Find if a column in Oracle has a sequence

Question

I am attempting to figure out if a column in Oracle is populated from a sequence. My impression of how Oracle handles sequencing is that the sequence and column are separate entities and one needs to either manually insert the next sequence value like:

insert into tbl1 values(someseq.nextval, 'test')

or put it into a table trigger. Meaning that it is non-trivial to tell if a column is populated from a sequence. Is that correct? Any ideas about how I might go about figuring out if a column is populated from a sequence?

Answer 1

You are correct; the sequence is separate from the table, and a single sequence can be used to populate any table, and the values in a column in some table may mostly come from a sequence (or set of sequences), except for the values manually generated.

In other words, there is no mandatory connection between a column and a sequence - and therefore no way to discover such a relationship from the schema.

Ultimately, the analysis will be of the source code of all applications that insert or update data in the table. Nothing else is guaranteed. You can reduce the scope of the search if there is a stored procedure that is the only way to make modifications to the table, or if there is a trigger that sets the value, or other such things. But the general solution is the 'non-solution' of 'analyze the source'.

Answer 2

If the sequence is used in a trigger, it is possible to find which tables it populates:

SQL> select t.table_name, d.referenced_name as sequence_name
  2  from   user_triggers t
  3         join user_dependencies d
  4         on d.name = t.trigger_name
  5  where  d.referenced_type = 'SEQUENCE'
  6  and    d.type = 'TRIGGER'
  7  /

TABLE_NAME                     SEQUENCE_NAME
------------------------------ ------------------------------
EMP                            EMPNO_SEQ

SQL>

You can vary this query to find stored procedures, etc that make use of the sequence.

Answer 3

There are no direct metadata links between Oracle sequences and any use in the database. You could make an intelligent guess if a column's values are related to a sequence by querying the USER_SEQUENCES metadata and comparing the LAST_NUMBER column to the data for the column.

Answer 4

select t.table_name,
   d.referenced_name  as sequence_name,
   d.REFERENCED_OWNER as "OWNER",
   c.COLUMN_NAME
  from user_trigger_cols t, user_dependencies d, user_tab_cols c
 where d.name = t.trigger_name
   and t.TABLE_NAME = c.TABLE_NAME
   and t.COLUMN_NAME = c.COLUMN_NAME
   and d.referenced_type = 'SEQUENCE'
   and d.type = 'TRIGGER'

Answer 5

As Jonathan pointed out: there is no direct way to relate both objects. However, if you "keep a standard" for primary keys and sequences/triggers you could find out by finding the primary key and then associate the constraint to the table sequence.

I was in need of something similar since we are building a multi-db product and I tried to replicate some classes with properties found in a DataTable object from .Net which has AutoIncrement, IncrementSeed and IncrementStep which can only be found in the sequences.

So, as I said, if you, for your tables, use a PK and always have a sequence associated with a trigger for inserts on a table then this may come handy:

select tc.table_name,
  case tc.nullable 
    when 'Y' then 1
    else 0
  end as is_nullable,
  case ac.constraint_type 
    when 'P' then 1
    else 0
  end as is_identity,
  ac.constraint_type,
  seq.increment_by as auto_increment_seed,
  seq.min_value as auto_increment_step,
  com.comments as caption,
  tc.column_name,
  tc.data_type,
  tc.data_default as default_value,
  tc.data_length as max_length,
  tc.column_id,
  tc.data_precision as precision,
  tc.data_scale as scale
from SYS.all_tab_columns tc
left outer join SYS.all_col_comments com
  on (tc.column_name = com.column_name and tc.table_name = com.table_name)
LEFT OUTER JOIN  SYS.ALL_CONS_COLUMNS CC 
  on (tc.table_name = cc.table_name and tc.column_name = cc.column_name and tc.owner = cc.owner)
LEFT OUTER JOIN SYS.ALL_CONSTRAINTS AC
  ON (ac.constraint_name = cc.constraint_name and ac.owner = cc.owner)
LEFT outer join user_triggers trg
  on (ac.table_name = trg.table_name and ac.owner = trg.table_owner)
LEFT outer join user_dependencies dep
  on (trg.trigger_name = dep.name and dep.referenced_type='SEQUENCE' and dep.type='TRIGGER')
LEFT outer join user_sequences seq
  on (seq.sequence_name = dep.referenced_name)  
where tc.table_name = 'TABLE_NAME'
and tc.owner = 'SCHEMA_NAME'
AND AC.CONSTRAINT_TYPE = 'P'
union all
select tc.table_name,
  case tc.nullable 
    when 'Y' then 1
    else 0
  end as is_nullable,
  case ac.constraint_type 
    when 'P' then 1
    else 0
  end as is_identity,
  ac.constraint_type,
  seq.increment_by as auto_increment_seed,
  seq.min_value as auto_increment_step,
  com.comments as caption,
  tc.column_name,
  tc.data_type,
  tc.data_default as default_value,
  tc.data_length as max_length,
  tc.column_id,
  tc.data_precision as precision,
  tc.data_scale as scale
from SYS.all_tab_columns tc
left outer join SYS.all_col_comments com
  on (tc.column_name = com.column_name and tc.table_name = com.table_name)
LEFT OUTER JOIN  SYS.ALL_CONS_COLUMNS CC 
  on (tc.table_name = cc.table_name and tc.column_name = cc.column_name and tc.owner = cc.owner)
LEFT OUTER JOIN SYS.ALL_CONSTRAINTS AC
  ON (ac.constraint_name = cc.constraint_name and ac.owner = cc.owner)
LEFT outer join user_triggers trg
  on (ac.table_name = trg.table_name and ac.owner = trg.table_owner)
LEFT outer join user_dependencies dep
  on (trg.trigger_name = dep.name and dep.referenced_type='SEQUENCE' and dep.type='TRIGGER')
LEFT outer join user_sequences seq
  on (seq.sequence_name = dep.referenced_name)  
where tc.table_name = 'TABLE_NAME'
and tc.owner = 'SCHEMA_NAME'
AND AC.CONSTRAINT_TYPE is null;

That would give you the list of columns for a schema/table with:

• Table name
• If column is nullable
• Constraint type (only for PK's)
• Increment seed (from the sequence)
• Increment step (from the sequence)
• Column comments
• Column name, of course :)
• Data type
• Default value, if any
• Length of column
• Index (column id)
• Precision (for numbers)
• Scale (for numbers)

I'm pretty sure that code can be optimized but it works for me, I use it to "load metadata" for tables and then represent that metadata as entities on my frontend.

Note that I'm filtering only primary keys and not retrieving compound key constraints since I don't care about those. If you do you'll have to modify the code to do so and make sure that you filter duplicates since you could get one column twice (one for the PK constraint, another for the compound key).