forked from dolthub/go-mysql-server
/
columndefault.go
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/
columndefault.go
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// Copyright 2020-2021 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package sql
import (
"fmt"
)
// ColumnDefaultValue is an expression representing the default value of a column. May represent both a default literal
// and a default expression. A nil pointer of this type represents an implicit default value and is thus valid, so all
// method calls will return without error.
type ColumnDefaultValue struct {
// Expression is the expression representing this default value
Expression
// outType converts the output of the expression into this type, when not nil
outType Type
// literal indicates whether the default value is a literal value or expression
literal bool
// returnNil indicates whether a nil value from the default value expression is returned as null or an error
returnNil bool
// parenthesized indicates whether the value was specified in parens or not; this is typically the opposite of the literal field,
// but they can both be false in the case of now/current_timestamp for datetimes and timestamps.
parenthesized bool
}
var _ Expression = (*ColumnDefaultValue)(nil)
// NewColumnDefaultValue returns a new ColumnDefaultValue expression.
func NewColumnDefaultValue(expr Expression, outType Type, representsLiteral bool, parenthesized bool, mayReturnNil bool) (*ColumnDefaultValue, error) {
return &ColumnDefaultValue{
Expression: expr,
outType: outType,
literal: representsLiteral,
returnNil: mayReturnNil,
parenthesized: parenthesized,
}, nil
}
// NewUnresolvedColumnDefaultValue returns a column default
func NewUnresolvedColumnDefaultValue(expr string) *ColumnDefaultValue {
return &ColumnDefaultValue{
Expression: UnresolvedColumnDefault{exprString: expr},
}
}
// Children implements sql.Expression
func (e *ColumnDefaultValue) Children() []Expression {
if e == nil {
return nil
}
return []Expression{e.Expression}
}
// Eval implements sql.Expression
func (e *ColumnDefaultValue) Eval(ctx *Context, r Row) (interface{}, error) {
if e == nil {
return nil, nil
}
val, err := e.Expression.Eval(ctx, r)
if err != nil {
return nil, err
}
if val == nil && !e.returnNil {
return nil, ErrColumnDefaultReturnedNull.New()
}
if e.outType != nil {
if val, err = e.outType.Convert(val); err != nil {
return nil, ErrIncompatibleDefaultType.New()
}
}
return val, nil
}
// IsLiteral returns whether this expression represents a literal default value (otherwise it's an expression default value).
func (e *ColumnDefaultValue) IsLiteral() bool {
if e == nil {
return true // we return the literal nil, hence true
}
return e.literal
}
// IsParenthesized returns whether this column default was specified in parentheses, using the expression default value form.
// It is almost always the opposite of IsLiteral, but there is one edge case where matching MySQL's behavior require that
// we can distinguish between a non-literal value in parens and a non-literal value not in parens. The edge case is using
// now/current_timestamp as a column default; now/current_timestamp can be specified without parens for datetime/timestamp
// fields, but it must be enclosed in parens to be used as the default for other types.
func (e *ColumnDefaultValue) IsParenthesized() bool {
if e == nil {
return false // we return the literal nil, hence false
}
return e.parenthesized
}
// IsNullable implements sql.Expression
func (e *ColumnDefaultValue) IsNullable() bool {
if e == nil {
return true
}
if !e.returnNil {
return false
}
return e.Expression.IsNullable()
}
// Resolved implements sql.Expression
func (e *ColumnDefaultValue) Resolved() bool {
if e == nil {
return true
}
if e.outType == nil {
return false
}
return e.Expression.Resolved()
}
// String implements sql.Expression
func (e *ColumnDefaultValue) String() string {
//TODO: currently (2+2)/2 will, when output as a string, give (2 + 2 / 2), which is clearly wrong
if e == nil {
return ""
}
// https://dev.mysql.com/doc/refman/8.0/en/data-type-defaults.html
// The default value specified in a DEFAULT clause can be a literal constant or an expression. With one exception,
// enclose expression default values within parentheses to distinguish them from literal constant default values.
if e.literal {
return e.Expression.String()
} else {
return fmt.Sprintf("(%s)", e.Expression.String())
}
}
func (e *ColumnDefaultValue) DebugString() string {
if e == nil {
return ""
}
if e.literal {
return DebugString(e.Expression)
} else if e.parenthesized {
return fmt.Sprintf("parenthesized(%s)", DebugString(e.Expression))
} else {
return fmt.Sprintf("(%s)", DebugString(e.Expression))
}
}
// Type implements sql.Expression
func (e *ColumnDefaultValue) Type() Type {
if e == nil {
return nil
}
if e.outType == nil {
return e.Expression.Type()
}
return e.outType
}
// WithChildren implements sql.Expression
func (e *ColumnDefaultValue) WithChildren(children ...Expression) (Expression, error) {
if e == nil && len(children) == 0 {
return e, nil
}
if len(children) != 1 {
return nil, ErrInvalidChildrenNumber.New(e, len(children), 1)
}
if e == nil {
isLiteral := len(children[0].Children()) == 0 //impossible to know, best guess
return NewColumnDefaultValue(children[0], e.outType, isLiteral, !isLiteral, true)
} else {
return NewColumnDefaultValue(children[0], e.outType, e.literal, e.parenthesized, e.returnNil)
}
}
// CheckType validates that the ColumnDefaultValue has the correct type.
func (e *ColumnDefaultValue) CheckType(ctx *Context) error {
if e.outType != nil && e.literal {
val, err := e.Expression.Eval(ctx, nil)
if err != nil {
return err
}
if val == nil && !e.returnNil {
return ErrIncompatibleDefaultType.New()
}
_, err = e.outType.Convert(val)
if err != nil {
return ErrIncompatibleDefaultType.Wrap(err)
}
}
return nil
}
type UnresolvedColumnDefault struct {
exprString string
}
func (u UnresolvedColumnDefault) Resolved() bool {
return false
}
func (u UnresolvedColumnDefault) String() string {
return u.exprString
}
func (u UnresolvedColumnDefault) Type() Type {
panic("UnresolvedColumnDefault is a placeholder node, but Type() was called")
}
func (u UnresolvedColumnDefault) IsNullable() bool {
return true
}
func (u UnresolvedColumnDefault) Eval(ctx *Context, row Row) (interface{}, error) {
panic("UnresolvedColumnDefault is a placeholder node, but Eval() was called")
}
func (u UnresolvedColumnDefault) Children() []Expression {
return nil
}
func (u UnresolvedColumnDefault) WithChildren(children ...Expression) (Expression, error) {
if len(children) != 0 {
return nil, ErrInvalidChildrenNumber.New(u, len(children), 0)
}
return u, nil
}