Depending on what PHP functions you are using, the problem could have resulted there.
There was really no need to convert the column to type char, but, rather, use a different function.
For example, the function mktime(), I believe, only works with dates after 1/1/1970. There are definitely ways around this.
*cLFlaVA
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Ham and Eggs walks into a bar and asks, "Can I have a beer please?"
The bartender replies, "I'm sorry, we don't serve breakfast.