[size=medium]I didn't care of the foreign key before, today I have find my problem with it.
[color=red]The foreign key must be fllow some constraints.[/color]
For example, I have two tables, one named A and one named B. The B table has a column references of the column of A table, and this column in the A table must be [color=red]a constraint of unique[/color] or [color=red]primary[/color].
Just my note.
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