SQlite: select with insert if not exist - sql

Question

Let's suppose we have a table defined with:
CREATE TABLE IF NOT EXISTS signals(sigid INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT)
This table initially is empty.
I would like to get the sigid for a given name with a select and in case name does not exist, add it and get the new autoincremented id.
I would like to use this query in order to autogenerate ,when needed, a new id that is used as foreign key in another table. I must put attention to the performances so I cannot proceed as :
check if name is present and return id witha a SELECT
if returned id is null create a new entry with an INSERT
get the new id again with a new SELECT
Is it possible do it with a single SELECT-like query ?
Thanks!

Answer 1

i think with an single select no.
Let's say i want to insert id_build = 3, hashed_value = 1 into the big table 'crash'.
The code in example makes first select to check if the value was already in the table, if yes skips the insert with where .. is null then retrive the id from already saved into temporary table.
example :
create temporary table if not exists Variablez(Name TEXT primary key on conflict replace, Value TEXT); --storing vars
insert into Variablez(Name, Value) values ('tmp_id', (select id_crash from crash where hashed_value = "1" )); --put id if was existing
insert into crash(id_build, hashed_value) select 3, 1 where (select Value from Variablez where Name = 'tmp_id' ) is null; -- insert if not exists
select
case
when (select Value from Variablez where name = 'tmp_id' ) is null then
'0'
else
'1'
end
as existing,
case
when (select Value from Variablez where name = 'tmp_id' ) is null then
(select id_crash from crash where hashed_value = "1")
else
(select Value from Variablez where name = 'tmp_id')
end
as id_returned;

Answer 2

if the table is empty and you are the one filling it in just one shot (and you don't need to do it again later on when there is data in the table), AND you don't have too many rows, then you could just cache the names you have already inserted and look them up in memory.
It's more of a comment, I guess.
there is also this for getting the last inserted id:
SELECT last_insert_rowid();
But if the above applies, you are even faster by assigning the ids yourself, and not define it as AUTOINCREMENT. Then you don't need to get the last inserted id, you just keep a counter and all the names inserted and increment for each new name you find.
CREATE TABLE IF NOT EXISTS signals(sigid INTEGER PRIMARY KEY NOT NULL, name TEXT)
List<String> insertedNames = new List<String>();
int count = 0;
while(input.hasNext())
{
String name = input.next();
if( !insertedNames.contains(name) )
{
var sql = "insert into table (sigid,name) VALUES (" + count + ", " + name + ")";
executeSql(sql);
insertedNames.add(name);
count++;
}
}
answering your comment
public int getId( string name )
{
String sql = "select id from table where name='" + name + "'";
int theIdForTheName = executeAndGetFirstColumnAsInt(sql);
return theIdForTheName;
}
i don't know what else to tell you...