<select id="selectById" resultType="Zhai">
SELECT * FROM ZHAI
WHERE
<if test="a != null">
a LIKE #{a}
</if>
<if test="b != null">
AND b LIKE #{b}
</if>
</select>
SELECT * FROM ZHAI WHERE AND b LIKE 'b'
<select id="selectById" resultType="Zhai">
SELECT * FROM ZHAI
WHERE 1 = 1
<if test="a != null">
AND a LIKE #{a}
</if>
<if test="b != null">
AND b LIKE #{b}
</if>
</select>
<select id="selectById" resultType="Zhai">
SELECT * FROM ZHAI
<where>
<trim prefixOverrides="and">
<if test="a != null">
AND a LIKE #{a}
</if>
<if test="b != null">
AND b LIKE #{b}
</if>
</trim>
</where>
</select>