code: func RewriteSimpleExprWithSchema(ctx sessionctx.Context, expr ast.ExprNode, schema *Schema) (Expression, error) {
  	rewriter := &simpleRewriter{ctx: ctx, schema: schema}
  	expr.Accept(rewriter)
  	if rewriter.err != nil {
  		return nil, rewriter.err
  	}
  	return rewriter.pop(), nil
  }
docs: // RewriteSimpleExprWithSchema rewrites simple ast.ExprNode to expression.Expression.