javaweb之条件查询和多表联合查询

条件查询

public List<Bill> findListBy(Map<String,Object> maps) throws Exception{
        //where a.productName like concat('%',?,'%') and totalPrice>=? and totalPrice<=?

        List<Bill> billList = new ArrayList<>();
        String sql = "select a.id,a.billCode,a.productName,a.productCount,\n" +
                "a.productUnit,a.productDesc,a.totalPrice,a.providerId,b.proName " +
                " from smbms_bill a left join smbms_provider b on a.providerId=b.id " +
                "where 1=1 ";
        List<Object> params = new ArrayList<>();

        if(maps.get("pName")!=null){
            sql += " and a.productName like concat('%',?,'%')";
            params.add(maps.get("pName"));
        }
        if(maps.get("begin")!=null){
            sql+= "and totalPrice>=?";
            params.add(maps.get("begin"));
        }
        System.out.println("maps.get(\"end\")===="+maps.get("end"));
        if(maps.get("end")!=null){
            sql+= "and totalPrice<=?";
            params.add(maps.get("end"));
        }
        ResultSet rs = query(sql,params);
        while(rs.next()){
            Bill bill = new Bill();
            bill.setId(rs.getInt("id"));
            bill.setBillCode(rs.getString("billCode"));
            bill.setProductName(rs.getString("productName"));
            bill.setProductCount(rs.getInt("productCount"));
            bill.setProductUnit(rs.getString("productUnit"));
            bill.setProductDesc(rs.getString("productDesc"));
            bill.setTotalPrice(rs.getBigDecimal("totalPrice"));

            Provider provider = new Provider();
            provider.setId(rs.getInt("providerId"));
            provider.setProName(rs.getString("proName"));

            bill.setProvider(provider);


            billList.add(bill);
        }
        return billList;
    }

工具类封装

import java.util.ArrayList;
import java.util.List;

public class DynamicSqlBuilder {
    private final StringBuilder sqlBuilder;
    private final List<Object> params;
    private boolean whereAdded = false;

    public DynamicSqlBuilder(String baseSql) {
        this.sqlBuilder = new StringBuilder(baseSql);
        this.params = new ArrayList<>();
    }

    /**
     * 添加等于条件（=）
     * @param column 数据库字段名
     * @param value 条件值
     */
    public DynamicSqlBuilder eq(String column, Object value) {
        addCondition(column, value, " = ?");
        return this;
    }

    /**
     * 添加模糊查询条件（LIKE）
     * @param column 数据库字段名
     * @param value 条件值
     */
    public DynamicSqlBuilder like(String column, String value) {
        if (value != null && !value.isEmpty()) {
            addCondition(column, "%" + value + "%", " LIKE ?");
        }
        return this;
    }

    /**
     * 添加大于条件（>）
     * @param column 数据库字段名
     * @param value 条件值
     */
    public DynamicSqlBuilder gt(String column, Object value) {
        addCondition(column, value, " > ?");
        return this;
    }

    /**
     * 添加IN条件（IN）
     * @param column 数据库字段名
     * @param values 值列表
     */
    public DynamicSqlBuilder in(String column, List<?> values) {
        if (values != null && !values.isEmpty()) {
            addWhereClause();
            sqlBuilder.append(column).append(" IN (");
            for (int i = 0; i < values.size(); i++) {
                sqlBuilder.append(i > 0 ? ",?" : "?");
                params.add(values.get(i));
            }
            sqlBuilder.append(")");
        }
        return this;
    }

    // 核心条件拼接逻辑
    private void addCondition(String column, Object value, String operator) {
        if (value != null && !(value instanceof String && ((String) value).isEmpty())) {
            addWhereClause();
            sqlBuilder.append(column).append(operator);
            params.add(value);
        }
    }

    // 动态添加WHERE关键字
    private void addWhereClause() {
        if (!whereAdded) {
            sqlBuilder.append(" WHERE ");
            whereAdded = true;
        } else {
            sqlBuilder.append(" AND ");
        }
    }

    /**
     * 构建最终SQL和参数
     * @return 包含SQL字符串和参数数组的对象
     */
    public SqlResult build() {
        return new SqlResult(sqlBuilder.toString(), params.toArray());
    }

    // 返回结果封装类
    public static class SqlResult {
        private final String sql;
        private final Object[] params;

        public SqlResult(String sql, Object[] params) {
            this.sql = sql;
            this.params = params;
        }

        public String getSql() {
            return sql;
        }

        public Object[] getParams() {
            return params;
        }
    }
}

使用1

public class TestDemo {
    public static void main(String[] args) {
        // 1. 基础SQL（必须包含SELECT和FROM）
        String baseSql = "SELECT * FROM users";
        
        // 2. 动态构建条件
        DynamicSqlBuilder builder = new DynamicSqlBuilder(baseSql)
            .eq("status", 1)                      // 状态为1
            .like("name", "张")                    // 名字包含"张"
            .gt("age", 18)                        // 年龄大于18
            .in("department_id", List.of(101, 203)); // 部门ID在列表中
        
        // 3. 获取结果
        DynamicSqlBuilder.SqlResult result = builder.build();
        
        // 4. 输出结果
        System.out.println("完整SQL: " + result.getSql());
        System.out.println("参数数组: " + Arrays.toString(result.getParams()));
    }
}

使用2

@Test
    public void test01(){
        String name = "张三";
        String pwd = null;
        String add = "龙鳞路";
        DynamicSqlBuilder dynamicSqlBuilder = new DynamicSqlBuilder("SELECT * FROM users");
        dynamicSqlBuilder.eq("name", name);
        dynamicSqlBuilder.eq("pwd", pwd);
        dynamicSqlBuilder.eq("add", add);
        DynamicSqlBuilder.SqlResult result = dynamicSqlBuilder.build();
        System.out.println(result.getSql());
        Object[] objects = result.getParams();
        for (Object obj:objects){
            System.out.println(obj);
        }

    }

完整SQL: SELECT * FROM users WHERE status = ? AND name LIKE ? AND age > ? AND department_id IN (?,?)
参数数组: [1, "%张%", 18, 101, 203]

 核心特性
​​智能条件拼接​​
自动跳过null或空字符串条件 
首次添加条件时自动插入WHERE关键字，后续条件用AND连接
支持=、LIKE、>、IN等常用操作符
​​防SQL注入设计​​
所有值通过?占位符处理
参数值独立存储在Object[]数组，符合预编译规范 
​​链式调用​​
采用builder.eq(...).like(...)的流畅接口风格
类似MyBatis-Plus的Wrapper写法 
​​IN语句优化​​
自动展开List为(?,?,?)格式
支持任意类型的集合参数

使用条件

必须提供基础SQL

// 正确示例
new DynamicSqlBuilder("SELECT id,name FROM user")

// 错误示例（缺少SELECT/FROM）
new DynamicSqlBuilder("user")

空值处理规则​​

字符串：跳过null和""
数字：跳过null
集合：跳过null和空集合

​​特殊字符转义

​​特殊字符转义​​如果参数包含%或_等特殊字符，需在调用前转义

.like("name", "100%".replace("%", "\\%"))

多表联合查询

一对一

public List<Bill> findListBy(Map<String,Object> maps) throws Exception{
List<Bill> billList = new ArrayList<>();
ResultSet rs = query(sql,params);
while(rs.next()){
        Bill bill = new Bill();
        bill.setId(rs.getInt("id"));
        bill.setBillCode(rs.getString("billCode"));
        bill.setProductName(rs.getString("productName"));
        bill.setProductCount(rs.getInt("productCount"));
        bill.setProductUnit(rs.getString("productUnit"));
        bill.setProductDesc(rs.getString("productDesc"));
        bill.setTotalPrice(rs.getBigDecimal("totalPrice"));

        Provider provider = new Provider();
        provider.setId(rs.getInt("providerId"));
        provider.setProName(rs.getString("proName"));

        bill.setProvider(provider);


        billList.add(bill);
    }
    return billList;
}

一对多

public class ProviderDaoImpl extends BaseDao implements ProviderDao, BaseInterface<Provider> {
    @Override
    public Provider findProviderById(Integer id)  throws Exception{
        String sql = "select id,proName from smbms_provider where id=?";
        String billSql = "select id,billCode from smbms_bill where prividerId=?";
        Provider provider = null;
        ResultSet rs = query(sql,null);
        while (rs.next()){
            provider = new Provider();
            provider.setId(rs.getInt("id"));
            provider.setProName(rs.getString("proName"));
            ResultSet resultSet = query(billSql,null);
            List<Bill> billList = new ArrayList<>();
            while(resultSet.next()){
                Bill bill = new Bill();
                bill.setId(rs.getInt("id"));
                bill.setBillCode(rs.getString("billCode"));
                billList.add(bill);
            }

            provider.setList(billList);

        }
        return provider;
    }