SUM(DECODE(DEPTNO,
20, SAL+(NVL(COMM,0)),
0)) DEPT_20,
SUM(DECODE(DEPTNO,
30, SAL+(NVL(COMM,0)),
0)) DEPT_30
FROM EMP
GROUP BY TO_CHAR(HIREDATE, 'YYYY');
HIRE DEPT_10 DEPT_20 DEPT_30
---- ---------- ---------- ----------
1980 0 800 0
1981 7450 5975 11600
1982 1300 3000 0
1983 0 1100 0
To switch the axis so that the Years are listed across the top and Departments are listed down the side.
SELECT deptno DEPTNO,
SUM(DECODE(to_char(hiredate, 'YYYY'),
'1980', SAL+(NVL(COMM,0)),
0)) YR_1980,
SUM(DECODE(to_char(hiredate, 'YYYY'),
'1981', SAL+(NVL(COMM,0)),
0)) YR_1981,
SUM(DECODE(to_char(hiredate, 'YYYY'),
'1982', SAL+(NVL(COMM,0)),
0)) YR_1982,
SUM(DECODE(to_char(hiredate, 'YYYY'),
'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
? Changes based upon a range of values using GREATEST and LEAST
GREATEST will return the greatest value in a range of values
LEAST will return the least value in the range of values
The format is greatest (n, min_of_range), least(n, max_of_range)
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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
BLAKE 01-MAY-1981 01-MAY-1981 01-MAY-1981 .1
CLARK 09-JUN-1981 09-JUN-1981 09-JUN-1981 .1
TURNER 08-SEP-1981 08-SEP-1981 08-SEP-1981 .1
MARTIN 28-SEP-1981 28-SEP-1981 28-SEP-1981 .1
KING 17-NOV-1981 17-NOV-1981 17-NOV-1981 .1
JAMES 03-DEC-1981 03-DEC-1981 03-DEC-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
Let’s examine the first record for ALLEN. The decode expression evaluates to ‘01-APR-1981’. The first comparison
expression evaluates to ‘20-FEB-1981’. Is ‘01-APR-1981’ = ‘20-FEB-1981’? No, therefore the result is not used. There is
not another comparison, so the default value is used.
Let’s examine the record for Jones. The decode expression evaluates to ‘02-APR-1981’. The first comparison expression
evaluates to ‘02-APR-1981’. Is ‘01-APR-1981’ = ‘02-APR-1981’? Yes, therefore the result is used.
Let’s examine the first record for ADAMS. The decode expression evaluates to ‘12-JAN-1983’. The first comparison
expression evaluates to ‘01-APR-1982’. Is ‘12-JAN-1983’ = ‘01-APR-1982’? No, therefore the result is not used. There is
not another comparison, so the default value is used.
? How do I select fields from different tables based upon data?
What if you need to select similar data from different tables. The traditional approach is to perform a union. Using the
USER_ views, we extract information about TABLE and INDEX segments. In this case, the USER_SEGMENTS view is
accessed twice.
SELECT S.SEGMENT_NAME, 'TABLE' SEGMENT_TYPE, T.LAST_ANALYZED
FROM USER_SEGMENTS S,
USER_TABLES T
WHERE S.SEGMENT_NAME = T.TABLE_NAME
UNION
SELECT S.SEGMENT_NAME, 'INDEX' SEGMENT_TYPE, T.LAST_ANALYZED
FROM USER_SEGMENTS S,
USER_INDEXES T
WHERE S.SEGMENT_NAME = T.INDEX_NAME
ORDER BY 1;
SEGMENT_NAME SEGMENT_TYPE ANALYZE_DATE
------------------------------ ----------------- ------------
BONUS TABLE 06-DEC-2000
DEPT TABLE 06-DEC-2000
DUMMY TABLE
EMP TABLE 06-DEC-2000
EMP_2 TABLE
IX_DEPTNO INDEX 06-DEC-2000
IX_DNAME INDEX 06-DEC-2000
IX_ENAME INDEX 06-DEC-2000
SALGRADE TABLE 06-DEC-2000
The less traditional approach is to perform a union. By using a DECODE with an outer join, the same result set is returned. In
this case, the USER_SEGMENTS view is accessed only once.
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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
------------------------------ ----------------- ------------
BONUS TABLE 06-DEC-2000
DEPT TABLE 06-DEC-2000
DUMMY TABLE
EMP TABLE 06-DEC-2000
EMP_2 TABLE
IX_DEPTNO INDEX 06-DEC-2000
IX_DNAME INDEX 06-DEC-2000
IX_ENAME INDEX 06-DEC-2000
SALGRADE TABLE 06-DEC-2000
? How can I avoid a self-join?
One of the common DBA scripts is to look at hit ratios using the V$SYSSTAT view.
Is more efficient with small data sets (less than 1 million records).
SELECT (1 - SUM(DECODE(name, 'physical reads', value,0)) /
(SUM(DECODE(name, 'db block gets', value,0)) +
(SUM(DECODE(name, 'consistent gets', value,0))))) * 100
"Read Hit Ratio"
FROM v$sysstat;
Read Hit Ratio
--------------
99.780491
SELECT (1 - a.value/(b.value + c.value)) * 100 "Read Hit Ratio"
FROM v$sysstat a, v$sysstat b, v$sysstat c
WHERE a.name = 'physical reads'
AND b.name = 'db block gets'
AND c.name = 'consistent gets';
Read Hit Ratio
--------------
99.7805272
? How can I create an interactive menu in SQL*Plus?
sql_menu.sql
set verify off pages 0 feed off
accept table_choice prompt 'Enter Table (EMP/DEPT/SALGRADE/EXIT): '
set termout off
spool run_script.sql
select decode(UPPER('&table_choice'),
'EMP', '@select_emp',
'DEPT', '@select_dept',
'SALGRADE', '@select_salgrade',
'EXIT', '@exit_sqlplus',
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'@select_error') script_choice
from dual;
spool off
@run_script.sql
select_dept.sql
set termout on
select * from dept;
@sql_menu
select_emp.sql
set termout on
select * from emp;
@sql_menu
select_error.sql
select 'Invalid Menu Choice'
from dual;
@sql_menu
select_salgrade.sql
set termout on
select * from salgrade;
@sql_menu
exit_sqlplus.sql
exit
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