select column only if it exists

i need to display tablespace attributes SQL> select tablespace_name, status, contents, logging, extent_management, allocation_type, segment_space_management, retention, bigfile from dba_tablespaces; TABLESPACE_NAME STATUS CONTENTS LOGGING EXTENT_MAN ALLOCATIO SEGMEN RETENTION BIG ——————– ——— ——— ——— ———- ——— —— ———– — SYSTEM ONLINE PERMANENT LOGGING LOCAL SYSTEM MANUAL NOT APPLY NO looks fine. but what if I try that […]

dynamic number of columns

probably one of the most frequently asked question, you want to have a table like             ACCOUNTING OPERATIONS RESEARCH SALES ANALYST              0          0        2     0 CLERK                1          0        2     1 MANAGER              0          0        1     1 PRESIDENT            1          0        0     0 SALESMAN             0          0        0     4 but the number and name of columns must be dynamic. typically, I answer : this is not possible in plain sql. you need to use plsql. well. It is not too much beautifoul, but […]

TO_CHAR(…, ‘D’)

How do I get than MONDAY=1, TUESDAY=2, WEDNESDAY=3 … ? With to_char() alter session set nls_territory=germany; select to_char(sysdate,’DAY D’) from dual; TUESDAY 2 With decode() select decode(to_char(sysdate, ‘FMDAY’, ‘NLS_DATE_LANGUAGE=american’),’MONDAY’, ‘1’, ‘TUESDAY’, ‘2’, ‘…’)) from dual; With mod() As a reference, I take monday Jan 1st, 1000. select mod(trunc(sysdate)-date ‘1000-01-01’,7)+1 from dual; 2 How do I […]

sys_connect_by_path

sys_connect_by_path is the only function provided by Oracle to get the the hierarchy path in one field, and it is only concatenating. I just found out a way of doing a sum of the path : let’s imagine I want the sum of the salary of all my hierarchy. select ename, sys_connect_by_path(ename,’/’) hierarchy, length(replace(sys_connect_by_path(lpad(‘ ‘,sal/10),’/’),’/’))*10 […]

Oracle analytics in basic sql queries

When I first saw analytics appearing in Oracle last century, I did not realised they were going to change my way of writting basic SQL queries. Some (Variance, deviance) are truely mathematical and still reserved for statistical analysis. Here I will try to describe ROW_NUMBER : Back in Oracle 7, I remember to have written […]