Пример #1
0
func simplifyComparisonExpr(n *parser.ComparisonExpr) (parser.TypedExpr, bool) {
	// NormalizeExpr will have left comparisons in the form "<var> <op>
	// <datum>" unless they could not be simplified further in which case
	// simplifyExpr cannot handle them. For example, "lower(a) = 'foo'"
	left, right := n.TypedLeft(), n.TypedRight()
	if isVar(left) && isDatum(right) {
		if right == parser.DNull {
			switch n.Operator {
			case parser.IsNotDistinctFrom:
				switch left.(type) {
				case *qvalue, *parser.IndexedVar:
					// Transform "a IS NOT DISTINCT FROM NULL" into "a IS NULL".
					return parser.NewTypedComparisonExpr(
						parser.Is,
						left,
						right,
					), true
				}
			case parser.IsDistinctFrom:
				switch left.(type) {
				case *qvalue, *parser.IndexedVar:
					// Transform "a IS DISTINCT FROM NULL" into "a IS NOT NULL".
					return parser.NewTypedComparisonExpr(
						parser.IsNot,
						left,
						right,
					), true
				}
			case parser.Is, parser.IsNot:
				switch left.(type) {
				case *qvalue, *parser.IndexedVar:
					// "a IS {,NOT} NULL" can be used during index selection to restrict
					// the range of scanned keys.
					return n, true
				}
			default:
				// All of the remaining comparison operators have the property that when
				// comparing to NULL they evaluate to NULL (see evalComparisonOp). NULL is
				// not the same as false, but in the context of a WHERE clause, NULL is
				// considered not-true which is the same as false.
				return parser.MakeDBool(false), true
			}
		}

		switch n.Operator {
		case parser.EQ:
			// Translate "(a, b) = (1, 2)" to "(a, b) IN ((1, 2))".
			switch left.(type) {
			case *parser.Tuple:
				return parser.NewTypedComparisonExpr(
					parser.In,
					left,
					&parser.DTuple{right.(parser.Datum)},
				), true
			}
			return n, true
		case parser.NE, parser.GE, parser.LE:
			return n, true
		case parser.GT:
			// This simplification is necessary so that subsequent transformation of
			// > constraint to >= can use Datum.Next without concern about whether a
			// next value exists. Note that if the variable (n.Left) is NULL, this
			// comparison would evaluate to NULL which is equivalent to false for a
			// boolean expression.
			if right.(parser.Datum).IsMax() {
				return parser.MakeDBool(false), true
			}
			return n, true
		case parser.LT:
			// Note that if the variable is NULL, this would evaluate to NULL which
			// would equivalent to false for a boolean expression.
			if right.(parser.Datum).IsMin() {
				return parser.MakeDBool(false), true
			}
			return n, true
		case parser.In, parser.NotIn:
			tuple := *right.(*parser.DTuple)
			if len(tuple) == 0 {
				return parser.MakeDBool(false), true
			}
			return n, true
		case parser.Like:
			// a LIKE 'foo%' -> a >= "foo" AND a < "fop"
			if d, ok := right.(*parser.DString); ok {
				if i := strings.IndexAny(string(*d), "_%"); i >= 0 {
					return makePrefixRange((*d)[:i], left, false), false
				}
				return makePrefixRange(*d, left, true), false
			}
			// TODO(pmattis): Support parser.DBytes?
		case parser.SimilarTo:
			// a SIMILAR TO "foo.*" -> a >= "foo" AND a < "fop"
			if d, ok := right.(*parser.DString); ok {
				pattern := parser.SimilarEscape(string(*d))
				if re, err := regexp.Compile(pattern); err == nil {
					prefix, complete := re.LiteralPrefix()
					return makePrefixRange(parser.DString(prefix), left, complete), false
				}
			}
			// TODO(pmattis): Support parser.DBytes?
		}
	}
	return parser.MakeDBool(true), false
}
Пример #2
0
func simplifyComparisonExpr(n *parser.ComparisonExpr) parser.Expr {
	// NormalizeExpr will have left comparisons in the form "<var> <op>
	// <datum>" unless they could not be simplified further in which case
	// simplifyExpr cannot handle them. For example, "lower(a) = 'foo'"
	if isVar(n.Left) && isDatum(n.Right) {
		// All of the comparison operators have the property that when comparing to
		// NULL they evaluate to NULL (see evalComparisonOp). NULL is not the same
		// as false, but in the context of a WHERE clause, NULL is considered
		// not-true which is the same as false.
		if n.Right == parser.DNull {
			return parser.DBool(false)
		}

		switch n.Operator {
		case parser.EQ, parser.NE, parser.GE, parser.LE:
			return n
		case parser.GT:
			// This simplification is necessary so that subsequent transformation of
			// > constraint to >= can use Datum.Next without concern about whether a
			// next value exists. Note that if the variable (n.Left) is NULL, this
			// comparison would evaluate to NULL which is equivalent to false for a
			// boolean expression.
			if n.Right.(parser.Datum).IsMax() {
				return parser.DBool(false)
			}
			return n
		case parser.LT:
			// Note that if the variable is NULL, this would evaluate to NULL which
			// would equivalent to false for a boolean expression.
			if n.Right.(parser.Datum).IsMin() {
				return parser.DBool(false)
			}
			return n
		case parser.In, parser.NotIn:
			tuple := n.Right.(parser.DTuple)
			sort.Sort(tuple)
			tuple = uniqTuple(tuple)
			if len(tuple) == 0 {
				return parser.DBool(false)
			}
			n.Right = tuple
			return n
		case parser.Like:
			// a LIKE 'foo%' -> a >= "foo" AND a < "fop"
			if d, ok := n.Right.(parser.DString); ok {
				if i := strings.IndexAny(string(d), "_%"); i >= 0 {
					return makePrefixRange(d[:i], n.Left, false)
				}
				return makePrefixRange(d, n.Left, true)
			}
			// TODO(pmattis): Support parser.DBytes?
		case parser.SimilarTo:
			// a SIMILAR TO "foo.*" -> a >= "foo" AND a < "fop"
			if d, ok := n.Right.(parser.DString); ok {
				pattern := parser.SimilarEscape(string(d))
				if re, err := regexp.Compile(pattern); err == nil {
					prefix, complete := re.LiteralPrefix()
					return makePrefixRange(parser.DString(prefix), n.Left, complete)
				}
			}
			// TODO(pmattis): Support parser.DBytes?
		}
	}
	return parser.DBool(true)
}