	if (vardata->isunique && vardata->rel && vardata->rel->tuples >= 1.0)
	{
		selec = 1.0 / vardata->rel->tuples;
	}
	else if (HeapTupleIsValid(vardata->statsTuple) &&
			 statistic_proc_security_check(vardata,
										   (opfuncoid = get_opcode(oproid))))
…
		if (match)
		{
			/*
			 * Constant is "=" to this common value.  We know selectivity
			 * exactly (or as exactly as ANALYZE could calculate it, anyway).
			 */
			selec = sslot.numbers[i];
		}
		else
		{
			/*
			 * Comparison is against a constant that is neither NULL nor any
			 * of the common values.  Its selectivity cannot be more than
			 * this:
			 */
			double		sumcommon = 0.0;
			double		otherdistinct;

			for (i = 0; i < sslot.nnumbers; i++)
				sumcommon += sslot.numbers[i];
			selec = 1.0 - sumcommon - nullfrac;
			CLAMP_PROBABILITY(selec);

			/*
			 * and in fact it's probably a good deal less. We approximate that
			 * all the not-common values share this remaining fraction
			 * equally, so we divide by the number of other distinct values.
			 */
			otherdistinct = get_variable_numdistinct(vardata, &isdefault) -
				sslot.nnumbers;
			if (otherdistinct > 1)
				selec /= otherdistinct;

…
	else
	{
		/*
		 * No ANALYZE stats available, so make a guess using estimated number
		 * of distinct values and assuming they are equally common. (The guess
		 * is unlikely to be very good, but we do know a few special cases.)
		 */
		selec = 1.0 / get_variable_numdistinct(vardata, &isdefault);
	}

Échauffement