我就废话不多说了，大家还是直接看代码吧~
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<
select
id
=
"findActiveBlogLike"
resultType
=
"Blog"
>
SELECT * FROM BLOG
WHERE
<
if
test
=
"state != null"
>
state = #{state}
</
if
>
</
select
>
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如果state参数为空时，最终生成SQL语句为
SELECT * FROM BLOG
WHERE
执行会出错，当然，你可以在where 后加一个1=1，改成
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<
select
id
=
"findActiveBlogLike"
resultType
=
"Blog"
>
SELECT * FROM BLOG
WHERE 1=1
<
if
test
=
"state != null"
>
and state = #{state}
</
if
>
</
select
>
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但是这个做法不太“环保”（毕竟引入了一个垃圾条件），其实只要改成<where>...</where>即可
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<
select
id
=
"findActiveBlogLike"
resultType
=
"Blog"
>
SELECT * FROM BLOG
<
where
>
<
if
test
=
"state != null"
>
and state = #{state}
</
if
>
</
where
>
</
select
>
|