Insert into a Informix table or update if exists - sql

Question

I want to add a row to an Informix database table, but when a row exists with the same unique key I want to update the row.
I have found a solution for MySQL here which is as follows but I need it for Informix:
INSERT INTO table (id, name, age) VALUES(1, "A", 19) ON DUPLICATE KEY UPDATE name="A", age=19

Answer 1

You probably should use the MERGE statement.
Given a suitable table:
create table table (id serial not null primary key, name varchar(20) not null, age integer not null);
this SQL works:
MERGE INTO table AS dst
USING (SELECT 1 AS id, 'A' AS name, 19 AS age
FROM sysmaster:'informix'.sysdual
) AS src
ON dst.id = src.id
WHEN NOT MATCHED THEN INSERT (dst.id, dst.name, dst.age)
VALUES (src.id, src.name, src.age)
WHEN MATCHED THEN UPDATE SET dst.name = src.name, dst.age = src.age
Informix has interesting rules allowing the use of keywords as identifiers without needing double quotes (indeed, unless you have DELIMIDENT set in the environment, double quotes are simply an alternative to single quotes around strings).

Answer 2

You can try the same behavior using the MERGE statement:
Example, creation of the target table:
CREATE TABLE target
(
id SERIAL PRIMARY KEY CONSTRAINT pk_tst,
name CHAR(1),
age SMALLINT
);
Create a temporary source table and insert the record you want:
CREATE TEMP TABLE source
(
id INT,
name CHAR(1),
age SMALLINT
) WITH NO LOG;
INSERT INTO source (id, name, age) VALUES (1, 'A', 19);
The MERGE would be:
MERGE INTO target AS t
USING source AS s ON t.id = s.id
WHEN MATCHED THEN
UPDATE
SET t.name = s.name, t.age = s.age
WHEN NOT MATCHED THEN
INSERT (id, name, age)
VALUES (s.id, s.name, s.age);
You'll see that the record was inserted then you can:
UPDATE source
SET age = 20
WHERE id = 1;
And test the MERGE again.
Another way to do it is create a stored procedure, basically you will do the INSERT statement and check the SQL error code, if it's -100 you go for the UPDATE.
Something like:
CREATE PROCEDURE sp_insrt_target(v_id INT, v_name CHAR(1), v_age SMALLINT)
ON EXCEPTION IN (-100)
UPDATE target
SET name = v_name, age = v_age
WHERE id = v_id;
END EXCEPTION
INSERT INTO target VALUES (v_id, v_name, v_age);
END PROCEDURE;