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
}
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)
}