With the select max(id) + 1 approach, two sessions inserting simultaneously will see the same current max ID from the table, and both insert the same new ID value. The only way to use this safely is to lock the table before starting the transaction, which is painful and serialises the transactions. (And as Stijn … Read more
RETURNING That’s possible with a single round-trip to the database: INSERT INTO tbl(filename) VALUES (‘my_filename’) RETURNING tbl_id; tbl_id would typically be a serial or IDENTITY (Postgres 10 or later) column. More in the manual. Explicitly fetch value If filename needs to include tbl_id (redundantly), you can still use a single query. Use lastval() or the … Read more
On 11g and prior, create a sequence to increment the column via trigger. See Auto-increment primary key in Pre 12c releases (Identity functionality) For example, TABLE SQL> CREATE TABLE t ( 2 ID NUMBER(10) NOT NULL, 3 text VARCHAR2(50) NOT NULL); Table created. PRIMARY KEY to be populated by the sequence SQL> ALTER TABLE t … Read more
As I noted in my comment, seq has method for dates, seq.Date: seq(as.Date(‘2011-01-01’),as.Date(‘2011-01-31’),by = 1) [1] “2011-01-01” “2011-01-02” “2011-01-03” “2011-01-04” “2011-01-05” “2011-01-06” “2011-01-07” “2011-01-08” [9] “2011-01-09” “2011-01-10” “2011-01-11” “2011-01-12” “2011-01-13” “2011-01-14” “2011-01-15” “2011-01-16” [17] “2011-01-17” “2011-01-18” “2011-01-19” “2011-01-20” “2011-01-21” “2011-01-22” “2011-01-23” “2011-01-24” [25] “2011-01-25” “2011-01-26” “2011-01-27” “2011-01-28” “2011-01-29” “2011-01-30” “2011-01-31”
If you don’t want to retain the ordering of ids, then you can ALTER SEQUENCE seq RESTART WITH 1; UPDATE t SET idcolumn=nextval(‘seq’); I doubt there’s an easy way to do that in the order of your choice without recreating the whole table.
You should use the fact that when you want all permutations of N numbers there are N! possibilities. Therefore each number x from 1..N! encodes such a permutation. Here is a sample that iteratively prints out all permutations of a sting. private static void printPermutationsIterative(String string){ int [] factorials = new int[string.length()+1]; factorials[0] = 1; … Read more
SOG <- c(4,4,0,0,0,3,4,5,0,0,1,2,0,0,0) #run length encoding: tmp <- rle(SOG) #turn values into logicals tmp$values <- tmp$values == 0 #cumulative sum of TRUE values tmp$values[tmp$values] <- cumsum(tmp$values[tmp$values]) #inverse the run length encoding inverse.rle(tmp) #[1] 0 0 1 1 1 0 0 0 2 2 0 0 3 3 3
Yes, SQL 11 has SEQUENCE objects, see SQL Server v.Next (Denali) : Using SEQUENCE. Creating manual sequences is possible, but not recommended. The trick to do a sequence generator is to use UPDATE WITH OUTPUT on a sequences table. Here is pseudo-code: CREATE TABLE Sequences ( Name sysname not null primary key, Sequence bigint not … Read more
You can do this in one line using itertools.groupby: import itertools max(sum(1 for _ in l) for n, l in itertools.groupby(lst))
Just update your trigger to only fire when not given an id. create or replace trigger sa.my_trigger before insert on sa.my_table for each row when (new.id is null) begin select sa.my_sequence.nextval into :new.id from dual; end;