MySQL Conditional Insert

Question

I am having a difficult time forming a conditional INSERT

I have x_table with columns (instance, user, item) where instance ID is unique. I want to insert a new row

Answer 1

I have found out today that a SELECT statement can have a WHERE condition even if it has no FROM clause and does not read any tables at all.

This makes it very easy to conditionally insert something using this construct:

SELECT ... INTO @condition;
-- or if you prefer: SET @condition = ...

INSERT INTO myTable (col1, col2) SELECT 'Value 1', 'Value 2' WHERE @condition;

Tested this on MySQL 5.7 and MariaDB 10.3.