我就廢話不多說了，大家還是直接看代碼吧~
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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參數為空時，最終生成SQL語句為
SELECT * FROM BLOG
WHERE
執行會出錯，當然，你可以在where 后加一個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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但是這個做法不太“環保”（畢竟引入了一個垃圾條件），其實只要改成<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
>
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