H2 SQL database - INSERT if the record does not exist

问题

I would like initialize a H2 database, but I am not sure if the records exist. If they exist I don't want to do anything, but if they don't exist I would like to write the default values.

Something like this:

IF 'number of rows in ACCESSLEVELS' = 0
INSERT INTO ACCESSLEVELS VALUES
    (0, 'admin'),
    (1, 'SEO'),
    (2, 'sales director'),
    (3, 'manager'),
    (4, 'REP')
    ;

回答1:

The following works for MySQL, PostgreSQL, and the H2 database:

drop table ACCESSLEVELS;

create table ACCESSLEVELS(id int, name varchar(255));

insert into ACCESSLEVELS select * from (
select 0, 'admin' union
select 1, 'SEO' union
select 2, 'sales director' union
select 3, 'manager' union
select 4, 'REP'
) x where not exists(select * from ACCESSLEVELS);

回答2:

MERGE INTO ACCESSLEVELS 
  KEY(ID) 
VALUES (0, 'admin'),
  (1, 'SEO'),
  (2, 'sales director'),
  (3, 'manager'),
  (4, 'REP');

Updates existing rows, and insert rows that don't exist. If no key column is specified, the primary key columns are used to find the row.

回答3:

To do this you can use MySQL Compatibility Mode in H2 database. Starting from 1.4.197 version it supports the following syntax: INSERT IGNORE INTO table_name VALUES ...

From this pull request:

INSERT IGNORE is not supported in Regular mode, you have to enable MySQL compatibility mode explicitly by appending ;MODE=MySQL to your database URL or by executing SET MODE MySQL statement.

From official site:

INSERT IGNORE is partially supported and may be used to skip rows with duplicate keys if ON DUPLICATE KEY UPDATE is not specified.

来源：https://stackoverflow.com/questions/19768051/h2-sql-database-insert-if-the-record-does-not-exist

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sql