oracle - What if the value of order field is the same for all the records -

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• why oracle return specific sequence if 'orderby' values identical? 4 answers

all, let's sql looks below.

select a, b ,c table1 order c 

if rows in table1 have same field value in field c. want know if result has same order each time executed sql.

let's data in table1 looks below.

a              b                 c  ------------------------------------------- 1              x1                 2014-4-1 .... 100            x100               2014-4-1  .... 1000           x1000              2014-4-1 .... 

how oracle determine rows sequence same order value?

added

will random sequence each time?

one simple answer no. there no guarantee order by on equal values return same sorted result every time. might seem stable, however, there many reasons when change.

for example, sorting on equal values might defer after:

1. gathering statistics
2. adding index on column

for example,

let's have table t:

sql> select * t order b;                    b ---------- ----------          1          1          2          1          3          2          4          2          5          3          6          3  6 rows selected. 

the sorting on column having similar values like:

sql> create table t1 select * t order b, dbms_random.value;  table created.  sql> select * t1 order b;                    b ---------- ----------          1          1          2          1          4          2          3          2          5          3          6          3  6 rows selected. 

so, similar data in bot tables, however, order by on column having equal values, dos not guarantee same sorting.