MYSQL mybatis

1 每个语句的结束记得加分号;

3 is null, is not null 用于判断某个字段或是变量为null或不为null.

4 isnull(expr) 的用法：
　　如expr 为null，那么isnull() 的返回值为 1，否则返回值为 0。 

5 ifnull(exp1,exp2)如果exp1是null的话，就用exp2的值，否则还是用exp1的值

6 NULLIF(expr1,expr2)    如果expr1 =   expr2     成立，那么返回值为NULL，否则返回值为   expr1

7 out参数,存储过程的参数要指明in,out。在调用存储过程时，用带@开头的变量来接值，比如 call procedure1(1,1,@result);

8 用户变量不用声明，直接在变量前加@就可用

9 select count(distinct id) as rowCount from table1

10 Mysql数据库里表名大小写敏感，字段名大小写不敏感，sql server里大小写不敏感

myBatis动态构建sql语句

if

<if test="state != null">
         state = #{state}
</if> 

choose when otherwise,不想写太多 条件语句的时候，可以用这个

<select id="findActiveBlogLike"
     resultType="Blog">
  SELECT * FROM BLOG WHERE state = ‘ACTIVE’
  <choose>
    <when test="title != null">
      AND title like #{title}
    </when>
    <when test="author != null and author.name != null">
      AND author_name like #{author.name}
    </when>
    <otherwise>
      AND featured = 1
    </otherwise>
  </choose>
</select>

where, 会自动去掉多余的and 或or

<select id="findActiveBlogLike"
     resultType="Blog">
  SELECT * FROM BLOG 
  <where> 
    <if test="state != null">
         state = #{state}
    </if> 
    <if test="title != null">
        AND title like #{title}
    </if>
    <if test="author != null and author.name != null">
        AND author_name like #{author.name}
    </if>
  </where>
</select>

trim ,显示的去掉字符

<trim prefix="WHERE" prefixOverrides="AND |OR ">
  ... 
</trim>

set，会自动去掉多余的逗号

<update id="updateAuthorIfNecessary">
  update Author
    <set>
      <if test="username != null">username=#{username},</if>
      <if test="password != null">password=#{password},</if>
      <if test="email != null">email=#{email},</if>
      <if test="bio != null">bio=#{bio}，</if>
    </set>
  where id=#{id}
</update>

foreach

<foreach item="item" index="index" collection="list"
      open="(" separator="," close=")">
        #{item}
  </foreach>

bind

<select id="selectBlogsLike" resultType="Blog">
  <bind name="pattern" value="‘%‘ + _parameter.getTitle() + ‘%‘" />
  SELECT * FROM BLOG
  WHERE title LIKE #{pattern}
</select>

mybatis里所有的判断都是用test  =""，比如test="username != null"

mybatis调用存储过程

 <!-- 创建多个文档 -->
    <select id="createProcedures" parameterType="map" >
	    <foreach collection="entities" item="entity" index="index" >
	    call SP_CREATE_PROCEDURE(
		#{entity.fileName, mode=IN, jdbcType=VARCHAR},
		#{entity.filePath, mode=IN, jdbcType=VARCHAR},
		#{entity.deviceIdsWithComma, mode=IN, jdbcType=VARCHAR},
		#{entity.createUserId, mode=IN, jdbcType=VARCHAR}
		);
	    </foreach>
    </select>

myBatis JDBC type和java数据类型对应表：

 <resultMap id="bookMapping" type="com.expample.base.repository.entity.BookEntity">
        <result property="id" column="Id"/>
        <result property="Name" column="Name"/>
        <result property="filePath" column="FilePath"/>
        <result property="createUserName" column="CreateUserName"/>
        <result property="createUserId" column="CreateUserId"/>
        <result property="createTime" column="CreateTime"/>
        <result property="isPublished" column="IsPublished"/>
        <collection property="assDevices" ofType="com.expample.base.repository.entity.BookCategoryAssEntity">
            <result property="id" column="CateotryID"/>
            <result property="name" column="CateotryName"/>
        </collection>
    </resultMap>
 <select id="getBookById"  parameterType="Integer" resultMap="bookMapping">
       SELECT
	    B.Id,
            B.Name,
            B.FilePath,
            E.Name as CreateUserName,
            E.Code as Code,
            B.CreateUserId,
            B.CreateTime,
            B.IsPublished,
            C.ID as CateotryID,
            C.Name as CateotryName
       FROM `Book` AS B
       LEFT JOIN `BookCategoryAss`AS BC on B.Id = BC.ProcedureId
       LEFT JOIN `Employee` AS E ON ON B.CreateUserId = E.Id 
       LEFT JOIN `Category` AS C ON BC.Category.Id = C.Id 
       WHERE B.id = #{id}
    </select>

　　mybatis语法，从数据库查出来的字段可以多于或少于resultType指定的类的属性，都会按能对应的上的名字进行映射。

MYSQL mybatis

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