MySQL 8.0

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create table table1 (column1 varchar(20), column2 varchar(20), column3 varchar(20))
create table table2 (column1 varchar(20), column2 varchar(20), column3 varchar(20))
insert into table2 values
('val11', 'val12', 'val13')
select * from table2


column1
column2
column3


val11
val12
val13


INSERT INTO table1 (column1, column2, column3)
SELECT *
FROM (SELECT 'val11' AS column1, 'val12' AS column2, 'val13' AS column3
      UNION
      SELECT 'val21', 'val22', 'val23') v
WHERE NOT EXISTS (SELECT * 
                  FROM table2 t2
                  WHERE t2.column1 = v.column1
                    AND t2.column2 = v.column2
                    AND t2.column3 = v.column3)

Records: 1  Duplicates: 0  Warnings: 0


select * from table1


column1
column2
column3


val21
val22
val23