forked from dolthub/go-mysql-server
/
coalesce.go
132 lines (111 loc) · 3.21 KB
/
coalesce.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"
"strings"
"github.com/gabereiser/go-mysql-server/sql"
)
// Coalesce returns the first non-NULL value in the list, or NULL if there are no non-NULL values.
type Coalesce struct {
args []sql.Expression
}
var _ sql.FunctionExpression = (*Coalesce)(nil)
// NewCoalesce creates a new Coalesce sql.Expression.
func NewCoalesce(args ...sql.Expression) (sql.Expression, error) {
if len(args) == 0 {
return nil, sql.ErrInvalidArgumentNumber.New("COALESCE", "1 or more", 0)
}
return &Coalesce{args}, nil
}
// FunctionName implements sql.FunctionExpression
func (c *Coalesce) FunctionName() string {
return "coalesce"
}
// Description implements sql.FunctionExpression
func (c *Coalesce) Description() string {
return "returns the first non-null value in a list."
}
// Type implements the sql.Expression interface.
// The return type of Type() is the aggregated type of the argument types.
func (c *Coalesce) Type() sql.Type {
for _, arg := range c.args {
if arg == nil {
continue
}
t := arg.Type()
if t == nil {
continue
}
return t
}
return nil
}
// IsNullable implements the sql.Expression interface.
// Returns true if all arguments are nil
// or of the first non-nil argument is nullable, otherwise false.
func (c *Coalesce) IsNullable() bool {
for _, arg := range c.args {
if arg == nil {
continue
}
return arg.IsNullable()
}
return true
}
func (c *Coalesce) String() string {
var args = make([]string, len(c.args))
for i, arg := range c.args {
args[i] = arg.String()
}
return fmt.Sprintf("%s(%s)", c.FunctionName(), strings.Join(args, ","))
}
// WithChildren implements the Expression interface.
func (*Coalesce) WithChildren(children ...sql.Expression) (sql.Expression, error) {
return NewCoalesce(children...)
}
// Resolved implements the sql.Expression interface.
// The function checks if first non-nil argument is resolved.
func (c *Coalesce) Resolved() bool {
for _, arg := range c.args {
if arg == nil {
continue
}
if !arg.Resolved() {
return false
}
}
return true
}
// Children implements the sql.Expression interface.
func (c *Coalesce) Children() []sql.Expression { return c.args }
// Eval implements the sql.Expression interface.
// The function evaluates the first non-nil argument. If the value is nil,
// then we keep going, otherwise we return the first non-nil value.
func (c *Coalesce) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
for _, arg := range c.args {
if arg == nil {
continue
}
val, err := arg.Eval(ctx, row)
if err != nil {
return nil, err
}
if val == nil {
continue
}
return val, nil
}
return nil, nil
}