PL/SQL - Operator Precedence

Hi all, It has been almost an year since I posted a topic in this blog. After a 1 year study break, I back to my usual job and hopfully I am become regular in this blog again.


In SQL or PL/SQL we use several operators. Some are mathematical, logical and comparison operatiors. Oracle follow a order of precedence when execute an expression that contains more than one operators. If operatiors with same precidence are occured then it does not follow any order. Otherwise Oracle maintain the following order of precedence of operators.


Order |------------| Operator |------------| Operation
1 |------------| ** |------------| exponentiation
2 |------------| +, |------------| identity, negation
3 |------------| *, / |------------| multiplication, division
4 |------------| +, -, || |------------| addition, subtraction, concatenation
5 |------------| =, <, >, <=, >=, |------------| comparison
<>, !=, ~=, ^=, IS NULL, LIKE,
BETWEEN, IN
6 |------------| NOT |------------| logical negation
7 |------------| AND |------------| conjunction
8 |------------| OR |------------| inclusion


For example, when NOT, AND and OR operators are used in the same statement NOT is evaluated first, then AND and finally OR.

Estimate Tablespace growth

Some time it is very helpful to plan disk space/ tablespace management if you estimate the growth of your tablespace. Here is a select query which can be helpful :

SELECT TO_CHAR (sp.begin_interval_time,'DD-MM-YYYY') days
, ts.tsname
, max(round((tsu.tablespace_size* dt.block_size )/(1024*1024),2) ) cur_size_MB
, max(round((tsu.tablespace_usedsize* dt.block_size )/(1024*1024),2)) usedsize_MB
FROM DBA_HIST_TBSPC_SPACE_USAGE tsu
, DBA_HIST_TABLESPACE_STAT ts
, DBA_HIST_SNAPSHOT sp
, DBA_TABLESPACES dt
WHERE tsu.tablespace_id= ts.ts#
AND tsu.snap_id = sp.snap_id
AND ts.tsname = dt.tablespace_name
AND ts.tsname NOT IN ('SYSAUX','SYSTEM')
GROUP BY TO_CHAR (sp.begin_interval_time,'DD-MM-YYYY'), ts.tsname
ORDER BY ts.tsname, days;


Another One: This query gives average increase per day 

SELECT b.tsname tablespace_name
, MAX(b.used_size_mb) cur_used_size_mb
, round(AVG(inc_used_size_mb),2)avg_increas_mb
FROM (
  SELECT a.days, a.tsname, used_size_mb
  , used_size_mb - LAG (used_size_mb,1)  OVER ( PARTITION BY a.tsname ORDER BY a.tsname,a.days) inc_used_size_mb
  FROM (
      SELECT TO_CHAR(sp.begin_interval_time,'MM-DD-YYYY') days
       ,ts.tsname
       ,MAX(round((tsu.tablespace_usedsize* dt.block_size )/(1024*1024),2)) used_size_mb
      FROM DBA_HIST_TBSPC_SPACE_USAGE tsu, DBA_HIST_TABLESPACE_STAT ts
       ,DBA_HIST_SNAPSHOT sp, DBA_TABLESPACES dt
      WHERE tsu.tablespace_id= ts.ts# AND tsu.snap_id = sp.snap_id
       AND ts.tsname = dt.tablespace_name  AND sp.begin_interval_time > sysdate-7
      GROUP BY TO_CHAR(sp.begin_interval_time,'MM-DD-YYYY'), ts.tsname
      ORDER BY ts.tsname, days
  ) A
) b GROUP BY b.tsname ORDER BY b.tsname;