下面先来看看例子：
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">table表
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">字段1字段2
idname
1a
2b
3c
4c
5b
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">库结构大概这样，这只是一个简单的例子，实际情况会复杂得多。
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">比如我想用一条语句查询得到name不重复的所有数据，那就必须
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">使用distinct去掉多余的重复记录。
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">select distinct name from table
得到的结果是:
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">----------
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">name
ac
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">好像达到效果了，可是，我想要得到的是id值呢？改一下查询语句吧:
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">select distinct name,id from table
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">结果会是:
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">----------
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">id name
1 a
2 b
3 c
4 c
5 b
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">distinct怎么没起作用？作用是起了的，不过他同时作用了两个
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">字段，也就是必须得id与name都相同的才会被排除
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">我们再改改查询语句:
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">select id,distinct name from table
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">很遗憾，除了错误信息你什么也得不到，distinct必须放在开头。难到不能把distinct放到where条件里？能，照样报错。
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">--------------------------------------------------------
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">下面方法可行:
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">select *,count(distinct name) from table group by name
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">结果:
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">id name count(distinct name)
1 a 1
2 b 1
3 c 1
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">最后一项是多余的，不用管就行了，目的达到
<P style="BORDER-TOP-WIDTH: 0px; PADDING-RIGHT: 0px; PADDING-LEFT: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; PADDING-BOTTOM: 0px; MARGIN: 0px 0px 5px; WORD-BREAK: normal; LINE-HEIGHT: 1.5em; PADDING-TOP: 0px; LIST-STYLE-TYPE: none; BORDER-RIGHT-WIDTH: 0px; WORD-WRAP: normal">group by 必须放在 order by 和 limit之前，不然会报错
<DIV id=c_jquery_test style="DISPLAY: none">
