Help with LEFT JOIN

[Anon]

tbl1

C1 | C2 |

6 | 3 |

2 | 9 |

tbl2

C1 | C2 | C3 |

6 | 3 | 21 |

2 | 9 | 21 |

I want to dynamically derive table 2 from table 1.

tbl2.C3 contains values calculated from tbl1.c1 and tbl1.c2.

I cannot hard code c3, because the calculation used to get C3 is based on a user's choice.

What I need help with is a way to do a LEFT JOIN to tbl1 to get tbl2, and finally be able to issue a mysql query on tbl2 similar to this:

select * from tbl2 where c3 <= 'someval'

Thanks for the help.

Richard.

[[deleted]]

a LEFT JOIN is usually not what you want.

What exactly do you have in your tbl1 and tbl2, and what do you want to calculate?