sql有转换字符串为数值的函数，先调用那个，再sum

/*
 Navicat Premium Data Transfer

 Source Server         : LocalDB
 Source Server Type    : SQL Server
 Source Server Version : 13004001
 Source Host           : (LocalDB)\MSSQLLocalDB:1433
 Source Catalog        : BookStore
 Source Schema         : dbo

 Target Server Type    : SQL Server
 Target Server Version : 13004001
 File Encoding         : 65001

 Date: 06/12/2019 14:21:12
*/


-- ----------------------------
-- Table structure for test
-- ----------------------------
IF EXISTS (SELECT * FROM sys.all_objects WHERE object_id = OBJECT_ID(N'[dbo].[test]') AND type IN ('U'))
    DROP TABLE [dbo].[test]
GO

CREATE TABLE [dbo].[test] (
  [Id] int  NOT NULL,
  [TextVal] varchar(255) COLLATE SQL_Latin1_General_CP1_CI_AS  NULL
)
GO
-- ----------------------------
-- Records of test
-- ----------------------------
INSERT INTO [dbo].[test] VALUES (N'1', N'1')
GO

INSERT INTO [dbo].[test] VALUES (N'2', N'1.1')
GO

INSERT INTO [dbo].[test] VALUES (N'3', NULL)
GO

INSERT INTO [dbo].[test] VALUES (N'4', N'1.33')
GO


SELECT sum(case when t.TextVal= '' then 0 else CAST (  t.TextVal AS NUMERIC(10,2) ) end )
from test t

把你的sum（ZJM）更换为sum(case when ZJM= '' then 0 else CAST ( ZJM AS NUMERIC(10,2) )