Notes on left join query (LEFT JOIN)
The left join query condition (ON) should ensure that the condition is unique, otherwise multiple values will be generated
Example:
Select c. Cardholder cc. Cardholder number from `vip_card_ change` as cc left join `vip_ card` as c on cc.card_number=c.card_number and cc.store_key=c.store_key
Instead of:
Select c. Cardholder cc. Cardholder number from `vip_card_ change` as cc left join `vip_ card` as c on cc.card_number=c.card_number
