如果表中不存在列值，则将行插入表中

Question

I have the following query:

INSERT INTO LICENSE_TABLE
(code, license_type, distributor)
values ("uniquecode", "standard", "walmart")

I want to insert the row only if no row exists that already has code="uniquecode"

How can I do this?

I found some solutions involving INSERT IGNORE , something about DUAL , and a few more, but I did not understand which applies to my situation.

If it matters, I am using pymysql .

Answer 1

The best way to do this uses on duplicate key update :

First, you need a unique index, so the database maintains the data integrity.

Second:

INSERT INTO LICENSE_TABLE (code, license_type, distributor)
    VALUES ('uniquecode', 'standard', 'walmart')
    ON DUPLICATE KEY UPDATE code = VALUES(code);

This is better than a WHERE subquery with EXISTS because it is thread-safe . That means that multiple updates in different threads will not ever cause a problem.

This is better than INSERT IGNORE because INSERT IGNORE will ignore other errors. ON DUPLICATE KEY UPDATE does exactly what you want.

Answer 2

You should first create a UNIQUE INDEX on the code column. You can then safely insert the data without warnings using:

INSERT INTO LICENSE_TABLE(code, license_type, distributor)
SELECT 'uniquecode', 'standard', 'walmart'
FROM (SELECT 1) AS x
WHERE NOT EXISTS (
    SELECT 1
    FROM LICENSE_TABLE
    WHERE code = 'uniquecode'
)

Answer 3

Just use INSERT IGNORE like

INSERT IGNORE INTO LICENSE_TABLE
(code, license_type, distributor)
values ("uniquecode", "standard", "walmart")

But you need to have a unique index on the code column. Check if you have one already either with show indexes from LICENSE_TABLE; or show create table LICENSE_TABLE;

If you don't have one, you can create one like this:

create unique index uidx_license_table_code on LICENSE_TABLE(code);