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expression: support ConstItem() for expression (#10004) #10167

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expression: support ConstItem() for expression (#10004) #10167

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10 changes: 10 additions & 0 deletions expression/column.go
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Original file line number Diff line number Diff line change
Expand Up @@ -124,6 +124,11 @@ func (col *CorrelatedColumn) IsCorrelated() bool {
return true
}

// ConstItem implements Expression interface.
func (col *CorrelatedColumn) ConstItem() bool {
return false
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We just set it to true?

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I'm afraid it would cause some other problems.
For example, when building some scalar function like from_unixtime(CorCol), we may use it to decide if we can evaluate the argument at that time.
If it is true, we may call CorCol.Eval(NullRow) and this function call is invalid.

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@qw4990 qw4990 Apr 17, 2019 •
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In my opinion, ConstItem means 1) this expression has no column reference, 2) this expression doesn't include some special scalar functions which behave differently according to time like Rand and SysDate.
CorrelatedColumn breaks the rule 1).
Maybe name ConsistentItem is more closer to its meaning.

}

// Decorrelate implements Expression interface.
func (col *CorrelatedColumn) Decorrelate(schema *Schema) Expression {
if !schema.Contains(&col.Column) {
Expand Down Expand Up @@ -296,6 +301,11 @@ func (col *Column) IsCorrelated() bool {
return false
}

// ConstItem implements Expression interface.
func (col *Column) ConstItem() bool {
return false
}

// Decorrelate implements Expression interface.
func (col *Column) Decorrelate(_ *Schema) Expression {
return col
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1 change: 1 addition & 0 deletions expression/column_test.go
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Expand Up @@ -43,6 +43,7 @@ func (s *testEvaluatorSuite) TestColumn(c *C) {
c.Assert(corCol.Equal(nil, corCol), IsTrue)
c.Assert(corCol.Equal(nil, invalidCorCol), IsFalse)
c.Assert(corCol.IsCorrelated(), IsTrue)
c.Assert(corCol.ConstItem(), IsFalse)
c.Assert(corCol.Decorrelate(schema).Equal(nil, col), IsTrue)
c.Assert(invalidCorCol.Decorrelate(schema).Equal(nil, invalidCorCol), IsTrue)

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5 changes: 5 additions & 0 deletions expression/constant.go
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Expand Up @@ -316,6 +316,11 @@ func (c *Constant) IsCorrelated() bool {
return false
}

// ConstItem implements Expression interface.
func (c *Constant) ConstItem() bool {
return true
}

// Decorrelate implements Expression interface.
func (c *Constant) Decorrelate(_ *Schema) Expression {
return c
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8 changes: 8 additions & 0 deletions expression/expression.go
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Expand Up @@ -80,6 +80,14 @@ type Expression interface {
// IsCorrelated checks if this expression has correlated key.
IsCorrelated() bool

// ConstItem checks if this expression is constant item, regardless of query evaluation state.
// An expression is constant item if it:
// refers no tables.
// refers no subqueries that refers any tables.
// refers no non-deterministic functions.
// refers no statement parameters.
ConstItem() bool

// Decorrelate try to decorrelate the expression by schema.
Decorrelate(schema *Schema) Expression

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14 changes: 14 additions & 0 deletions expression/expression_test.go
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Expand Up @@ -61,6 +61,7 @@ func (s *testEvaluatorSuite) TestConstant(c *C) {

sc := &stmtctx.StatementContext{TimeZone: time.Local}
c.Assert(Zero.IsCorrelated(), IsFalse)
c.Assert(Zero.ConstItem(), IsTrue)
c.Assert(Zero.Decorrelate(nil).Equal(s.ctx, Zero), IsTrue)
c.Assert(Zero.HashCode(sc), DeepEquals, []byte{0x0, 0x8, 0x0})
c.Assert(Zero.Equal(s.ctx, One), IsFalse)
Expand All @@ -85,6 +86,19 @@ func (s *testEvaluatorSuite) TestIsBinaryLiteral(c *C) {
c.Assert(IsBinaryLiteral(con), IsFalse)
}

func (s *testEvaluatorSuite) TestConstItem(c *C) {
defer testleak.AfterTest(c)()

sf := newFunction(ast.Rand)
c.Assert(sf.ConstItem(), Equals, false)
sf = newFunction(ast.UUID)
c.Assert(sf.ConstItem(), Equals, false)
sf = newFunction(ast.GetParam, One)
c.Assert(sf.ConstItem(), Equals, false)
sf = newFunction(ast.Abs, One)
c.Assert(sf.ConstItem(), Equals, true)
}

type testTableBuilder struct {
tableName string
columnNames []string
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14 changes: 14 additions & 0 deletions expression/scalar_function.go
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Expand Up @@ -152,6 +152,20 @@ func (sf *ScalarFunction) IsCorrelated() bool {
return false
}

// ConstItem implements Expression interface.
func (sf *ScalarFunction) ConstItem() bool {
// Note: some unfoldable functions are deterministic, we use unFoldableFunctions here for simplification.
if _, ok := unFoldableFunctions[sf.FuncName.L]; ok {
return false
}
for _, arg := range sf.GetArgs() {
if !arg.ConstItem() {
return false
}
}
return true
}

// Decorrelate implements Expression interface.
func (sf *ScalarFunction) Decorrelate(schema *Schema) Expression {
for i, arg := range sf.GetArgs() {
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1 change: 1 addition & 0 deletions expression/scalar_function_test.go
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Expand Up @@ -40,6 +40,7 @@ func (s *testEvaluatorSuite) TestScalarFunction(c *C) {
c.Assert(err, IsNil)
c.Assert(res, DeepEquals, []byte{0x22, 0x6c, 0x74, 0x28, 0x66, 0x65, 0x69, 0x2e, 0x68, 0x61, 0x6e, 0x2c, 0x20, 0x31, 0x29, 0x22})
c.Assert(sf.IsCorrelated(), IsFalse)
c.Assert(sf.ConstItem(), IsFalse)
c.Assert(sf.Decorrelate(nil).Equal(s.ctx, sf), IsTrue)
c.Assert(sf.HashCode(sc), DeepEquals, []byte{0x3, 0x4, 0x6c, 0x74, 0x1, 0x80, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x1, 0x0, 0x5, 0xbf, 0xf0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0})

Expand Down