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<td align="center" valign="middle" class="til"><h3> sql基本语句 </h3>
发布时间：2007-05-23 来源：本站 作者：佚名<br />
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</table><p>1.If...Else...语句<br />格式：<br />If 布尔表达式<br /> {SQL语句或语句块}<br /> [Else<br /> {SQL语句或语句块}]<br />2.BEGIN...END语句<br />功能：将多条SQL语句封装起来，构成一个语句块<br />格式：<br />BEGIN<br /> {sql语句或语句块}<br />ENd<br />3.WHERE、BREAK、CONTINUE语句<br />[例]：求1到10之间的奇数数据和</p>
<pre>DECLARE @I smallint,@sum smallint
SELECT @i=0,@sum=0
WHILE @i>=0
BEGIN
SELECT @i=@i+1
IF @i>10
BREAK
If(@i%2)=0
CONTINUE
ELSE
SELECT @sum=@sum+@I
End
SELECT @sum</pre>
<p>4.WAITFOR语句<br />格式：WAITFOR{DELAY 'time'|TIME 'time'}<br />time:detetime<br />[例]：<br />WAITFOR TIME '10:00' 设置在10:00执行一次命令；<br />WAITFOR DELAY '1:00' 设置在一小时后执行一次命令。<br />5.RETURN([整数表达式])</p>
<p>CASE 表达式<br />(1)简单case表达式<br />CASE 表达式<br />WHEN 表达式1 THEN 表达式2<br />[WHEN 表达式3 THEN 表达式4[......]]<br />[ELSE 表达式N]<br />END<br />例：</p>
<pre>select name=convert(varchar(15),au_lname),
contract=case contract
when 0 then 'invalid contract.'
when 1 then 'valid contract.'
End
from authors</pre>
<p>(2)搜索型CASE表达式<br />CASE表达式<br />WHEN 布尔表达式1 THEN 表达式1<br />[WHEN 布尔表达式2 THEN 表达式2[.....]]<br />[ELSE 表达式N]<br />End<br /></p>
<pre>例：
select name=convert(varchar(15),au_lname),
contract=case contract
when cintract=0 then 'invalid contract.'
when contract<>0 then 'valid contract.'
End
from authors</pre>
<p> </p>
(3)CASE关系函数<br />CASE关系函数有以下3种形式：<br />●COALESCE(表达式1，表达式2）<br />●COALESCE(表达式1，表达式2,......,表达式N）<br />●NULLIF(表达式1，表达式2)<center><br /><script src="/js1/4682.js"></script></center>
<p>上一篇：<a href='/data/SQLServer/jc/200705/1183.htm'>sql的日期函数</a> 下一篇：<a href='/data/SQLServer/jc/200705/1185.htm'>sql的变量和运算符</a> </p></td>
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