PostgreSQL Insert with failed unique constraint - postgresql

Question

CREATE TABLE s_etpta.sfphierg (
hierar VARCHAR(10) NOT NULL,
libelle VARCHAR(40),
typfct VARCHAR(1),
utilcre VARCHAR(10),
datcre DATE,
utilmod VARCHAR(10),
datmod DATE,
CONSTRAINT i_sfphierg PRIMARY KEY(hierar)
)
CREATE TABLE s_etpta.hopsech (
horsect VARCHAR(40) NOT NULL,
libelle VARCHAR(40),
libcourt VARCHAR(20),
horcode VARCHAR(10),
CONSTRAINT i_hopsech PRIMARY KEY(horsect)
)
BEGIN
delete from SFPHIERG;
INSERT INTO SFPHIERG ("hierar", "libelle", "typfct", "utilcre", "datcre",
"utilmod", "datmod")
select '01'||horcode, E'Hircuit standard'||horcode, E'1', E'HQS', E'2007-01-
29', E' ', E'1900-01-01'
FROM HOPSECH where HOPSECH.IJIGHSUPPM like '1'
and not exists (select hierar from SFPHIERG where hierar like '01'||horcode);
INSERT INTO SFPHIERG ("hierar", "libelle", "typfct", "utilcre", "datcre",
"utilmod", "datmod")
select '00'||horcode, E'Circuit cascade'||horcode, E'1', E'HQS', E'2007-01-
29', E' ', E'1900-01-01'
FROM HOPSECH where HOPSECH.IJIGHSUPPR like '1'
and not exists (select hierar from SFPHIERG where hierar like '00'||horcode);
END;
In my functions's body I have two insert queries executed after a delete query.
The rows are correctly inserted when my first column doesn't exist, when it does I have the failed unique constraint error, when this error occur nothing is added into my table.
Is there a way I can stop this error from blocking all the inserts and only the inserts where my first column exists?