The SQL standard states
An implementation-defined completion condition shall be indicated by
returning an implementation-defined subclass in conjunction with one of
the classes successful completion, warning, or no data.
In other words, an info, notice, or warning must have a class 00, 01, 02.
However, I noticed several warnings that use codes that are intended for
errors, for example in portalcmds.c and xact.c.
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Peter Eisentraut peter_e(at)gmx(dot)net