动态sql（where标签）

where标签就是为sql加上where关键字，且会自动的多余的and、or关键字，当所有的条件都不成立的时候，where标签也不会生成

<select id="getEmp" resultType="com.simple.simple1.Emp">
    select * from t_user where 
    <if test="username!= null and username != ''">
        username = #{username}
    </if>
    <if test="password!= null and password != ''">
        and password = #{password}
    </if>
    <if test="age!= null and age != ''">
        and age = #{age}
    </if>
    <if test="sex!= null and sex != ''">
        and sex = #{sex}
    </if>
    <if test="email!= null and email != ''">
        and email = #{email}
    </if>
</select>

标签：username,标签,sex,sql,where,email
来源： https://www.cnblogs.com/new228666/p/16418447.html