github.com/dolthub/go-mysql-server@v0.18.0/sql/planbuilder/parse_column_default.go (about)

     1  // Copyright 2023 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package planbuilder
    16  
    17  import (
    18  	"fmt"
    19  	"strings"
    20  
    21  	"github.com/dolthub/vitess/go/vt/sqlparser"
    22  
    23  	"github.com/dolthub/go-mysql-server/sql"
    24  	"github.com/dolthub/go-mysql-server/sql/expression"
    25  	"github.com/dolthub/go-mysql-server/sql/plan"
    26  )
    27  
    28  // StringToColumnDefaultValue takes in a string representing a default value and returns the equivalent Expression.
    29  func StringToColumnDefaultValue(ctx *sql.Context, exprStr string) (*sql.ColumnDefaultValue, error) {
    30  	// all valid default expressions will parse correctly with SELECT prepended, as the parser will not parse raw expressions
    31  	stmt, err := sqlparser.Parse("SELECT " + exprStr)
    32  	if err != nil {
    33  		return nil, err
    34  	}
    35  	parserSelect, ok := stmt.(*sqlparser.Select)
    36  	if !ok {
    37  		return nil, fmt.Errorf("DefaultStringToExpression expected sqlparser.Select but received %T", stmt)
    38  	}
    39  	if len(parserSelect.SelectExprs) != 1 {
    40  		return nil, fmt.Errorf("default string does not have only one expression")
    41  	}
    42  	aliasedExpr, ok := parserSelect.SelectExprs[0].(*sqlparser.AliasedExpr)
    43  	if !ok {
    44  		return nil, fmt.Errorf("DefaultStringToExpression expected *sqlparser.AliasedExpr but received %T", parserSelect.SelectExprs[0])
    45  	}
    46  	proj, err := Parse(ctx, nil, fmt.Sprintf("SELECT %s", aliasedExpr.Expr))
    47  	if err != nil {
    48  		return nil, err
    49  	}
    50  	parsedExpr := proj.(*plan.Project).Projections[0]
    51  	if a, ok := parsedExpr.(*expression.Alias); ok {
    52  		parsedExpr = a.Child
    53  	}
    54  	_, isParenthesized := aliasedExpr.Expr.(*sqlparser.ParenExpr)
    55  
    56  	var isLiteral bool
    57  	switch e := parsedExpr.(type) {
    58  	case *expression.UnaryMinus:
    59  		_, isLiteral = e.Child.(*expression.Literal)
    60  	case *expression.UnresolvedFunction:
    61  		isLiteral = false
    62  	default:
    63  		isLiteral = len(parsedExpr.Children()) == 0 && !strings.HasPrefix(exprStr, "(")
    64  	}
    65  	return ExpressionToColumnDefaultValue(parsedExpr, isLiteral, isParenthesized), nil
    66  }
    67  
    68  // MustStringToColumnDefaultValue is used for creating default values on tables that do not go through the analyzer. Does not handle
    69  // function nor column references.
    70  func MustStringToColumnDefaultValue(ctx *sql.Context, exprStr string, outType sql.Type, nullable bool) *sql.ColumnDefaultValue {
    71  	expr, err := StringToColumnDefaultValue(ctx, exprStr)
    72  	if err != nil {
    73  		panic(err)
    74  	}
    75  	expr, err = sql.NewColumnDefaultValue(expr.Expr, outType, expr.IsLiteral(), !expr.IsLiteral(), nullable)
    76  	if err != nil {
    77  		panic(err)
    78  	}
    79  	return expr
    80  }