/
nullif.go
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/
nullif.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 function
import (
"fmt"
"github.com/dolthub/go-mysql-server/sql"
"github.com/dolthub/go-mysql-server/sql/expression"
"github.com/dolthub/go-mysql-server/sql/types"
)
// NullIf function compares two expressions and returns NULL if they are equal. Otherwise, the first expression is returned.
type NullIf struct {
expression.BinaryExpressionStub
}
var _ sql.FunctionExpression = (*NullIf)(nil)
var _ sql.CollationCoercible = (*NullIf)(nil)
// NewNullIf returns a new NULLIF UDF
func NewNullIf(ex1, ex2 sql.Expression) sql.Expression {
return &NullIf{
expression.BinaryExpressionStub{
LeftChild: ex1,
RightChild: ex2,
},
}
}
// FunctionName implements sql.FunctionExpression
func (f *NullIf) FunctionName() string {
return "nullif"
}
// Description implements sql.FunctionExpression
func (f *NullIf) Description() string {
return "returns NULL if expr1 = expr2 is true, otherwise returns expr1."
}
// Eval implements the Expression interface.
func (f *NullIf) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
if types.IsNull(f.LeftChild) && types.IsNull(f.RightChild) {
return nil, nil
}
val, err := expression.NewEquals(f.LeftChild, f.RightChild).Eval(ctx, row)
if err != nil {
return nil, err
}
if b, ok := val.(bool); ok && b {
return nil, nil
}
return f.LeftChild.Eval(ctx, row)
}
// Type implements the Expression interface.
func (f *NullIf) Type() sql.Type {
if types.IsNull(f.LeftChild) {
return types.Null
}
return f.LeftChild.Type()
}
// CollationCoercibility implements the interface sql.CollationCoercible.
func (f *NullIf) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
if types.IsNull(f.LeftChild) {
return sql.Collation_binary, 6
}
return sql.GetCoercibility(ctx, f.LeftChild)
}
// IsNullable implements the Expression interface.
func (f *NullIf) IsNullable() bool {
return true
}
func (f *NullIf) String() string {
return fmt.Sprintf("%s(%s,%s)", f.FunctionName(), f.LeftChild, f.RightChild)
}
// WithChildren implements the Expression interface.
func (f *NullIf) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 2 {
return nil, sql.ErrInvalidChildrenNumber.New(f, len(children), 2)
}
return NewNullIf(children[0], children[1]), nil
}