vitess.io/vitess@v0.16.2/go/vt/vtgate/planbuilder/operators/expressions.go (about)

     1  /*
     2  Copyright 2022 The Vitess Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package operators
    18  
    19  import (
    20  	"vitess.io/vitess/go/vt/sqlparser"
    21  	"vitess.io/vitess/go/vt/vterrors"
    22  	"vitess.io/vitess/go/vt/vtgate/planbuilder/plancontext"
    23  	"vitess.io/vitess/go/vt/vtgate/semantics"
    24  )
    25  
    26  // BreakExpressionInLHSandRHS takes an expression and
    27  // extracts the parts that are coming from one of the sides into `ColName`s that are needed
    28  func BreakExpressionInLHSandRHS(
    29  	ctx *plancontext.PlanningContext,
    30  	expr sqlparser.Expr,
    31  	lhs semantics.TableSet,
    32  ) (bvNames []string, columns []*sqlparser.ColName, rewrittenExpr sqlparser.Expr, err error) {
    33  	rewrittenExpr = sqlparser.CopyOnRewrite(expr, nil, func(cursor *sqlparser.CopyOnWriteCursor) {
    34  		node, ok := cursor.Node().(*sqlparser.ColName)
    35  		if !ok {
    36  			return
    37  		}
    38  		deps := ctx.SemTable.RecursiveDeps(node)
    39  		if deps.IsEmpty() {
    40  			err = vterrors.VT13001("unknown column. has the AST been copied?")
    41  			cursor.StopTreeWalk()
    42  			return
    43  		}
    44  		if !deps.IsSolvedBy(lhs) {
    45  			return
    46  		}
    47  
    48  		node.Qualifier.Qualifier = sqlparser.NewIdentifierCS("")
    49  		columns = append(columns, node)
    50  		bvName := node.CompliantName()
    51  		bvNames = append(bvNames, bvName)
    52  		arg := sqlparser.NewArgument(bvName)
    53  		// we are replacing one of the sides of the comparison with an argument,
    54  		// but we don't want to lose the type information we have, so we copy it over
    55  		ctx.SemTable.CopyExprInfo(node, arg)
    56  		cursor.Replace(arg)
    57  	}, nil).(sqlparser.Expr)
    58  
    59  	if err != nil {
    60  		return nil, nil, nil, err
    61  	}
    62  	ctx.JoinPredicates[expr] = append(ctx.JoinPredicates[expr], rewrittenExpr)
    63  	return
    64  }