Mybatis中and和or的細節處理

當一條SQL中既有條件查又有模糊查的時候，偶爾會遇到這樣的and拼接問題。參考如下代碼：

<select id="listSelectAllBusiness">
        select * from ***
        where 
        <if test="a!= null">
            a = #{a}
        </if>
        <if test="b!= null">
            and b in
            <foreach collection="list" index="index" item="item" open="(" separator="," close=")">
                #{item}
            </foreach>
        </if>
        <if test="c!= null">
            and name like '%${c}%' or code like '%${c}%'
        </if>
            order by id desc
            limit #{limit} offset #{page}
</select>

這樣寫的錯誤是如果a==null那么第二個條件中就會多一個and，語句會變成select * from *** where and b in (...)，而如果條件全都不滿足的話SQL會變成select * from *** where order by id desc limit...解決辦法：加上<where>標簽，如下：

<select id="listSelectAllBusiness">
        select * from ***
        <where> 
        <if test="a!= null">
            a = #{a}
        </if>
        <if test="b!= null">
            and b in
            <foreach collection="list" index="index" item="item" open="(" separator="," close=")">
                #{item}
            </foreach>
        </if>
        <if test="c!= null">
            and name like '%${c}%' or code like '%${c}%'
        </if>
        </where>
            order by id desc
            limit #{limit} offset #{page}
</select>

如上代碼所示，加上一個<where>標簽即可，where標簽會自動識別，如果前面條件不滿足的話，會自己去掉and。如果滿足的話會自己加上and。但是這句語句還是有問題，就是c條件里的語句里面有一個or，如果前面全部ab條件中有滿足的話就會形成這樣的SQL，select * from *** where a = ? and name like '%%' or code like '%%'，這條就類似SQL注入了，只要后面or條件滿足都能查出來，不滿足需求。解決辦法：給c條件的語句加上()，如下：

<select id="listSelectAllBusiness">
        select * from ***
        <where> 
        <if test="a!= null">
            a = #{a}
        </if>
        <if test="b!= null">
            and b in
            <foreach collection="list" index="index" item="item" open="(" separator="," close=")">
                #{item}
            </foreach>
        </if>
        <if test="c!= null">
            and (name like '%${c}%' or code like '%${c}%')
        </if>
        </where>
            order by id desc
            limit #{limit} offset #{page}
</select>