# 800 Phone Puzzle

For a given 800 phone number (like 1-800-123-4567) find all number-letter representations.

• Use a single SELECT statement only.
• Only last 4 digits of the phone number have to be replaced with letters.
• Exactly 1 letter (out of 4) must be vowel,  the rest – consonant
• The following table shows all possible mappings:
Digit Maps to
1 1
2 A, B, C
3 D, E, F
4 G, H, I
5 J, K, L
6 M, N, O
7 P, Q, R, S
8 T, U, V
9 W, X, Y, Z
0 0

# Solutions:

Essentially, all solutions below share the same idea of generating the letter based phone numbers. The differences are in a way the mapping CTE is created and a way to limit the number of vowels to 1.

### Solution #1. Compact form of creating the map CTE with recursive check for the vowels:

WITH map AS (
SELECT digit, letter, '4357' phone
FROM TABLE(sys.odcivarchar2list('00','11','2ABC','3DEF','4GHI',
'5JKL','6MNO','7PQRS','8TUV','9WXYZ')) t,
LATERAL(SELECT SUBSTR(t.column_value,1,1) digit,
SUBSTR(t.column_value,1+LEVEL,1) letter
FROM dual
CONNECT BY SUBSTR(t.column_value,1+LEVEL,1) IS NOT NULL) x
), res(str, lvl, phone,has_vowel) AS (
SELECT letter, 1, phone,
CASE WHEN letter IN ('A','E','I','O','U') THEN 1 ELSE 0 END
FROM map
WHERE SUBSTR(phone,1,1)=TO_CHAR(map.digit)
UNION ALL
SELECT res.str || letter, res.lvl+1, res.phone,
CASE WHEN letter IN ('A','E','I','O','U')
OR res.has_vowel=1 THEN 1 ELSE 0 END
FROM res JOIN map ON SUBSTR(res.phone, res.lvl+1,1)=TO_CHAR(map.digit)
WHERE res.lvl+1<=LENGTH(res.phone)
AND NOT (letter IN ('A','E','I','O','U') AND res.has_vowel=1)
)
SELECT '1-800-123-' || str phone
FROM res
WHERE lvl=LENGTH(phone)
AND has_vowel=1

### Solution #2. Using more efficient way of creating the map CTE :

WITH x AS (
SELECT ROWNUM-1 digit,COLUMN_VALUE letters
FROM TABLE(sys.odcivarchar2list('0','1','ABC','DEF','GHI','JKL',
'MNO','PQRS','TUV','WXYZ'))
), map AS (
SELECT digit, SUBSTR(letters, level, 1) letter, '4357' phone
FROM x
CONNECT BY SUBSTR(letters, level, 1) IS NOT NULL
AND PRIOR digit = digit
AND PRIOR DBMS_RANDOM.VALUE IS NOT NULL
), res(str, lvl, phone,has_vowel) AS (
SELECT letter, 1, phone,
CASE WHEN letter IN ('A','E','I','O','U') THEN 1 ELSE 0 END
FROM map
WHERE SUBSTR(phone,1,1)=TO_CHAR(map.digit)
UNION ALL
SELECT res.str || letter, res.lvl+1, res.phone,
CASE WHEN letter IN ('A','E','I','O','U')
OR res.has_vowel=1 THEN 1 ELSE 0 END
FROM res JOIN map ON SUBSTR(res.phone, res.lvl+1,1)=TO_CHAR(map.digit)
WHERE res.lvl+1<=LENGTH(res.phone)
AND NOT (letter IN ('A','E','I','O','U') AND res.has_vowel=1)
)
SELECT '1-800-123-' || str phone
FROM res
WHERE lvl=LENGTH(phone)
AND has_vowel=1

### Solution #3. Much more efficient way of creating the map CTE and using Regular Expression to limit the vowels :

WITH d AS (
SELECT LEVEL+1 n, CASE WHEN LEVEL+1 IN (7,9) THEN 4 ELSE 3 END cnt,
'4357' phone
FROM dual
CONNECT BY LEVEL<=8
), a AS (
SELECT CHR(ASCII('A')+LEVEL-1) letter, ROWNUM rn
FROM dual
CONNECT BY CHR(ASCII('A')+LEVEL-1)<='Z'
), x AS (
SELECT n,
1+NVL(SUM(cnt) OVER(ORDER BY n ROWS BETWEEN UNBOUNDED PRECEDING
AND 1 PRECEDING),0) c1,
SUM(cnt) OVER(ORDER BY n) c2,
phone
FROM d
), map AS (
SELECT n digit, letter, x.phone
FROM x JOIN a ON a.rn BETWEEN x.c1 AND x.c2
UNION
SELECT ROWNUM-1, TO_CHAR(ROWNUM-1), x.phone
FROM x
WHERE ROWNUM<=2
), res(str, lvl) AS (
SELECT letter, 1
FROM map
WHERE SUBSTR(map.phone,1,1)=TO_CHAR(map.digit)
UNION ALL
SELECT res.str || letter, res.lvl+1
FROM res JOIN map ON SUBSTR(map.phone, res.lvl+1,1)=TO_CHAR(map.digit)
WHERE res.lvl+1<=LENGTH(map.phone)
AND REGEXP_COUNT(res.str || letter,'[AEIOU]')<=1
)
SELECT str phone
FROM res
WHERE lvl=4
AND REGEXP_COUNT(str,'[AEIOU]')=1

You can execute the above SQL statements in Oracle Live SQL environment.
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# Yet Another Top Employee Puzzle

Find the employee who remained the top paid employee (excluding the president) the longest period of time between 1980 and 1981

• Use a single SELECT statement only.
• President should be excluded from the analysis.
• Show the number of days the employee remained the top paid person as well as Start Date (hiredate) and End Date (the date when another top employee started)
• The End Date for the last top paid employee in the interval should be 31-DEC-1981.

Expected Result:

EMPNO ENAME JOB SAL Start Date End Date Days on Top
7566 JONES MANAGER 2975 02-APR-81 03-DEC-81 245

# Solutions:

### Solution #1. Using RANK to filter the top employee:

WITH x AS (
SELECT empno, ename, job, sal, hiredate,
MAX(sal)OVER(ORDER BY hiredate) max_sal
FROM scott.emp
WHERE job!='PRESIDENT'
), y AS (
SELECT empno, ename, job, sal, hiredate start_date, max_sal,
LEAD(hiredate) OVER(ORDER BY hiredate) end_date
FROM x
WHERE sal=max_sal
), z AS (
SELECT y.*, LEAST(end_date, date'1981-12-31')-start_date days_on_top,
RANK()OVER(ORDER BY LEAST(end_date, date'1981-12-31')-start_date DESC) rk
FROM y
WHERE EXTRACT(YEAR FROM start_date) IN (1980, 1981)
)
SELECT empno,ename,job,sal, start_date "Start Date",
end_date "End Date", days_on_top	"Days on Top"
FROM z
WHERE rk=1

### Solution #2. Using Subquery to filter the top employee:

WITH x AS (
SELECT empno, ename, job, sal, hiredate,
MAX(sal)OVER(ORDER BY hiredate) max_sal
FROM scott.emp
WHERE job!='PRESIDENT'
AND hiredate>=date'1980-01-01'
), y AS (
SELECT empno, ename, job, sal, hiredate start_date,
LEAST(date'1981-12-31',
LEAD(hiredate) OVER(ORDER BY hiredate)) end_date
FROM x
WHERE sal=max_sal
)
SELECT empno,ename,job,sal, start_date "Start Date",
end_date "End Date", end_date-start_date "Days on Top"
FROM y
WHERE end_date-start_date=(SELECT MAX(end_date-start_date) FROM y)

### Solution #3. Using MODEL with RETURN UPDATED ROWS to filter the top employee:

WITH e AS (
SELECT empno, ename, sal, job, LEAST(hiredate, date'1981-12-31') hiredate,
MAX(sal)OVER(ORDER BY hiredate) max_sal
FROM scott.emp
WHERE hiredate>=date'1980-01-01'
AND job!='PRESIDENT'
), x AS (
SELECT empno, ename, job, sal, hiredate,
date'1981-12-31')-hiredate diff,
date'1981-12-31') end_date
FROM e
WHERE sal=max_sal
)
SELECT empno, ename, job, sal, hiredate "Start Date",
end_date "End Date", diff "Days on Top"
FROM x
MODEL RETURN UPDATED ROWS
DIMENSION BY (empno, RANK()OVER(ORDER BY diff DESC) rk)
MEASURES(ename,job,sal, hiredate, end_date, diff, 0 dummy)
RULES(dummy[ANY, 1]=1)

The following query will only work as long as there is only 1 top paid employee who stayed on top the longest. In case if we had more than 1 it would only list one of those:

WITH x AS (
SELECT empno, ename, job, sal, hiredate,
MAX(sal)OVER(ORDER BY hiredate) max_sal
FROM scott.emp
WHERE job!='PRESIDENT'
), y AS (
SELECT empno, ename, job, sal, hiredate start_date,
LEAST(date'1981-12-31',
LEAD(hiredate) OVER(ORDER BY hiredate)) end_date,
LEAST(date'1981-12-31',
LEAD(hiredate) OVER(ORDER BY hiredate))-hiredate days_top
FROM x
WHERE sal=max_sal
ORDER BY days_top DESC NULLS LAST, hiredate
)
SELECT *
FROM y
WHERE ROWNUM=1

You can execute the above SQL statements in Oracle Live SQL environment.
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# Mimic ROW_NUMBER function

Write a single SELECT statement that produces the same result as the following one:

SELECT e.*, ROW_NUMBER()OVER(PARTITION BY deptno ORDER BY ename) rn
FROM scott.emp e
• Use a single SELECT statement only.
• Analytic functions are NOT allowed
• Any SQL clauses that use PARTITION BY keywords are NOT allowed

Expected Result:

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO RN
7782 CLARK MANAGER 7839 09-JUN-81 2450 10 1
7839 KING PRESIDENT 17-NOV-81 5000 10 2
7934 MILLER CLERK 7782 23-JAN-82 1300 10 3
7876 ADAMS CLERK 7788 23-MAY-87 1100 20 1
7902 FORD ANALYST 7566 03-DEC-81 3000 20 2
7566 JONES MANAGER 7839 02-APR-81 2975 20 3
7788 SCOTT ANALYST 7566 19-APR-87 3000 20 4
7369 SMITH CLERK 7902 17-DEC-80 800 20 5
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 1
7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 2
7900 JAMES CLERK 7698 03-DEC-81 950 30 3
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 4
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 5
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 6

# Solutions:

### Solution #1. Using MATCH_RECOGNIZE clause

Credit to: Naoto Katayama

SELECT empno,ename,job,mgr,hiredate,sal,comm,deptno,rn
FROM scott.emp
MATCH_RECOGNIZE (
ORDER BY deptno,ename,empno
MEASURES RUNNING COUNT(*) AS rn
ALL ROWS PER MATCH
PATTERN (FIRSTROW NEXTROWS*)
DEFINE
FIRSTROW AS PREV(FIRSTROW.deptno) IS NULL
OR PREV(FIRSTROW.deptno) != FIRSTROW.deptno,
NEXTROWS AS PREV(NEXTROWS.deptno) = NEXTROWS.deptno
)

### Solution #2. Using Self-Join with Cartesian Product and GROUP BY

Partial Credit to: Boobal Ganesan

SELECT e1.empno,e1.ename,e1.job,e1.mgr,e1.hiredate,e1.sal,e1.comm,e1.deptno,
COUNT(*) rn
FROM scott.emp e1 LEFT OUTER JOIN scott.emp e2
ON e1.deptno = e2.deptno
AND e2.ename || ROWIDTOCHAR(e2.ROWID) <= e1.ename || ROWIDTOCHAR(e1.ROWID)
GROUP BY e1.empno,e1.ename,e1.job,e1.mgr,e1.hiredate,e1.sal,e1.comm,e1.deptno
ORDER BY e1.deptno, COUNT(*)

### Solution #3. Using CTE, ROWNUM, and arithmetic formula

WITH x AS (
SELECT *
FROM scott.emp
ORDER BY deptno, ename
), y AS (
SELECT deptno, MIN(ROWNUM) min_rn
FROM x
GROUP BY deptno
)
SELECT x.*, ROWNUM-y.min_rn+1 AS rn
FROM x JOIN y ON x.deptno=y.deptno
ORDER BY x.deptno, x.ename

You can execute the above SQL statements in Oracle Live SQL environment.
My Oracle Group on Facebook:

If you like this post, you may want to join my new Oracle group on Facebook: https://www.facebook.com/groups/sqlpatterns/

Would you like to read about many more tricks and puzzles?

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## How to generate a list of first N binary numbers in Oracle SQL?

In my recent post I showed how to convert a decimal number (i.e. an integer) into a binary string. We can build upon that technique to answer the question:

WITH x AS (
SELECT LEVEL n
FROM dual
CONNECT BY LEVEL<=50
)
SELECT x.N, y.bin
FROM x, LATERAL (SELECT LISTAGG(SIGN(BITAND(x.N, POWER(2,LEVEL-1))),'')
WITHIN GROUP(ORDER BY LEVEL DESC) bin
FROM dual
CONNECT BY POWER(2, LEVEL-1)<=x.N) y

Note the LATERAL keyword (Oracle 12c new feature) that enables us to reference “x” in the inline view “y”. In pre-12c world, we would have to use TABLE/CAST/MULTISET function composition to achieve the same result:

WITH x AS (
SELECT LEVEL n
FROM dual
CONNECT BY LEVEL<=50
)
SELECT x.N, y.column_value bin
FROM x, TABLE(CAST(MULTISET(
SELECT LISTAGG(SIGN(BITAND(x.N, POWER(2,LEVEL-1))),'')
WITHIN GROUP(ORDER BY LEVEL DESC) bin
FROM dual
CONNECT BY POWER(2, LEVEL-1)<=x.N) AS sys.odcivarchar2list)) y

The idea used in the following query is based on a totally different approach. It builds a string of “0”s and “1”s in a loop until its length reaches a desired value:

WITH x(v, n) AS (
SELECT column_value, 1
FROM TABLE(sys.odcivarchar2list('0','1'))
UNION ALL
SELECT x.v || t.column_value, x.n+1
FROM TABLE(sys.odcivarchar2list('0','1')) t JOIN x on LENGTH(x.v)=n
WHERE n<=CEIL(LOG(2,50))
), y AS (
SELECT NVL(LTRIM(x.v,'0'),'0') bin, ROWNUM-1 dec
FROM x
WHERE n=(SELECT MAX(n) FROM x)
)
SELECT *
FROM y
WHERE dec<=50

To better understand the above query, try the following one:

SELECT *
FROM TABLE(sys.odcivarchar2list('0','1')),
TABLE(sys.odcivarchar2list('0','1')),
TABLE(sys.odcivarchar2list('0','1')),
TABLE(sys.odcivarchar2list('0','1'))

If we put enough tables in the Cartesian product and concatenate all column_value columns in a single character string expression, we will achieve our goal. The challenge with this approach is to dynamically change the number of the tables in the FROM clause. This can be simulated in the recursive WITH clause by repeatedly adding more and more collections of bits (0 and 1).

### My Oracle Group on Facebook:

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### Would you like to read about many more tricks and puzzles?

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## Puzzle of the Week #18:

There are gaps in values of empno column in emp table. The challenge is to find all the gaps within the range of employee numbers already in use. All numbers should be grouped in ranges (see expected result section below). A single SELECT statement against emp table is expected.

### Expected Result:

Avail. Emp Numbers
------------------
7370 - 7498
7500 - 7520
7522 - 7565
7567 - 7653
7655 - 7697
7699 - 7781
7783 - 7787
7789 - 7838
7840 - 7843
7845 - 7875
7877 - 7899
7901 - 7901
7903 - 7933

## Solutions

### #1: Using GROUP BY Over ROWNUM expression

WITH x AS (
SELECT MIN(empno) min_no, MAX(empno) max_no
FROM emp
), y AS (
SELECT min_no+LEVEL-1 empno
FROM x
CONNECT BY min_no+LEVEL-1<=max_no
MINUS
SELECT empno
FROM emp
)
SELECT MIN(empno) || ' - ' || MAX(empno) "Avail. Emp Numbers"
FROM y
GROUP BY empno-ROWNUM
ORDER BY empno-ROWNUM;

Avail. Emp Numbers
--------------------
7370 - 7498
7500 - 7520
7522 - 7565
7567 - 7653
7655 - 7697
7699 - 7781
7783 - 7787
7789 - 7838
7840 - 7843
7845 - 7875
7877 - 7899
7901 - 7901
7903 - 7933

### #2: Using MATCH_RECOGNIZE (Oracle 12c and up;  credit to Zohar Elkayam)

WITH x AS (
SELECT MIN(empno) min_no, MAX(empno) max_no
FROM emp
), y AS (
SELECT min_no+LEVEL-1 empno
FROM x
CONNECT BY min_no+LEVEL-1<=max_no
MINUS
SELECT empno
FROM emp
)
SELECT firstemp || ' - ' || lastemp "Avail. Emp Numbers"
FROM y
MATCH_RECOGNIZE (
ORDER BY empno
MEASURES
A.empno firstemp,
LAST(empno) lastemp
ONE ROW PER MATCH
AFTER MATCH SKIP PAST LAST ROW
PATTERN (A B*)
DEFINE B AS empno = PREV(empno)+1
);

### #3: Using LEAD Analytic function (credit to Krishna Jamal)

WITH x AS
(
SELECT empno, LEAD(empno,1) OVER(ORDER BY empno) lead_empno
FROM emp
)
SELECT (empno+1) || ' - ' || (lead_empno-1) "Avail. Emp Numbers"
FROM x

### My Oracle Group on Facebook:

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### Would you like to read about many more tricks and puzzles?

For more tricks and cool techniques check my book “Oracle SQL Tricks and Workarounds” for instructions.

## Puzzle of the Week #15:

Find all the year based intervals from 1975 up to now when the company did not hire employees. Use a single SELECT statement against emp table.

years
------------
1975 - 1979
1983 - 1986
1988 - 2016

## Solutions

### #1: Grouping by an expression on ROWNUM (no Analytic functions!)

SQL> col years for a15

SQL> WITH x AS (
2  SELECT 1975+LEVEL-1 yr
3  FROM dual
4  CONNECT BY 1975+LEVEL-1<=EXTRACT(YEAR FROM SYSDATE)
5  MINUS
6  SELECT EXTRACT(YEAR FROM hiredate)
7  FROM emp
8  )
9  SELECT MIN(yr) || ' - ' || MAX(yr) "years"
10  FROM x
11  GROUP BY yr-ROWNUM
12  ORDER BY yr-ROWNUM;

years
---------------
1975 - 1979
1983 - 1986
1988 - 2016

### #2: Calculating steps with Analytic function and grouping by a sum of step.

WITH x AS (
SELECT 1975+LEVEL-1 yr
FROM dual
CONNECT BY 1975+LEVEL-1<=EXTRACT(YEAR FROM SYSDATE)
MINUS
SELECT EXTRACT(YEAR FROM hiredate)
FROM emp
), y AS (
SELECT DECODE(yr, LAG(yr,1)OVER(ORDER BY yr)+1, 0, 1) AS step, yr
FROM x
), z AS (
SELECT yr, SUM(step)OVER(ORDER BY yr) grp
FROM y
)
SELECT MIN(yr) || ' - ' || MAX(yr) "years"
FROM z
GROUP BY grp
ORDER BY grp;

years
---------------
1975 - 1979
1983 - 1986
1988 - 2016

### #3: Using Self Outer Join to calculate steps

WITH x AS (
SELECT 1975+LEVEL-1 yr
FROM dual
CONNECT BY 1975+LEVEL-1<=EXTRACT(YEAR FROM SYSDATE)
MINUS
SELECT EXTRACT(YEAR FROM hiredate)
FROM emp
), y AS (
SELECT x1.yr, NVL2(x2.yr, 0, 1) step
FROM x x1 LEFT JOIN x x2 ON x1.yr=x2.yr+1
), z AS (
SELECT yr, SUM(step)OVER(ORDER BY yr) grp
FROM y
)
SELECT MIN(yr) || ' - ' || MAX(yr) "years"
FROM z
GROUP BY grp
ORDER BY grp;

years
---------------
1975 - 1979
1983 - 1986
1988 - 2016

### My Oracle Group on Facebook:

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### Would you like to read about many more tricks and puzzles?

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## Puzzle of the week #3 Solutions

Puzzle of the week #3Calendar Summary Report:

Write a single SELECT statement that outputs number of Sundays, Mondays, Tuesdays, etc in each month of the current year.

The output should look like this:

MONTH  SUN  MON  TUE  WED  THU  FRI  SAT
----- ---- ---- ---- ---- ---- ---- ----
JAN      5    4    4    4    4    5    5
FEB      4    5    4    4    4    4    4
MAR      4    4    5    5    5    4    4
APR      4    4    4    4    4    5    5
MAY      5    5    5    4    4    4    4
JUN      4    4    4    5    5    4    4
JUL      5    4    4    4    4    5    5
AUG      4    5    5    5    4    4    4
SEP      4    4    4    4    5    5    4
OCT      5    5    4    4    4    4    5
NOV      4    4    5    5    4    4    4
DEC      4    4    4    4    5    5    5

We suggest you to go over the post that explains how to generate various date ranges before checking the solutions below.

Solution #1: Using PIVOT simulation

WITH days AS (
SELECT TRUNC(SYSDATE,'YEAR')+ROWNUM-1 d
FROM dual
CONNECT BY TO_CHAR(TRUNC(SYSDATE,'YEAR')+ROWNUM-1, 'YYYY')=TO_CHAR(SYSDATE,'YYYY')
)
SELECT TO_CHAR(d,'MON') Month,
SUM(CASE WHEN TO_CHAR(d,'DY')='SUN' THEN 1 END) SUN,
SUM(CASE WHEN TO_CHAR(d,'DY')='MON' THEN 1 END) MON,
SUM(CASE WHEN TO_CHAR(d,'DY')='TUE' THEN 1 END) TUE,
SUM(CASE WHEN TO_CHAR(d,'DY')='WED' THEN 1 END) WED,
SUM(CASE WHEN TO_CHAR(d,'DY')='THU' THEN 1 END) THU,
SUM(CASE WHEN TO_CHAR(d,'DY')='FRI' THEN 1 END) FRI,
SUM(CASE WHEN TO_CHAR(d,'DY')='SAT' THEN 1 END) SAT
FROM days
GROUP BY TO_CHAR(d,'MON'), TO_CHAR(d,'MM')
ORDER BY TO_CHAR(d,'MM');

Solution #2: Using PIVOT

SELECT month, mon, sun, mon, tue, wed, thu, fri, sat
FROM
(
SELECT TO_CHAR(TRUNC(SYSDATE,'YEAR')+ROWNUM-1, 'MON') month,
TO_CHAR(TRUNC(SYSDATE,'YEAR')+ROWNUM-1, 'DY') dy,
TO_CHAR(TRUNC(SYSDATE,'YEAR')+ROWNUM-1, 'MM') mm
FROM dual
CONNECT BY TO_CHAR(TRUNC(SYSDATE,'YEAR')+ROWNUM-1, 'YYYY')=TO_CHAR(SYSDATE,'YYYY')
)
PIVOT
(
COUNT(dy)
FOR dy IN ('SUN' sun, 'MON' mon, 'TUE' tue, 'WED' wed, 'THU' thu, 'FRI' fri, 'SAT' sat)
)
ORDER BY mm;

Solution #3: Using PIVOT simulation and Recursive WITH

WITH days(d) AS
(
SELECT TRUNC(SYSDATE,'YEAR') d
FROM dual
UNION ALL
SELECT d+1
FROM days
WHERE TO_CHAR(d+1,'YYYY')=TO_CHAR(SYSDATE,'YYYY')
)
SELECT TO_CHAR(d,'MON') Month,
SUM(CASE WHEN TO_CHAR(d,'DY')='SUN' THEN 1 END) SUN,
SUM(CASE WHEN TO_CHAR(d,'DY')='MON' THEN 1 END) MON,
SUM(CASE WHEN TO_CHAR(d,'DY')='TUE' THEN 1 END) TUE,
SUM(CASE WHEN TO_CHAR(d,'DY')='WED' THEN 1 END) WED,
SUM(CASE WHEN TO_CHAR(d,'DY')='THU' THEN 1 END) THU,
SUM(CASE WHEN TO_CHAR(d,'DY')='FRI' THEN 1 END) FRI,
SUM(CASE WHEN TO_CHAR(d,'DY')='SAT' THEN 1 END) SAT
FROM days
GROUP BY TO_CHAR(d,'MON'), TO_CHAR(d,'MM')
ORDER BY TO_CHAR(d,'MM');

If you like this post, you may want to join my new Oracle group on Facebook: https://www.facebook.com/groups/sqlpatterns/

For more tricks and cool techniques check my book “Oracle SQL Tricks and Workarounds” for instructions.

## How to generate a random sample of numeric and alpha-numeric values

Puzzle: Generate a random sample of numeric and alpha-numeric values

This problem often arises when you need to run a test and you don’t have a table to experiment with. Not a problem any more!

Related Post: Use TRUNC function to generate various date ranges

Step 1: Generate a random list of 10 alpha-numeric values:

SELECT dbms_random.string('x',3) rnd
FROM dual
CONNECT BY ROWNUM<=10

RND
-----
3TI
1JB
CIP
9SE
79K
YNZ
VEG
V0B
KPN
ILR

Step 2: Generate a random list of 10 integer values:

SELECT TRUNC(dbms_random.VALUE(-999,999)) rnd
FROM dual
CONNECT BY ROWNUM<=10

RND
----
539
153
979
689
212
267
-5
-832
-160
665

Step 3: Mix the above lists together (with equal shares):

SELECT CASE WHEN MOD(level,2)=0 THEN dbms_random.string('x',3)
ELSE TO_CHAR(TRUNC(dbms_random.VALUE(-999,999)))
END rnd
FROM dual
CONNECT BY ROWNUM<=10

RND
-------
-513
SVA
-475
NRM
-903
G45
-654
2S3
415
0HG

Step 4: Let’s have a fairly random number of integers and strings in the output

WITH x AS (
SELECT CASE WHEN MOD(level,2)=0 THEN dbms_random.string('x',3)
ELSE TO_CHAR(TRUNC(dbms_random.VALUE(-999,999)))
END rnd,
ROW_NUMBER()OVER(ORDER BY dbms_random.value) rk
FROM dual
CONNECT BY ROWNUM<=40
)
SELECT CAST(rnd AS VARCHAR2(4)) rnd
FROM x
WHERE rk<=10

RND
----
-985
0TG
8JZ
-714
500
199
7IJ
249
RNI
F2G

Step 5: Final touch – let’s add a column that would flag integers

WITH x AS (
SELECT CASE WHEN MOD(level,2)=0 THEN dbms_random.string('x',3)
ELSE TO_CHAR(TRUNC(dbms_random.VALUE(-999,999)))
END rnd,
ROW_NUMBER()OVER(ORDER BY dbms_random.value) rk
FROM dual
CONNECT BY ROWNUM<=40
)
SELECT CAST(rnd AS VARCHAR2(4)) rnd, CASE WHEN REGEXP_LIKE(rnd,'^-?[[:digit:]]+\$') THEN 1 ELSE 0 END is_int
FROM x
WHERE rk<=10

RND      IS_INT
---- ----------
WIS           0
-558          1
0QR           0
-433          1
RB0           0
PT8           0
409           1
YOV           0
969           1
FFI           0

If you like this post, you may want to join my new Oracle group on Facebook: https://www.facebook.com/groups/sqlpatterns/

For more tricks and cool techniques check my book “Oracle SQL Tricks and Workarounds” for instructions.

## Use TRUNC function to generate various date ranges

How to use TRUNC function to generate a date range? As it will be demonstrated below, it is very straightforward and simple to grasp. Let’s start from the very beginning

Step 1. Generate Numeric Range

First, you need to understand how to generate a numeric range. Let say, you need to generate a range of integers from 1 to 10. There are 2-3 traditional ways to do it.

Method 1: Use Connect By clause:

SQL> SELECT LEVEL, ROWNUM
2  FROM dual
3  CONNECT BY LEVEL<=10;

LEVEL     ROWNUM
---------- ----------
1          1
2          2
3          3
4          4
5          5
6          6
7          7
8          8
9          9
10         10

Likewise, you can use ROWNUM in the CONNECT BY:

SQL> SELECT LEVEL, ROWNUM
2  FROM dual
3  CONNECT BY ROWNUM<=10;

LEVEL     ROWNUM
---------- ----------
1          1
2          2
3          3
4          4
5          5
6          6
7          7
8          8
9          9
10         10

Method 2: Using some data dictionary table that is always available:

SQL> SELECT ROWNUM
2  FROM all_objects
3  WHERE ROWNUM<=10;

ROWNUM
----------
1
2
3
4
5
6
7
8
9
10

If the table does not have enough rows, you can use a Cartesian Product (emp table only has 14 rows):

SQL> SELECT ROWNUM
2  FROM emp, emp
3  WHERE ROWNUM<=16;

ROWNUM
----------
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

The above method involves disk I/O which makes it fairly inefficient compare to the CONNECT BY method.

Method 3: Using Recursive WITH clause:

SQL> WITH x(rnum) AS (
2  SELECT 1 AS rnum
3  FROM dual
4  UNION ALL
5  SELECT rnum+1
6  FROM x
7  WHERE rnum

This method first became available in Oracle 11.2 when Oracle introduced support to the Recursive WITH clause. The good thing about this method is that it is often available in other RDBMS (SQL Server, Teradata, etc.) that don’t have a support for CONNECT BY.

Step 2. Convert the Numeric range from Step 1 into a Date Range.
This step is very simple since we know that we can easily add days to a specific date value. For simplicity, we will stick with CONNECT BY method of numeric range generation:

SQL> SELECT SYSDATE + LEVEL - 1 AS day
2  FROM dual
3  CONNECT BY LEVEL<=10;

DAY
---------
08-MAR-16
09-MAR-16
10-MAR-16
11-MAR-16
12-MAR-16
13-MAR-16
14-MAR-16
15-MAR-16
16-MAR-16
17-MAR-16

Now, we will want to generate very specific data ranges.

Problem: Generate the date range for current week from Sunday to Saturday.

All we need to know is how to get the first day of the week. We have explained this in details in a previous post:

SQL> SELECT TRUNC(SYSDATE, 'DAY') week_start
2  FROM dual;

WEEK_STAR
---------
06-MAR-16

Now, we will generate the range for the week knowing that the week has 7 days:

SQL> SELECT TRUNC(SYSDATE, 'DAY')+LEVEL-1 AS day
2  FROM dual
3  CONNECT BY LEVEL<=7;

DAY
---------
06-MAR-16
07-MAR-16
08-MAR-16
09-MAR-16
10-MAR-16
11-MAR-16
12-MAR-16

Do we really need to know how many days our desired date range has? The answer is NO. All we need is to ensure that every subsequent day remains in the same date interval (same week – in our case). How can we identify the week – by its first day!

SQL> SELECT TRUNC(SYSDATE, 'DAY')+LEVEL-1 AS day
2  FROM dual
3  CONNECT BY TRUNC(TRUNC(SYSDATE, 'DAY')+LEVEL-1, 'DAY')=TRUNC(SYSDATE, 'DAY')
4  /

DAY
---------
06-MAR-16
07-MAR-16
08-MAR-16
09-MAR-16
10-MAR-16
11-MAR-16
12-MAR-16

As long as subsequent day’s first day of the week remains the same as the current day’s first day of the week, we can continue the recursion!

Using this idea, generation of the month’s date range is even simpler as we can use either TRUNC function to get the first day of the month, or TO_CHAR(…, ‘MM’) – to extract the month:

SQL> SELECT TRUNC(SYSDATE, 'MON')+LEVEL-1 AS day
2  FROM dual
3  CONNECT BY TO_CHAR(TRUNC(SYSDATE, 'MON')+LEVEL-1, 'MM')=TO_CHAR(SYSDATE, 'MM')
4  /

DAY
---------
01-MAR-16
02-MAR-16
03-MAR-16
...
30-MAR-16
31-MAR-16

How about getting the date range for the current Quarter?

SQL> SELECT TRUNC(SYSDATE, 'Q')+LEVEL-1 AS day
2  FROM dual
3  CONNECT BY TO_CHAR(TRUNC(SYSDATE, 'Q')+LEVEL-1, 'Q')=TO_CHAR(SYSDATE, 'Q')
4  /

DAY
---------
01-JAN-16
02-JAN-16
03-JAN-16
...
30-MAR-16
31-MAR-16

A Year?

SQL> SELECT TRUNC(SYSDATE, 'YY')+LEVEL-1 AS day
2  FROM dual
3  CONNECT BY TO_CHAR(TRUNC(SYSDATE, 'YY')+LEVEL-1, 'YY')=TO_CHAR(SYSDATE, 'YY')
4  /

DAY
---------
01-JAN-16
02-JAN-16
03-JAN-16
...
30-DEC-16
31-DEC-16

As you can see, the solution is very simple!

If you like this post, you may want to join my new Oracle group on Facebook: https://www.facebook.com/groups/sqlpatterns/

For more tricks and cool techniques check my book “Oracle SQL Tricks and Workarounds” for instructions.

## Puzzle of the Week Challenge – Solutions to the 1st Puzzle

Last week we started a new contest, Puzzle of the Week. Today we publish correct answers for the 1st puzzle:

 Write a single SELECT statement that would output a calendar for the current month in a traditional tabular format (7 columns: Sun-Sat).

Solution #1: No Sub-query solution! We consider it the best solution.

To better understand the following query we suggest you to first check if you can understand Solution #3 (see below).

SELECT MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'),
'1', LEVEL)) SUN,
MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'),
'2', LEVEL)) MON,
MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'),
'3', LEVEL)) TUE,
MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'),
'4', LEVEL)) WED,
MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'),
'5', LEVEL)) THU,
MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'),
'6', LEVEL)) FRI,
MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'),
'7', LEVEL)) SAT
FROM DUAL
CONNECT BY LEVEL <= TO_CHAR(LAST_DAY(SYSDATE),'DD')
GROUP BY TRUNC(TRUNC(SYSDATE,'MON') + LEVEL-1, 'DAY')
ORDER BY TRUNC(TRUNC(SYSDATE,'MON') + LEVEL-1, 'DAY');

Solution #2: Using PIVOT

SELECT "'SUN'" SU,"'MON'" MO,"'TUE'" TU,"'WED'" WE,
"'THU'" TH,"'FRI'" FR,"'SAT'" SA
FROM
(
SELECT TRUNC(TRUNC(SYSDATE,'MON')+LEVEL-1,'DAY') WEEK_START,
TO_CHAR(TRUNC(SYSDATE,'MON')+LEVEL-1,'DD') DD,
TO_CHAR(TRUNC(SYSDATE,'MON')+LEVEL-1,'DY') DY
FROM DUAL
CONNECT BY TO_CHAR(TRUNC(SYSDATE,'MON')+LEVEL-1,'yyyymm')=
TO_CHAR(SYSDATE,'yyyymm')
)
PIVOT
(
MAX(DD)
FOR DY IN ('SUN','MON','TUE','WED','THU','FRI','SAT')
)
ORDER BY week_start;

Solution #3: Use the power of CONNECT BY clause to generate a range of days for the current month

WITH x AS (
SELECT TRUNC(SYSDATE, 'MON')+level-1 d
FROM DUAL
CONNECT BY MONTHS_BETWEEN(TRUNC(SYSDATE, 'MON')+level-1, TRUNC(SYSDATE, 'MON'))<1
)
SELECT MAX(CASE WHEN TO_CHAR(D,'DY')='SUN' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS SUN,
MAX(CASE WHEN TO_CHAR(D,'DY')='MON' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS MON,
MAX(CASE WHEN TO_CHAR(D,'DY')='TUE' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS TUE,
MAX(CASE WHEN TO_CHAR(D,'DY')='WED' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS WED,
MAX(CASE WHEN TO_CHAR(D,'DY')='THU' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS THU,
MAX(CASE WHEN TO_CHAR(D,'DY')='FRI' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS FRI,
MAX(CASE WHEN TO_CHAR(D,'DY')='SAT' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS SAT
FROM X
GROUP BY TRUNC(D, 'DAY')
ORDER BY TRUNC(D, 'DAY')

Solution #4: Use existing table(s) to generate a range of days for the current month

WITH X AS (
SELECT TRUNC(SYSDATE, 'MON')+ROWNUM-1 D
FROM emp,emp
WHERE TO_CHAR(TRUNC(SYSDATE, 'MON')+ROWNUM-1, 'YYYYMM')=TO_CHAR(SYSDATE, 'YYYYMM')
AND ROWNUM<=31
)
SELECT MAX(CASE WHEN TO_CHAR(D,'DY')='SUN' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS SUN,
MAX(CASE WHEN TO_CHAR(D,'DY')='MON' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS MON,
MAX(CASE WHEN TO_CHAR(D,'DY')='TUE' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS TUE,
MAX(CASE WHEN TO_CHAR(D,'DY')='WED' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS WED,
MAX(CASE WHEN TO_CHAR(D,'DY')='THU' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS THU,
MAX(CASE WHEN TO_CHAR(D,'DY')='FRI' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS FRI,
MAX(CASE WHEN TO_CHAR(D,'DY')='SAT' THEN TO_CHAR(D,'DD')
ELSE '  ' END) AS SAT
FROM X
GROUP BY TRUNC(D, 'DAY')
ORDER BY TRUNC(D, 'DAY')

Solution #5: Present each calendar week as a single column value – using LISTAGG function

WITH X AS (
SELECT TRUNC(SYSDATE, 'MON')+level-1 d
FROM DUAL
CONNECT BY MONTHS_BETWEEN(TRUNC(SYSDATE, 'MON')+LEVEL-1, TRUNC(SYSDATE, 'MON'))<1
), y AS (
SELECT LISTAGG(TO_CHAR(d,'DD'), '  ') WITHIN GROUP(ORDER BY d) AS week, TRUNC(D, 'DAY') wday
FROM X
GROUP BY TRUNC(D, 'DAY')
)
SELECT CASE WHEN week LIKE '01%' THEN LPAD(week, 26)
ELSE week
END AS "SUN MON TUE WED THU FRI SAT"
FROM y
ORDER BY wday

Solution #6: Present each calendar week as a single column value – using SYS_CONNECT_BY_PATH function

WITH X AS (
SELECT TRUNC(SYSDATE, 'MON')+level-1 d
FROM DUAL
CONNECT BY MONTHS_BETWEEN(TRUNC(SYSDATE, 'MON')+LEVEL-1, TRUNC(SYSDATE, 'MON'))<1
)
SELECT CASE WHEN MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' ')) LIKE ' 01%' THEN
LPAD(MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' ')), 21)
ELSE MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' '))
END " SU MO TU WE TH FR SA"
FROM x
CONNECT BY d=PRIOR d+1 AND TRUNC(d,'DAY')=TRUNC(PRIOR d, 'DAY')
GROUP BY TRUNC(d, 'DAY')
ORDER BY 1

Solution #7: A variation of Solution #6

SELECT CASE
WHEN MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' ')) LIKE ' 01%' THEN
LPAD(MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' ')), 21)
ELSE MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' '))
END " SU MO TU WE TH FR SA"
FROM (SELECT TRUNC(SYSDATE, 'MON')+level-1 d
FROM DUAL
CONNECT BY MONTHS_BETWEEN(TRUNC(SYSDATE, 'MON')+LEVEL-1, TRUNC(SYSDATE, 'MON'))<1) x
CONNECT BY d=PRIOR d+1 AND TRUNC(d,'DAY')=TRUNC(PRIOR d, 'DAY')