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j2eePDF格式的电子书

</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
FROM Player AS p, IN (p.teams) t 
WHERE <span style="font-weight: bold">t.league.sport</span> = &#39;soccer<span style="font-style: italic">&#39;</span><a name="wp80049"> </a>
</pre></div>
<a name="wp80051"> </a><h3 class="pHeading2">
WHERE Clause
</h3>
<a name="wp80053"> </a><p class="pBody">
The <code class="cCode">WHERE</code> clause specifies a conditional expression that limits the values returned by the query. The query returns all corresponding values in the data store for which the conditional expression is <code class="cCode">TRUE</code>. Although usually specified, the <code class="cCode">WHERE</code> clause is optional. If the <code class="cCode">WHERE</code> clause is omitted, then the query returns all values. The high-level syntax for the <code class="cCode">WHERE</code> clause follows:
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
where_clause ::= WHERE conditional_expression<a name="wp80054"> </a>
</pre></div>
<a name="wp80055"> </a><h4 class="pHeading3">
Literals
</h4>
<a name="wp80056"> </a><p class="pBody">
There are three kinds of literals: string, numeric, and boolean.
</p>
<a name="wp80057"> </a><h5 class="pHeading4">
String Literals
</h5>
<a name="wp80058"> </a><p class="pBody">
A string literal is enclosed in single quotes: 
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
&#39;Duke&#39;<a name="wp80059"> </a>
</pre></div>
<a name="wp80060"> </a><p class="pBody">
If a string literal contains a single quote, you indicate the quote with two single quotes:
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
&#39;Duke&#39;&#39;s&#39;<a name="wp80061"> </a>
</pre></div>
<a name="wp80062"> </a><p class="pBody">
Like a Java <code class="cCode">String</code>, a string literal in EJB QL uses the Unicode character encoding.
</p>
<a name="wp80063"> </a><h5 class="pHeading4">
Numeric Literals
</h5>
<a name="wp80064"> </a><p class="pBody">
There are two types of numeric literals: exact and approximate.
</p>
<a name="wp80065"> </a><p class="pBody">
An exact numeric literal is a numeric value without a decimal point, such as 65,<span style="font-family: Symbol"> -</span>233, <span style="font-family: Symbol">+</span>12. Using the Java integer syntax, exact numeric literals support numbers in the range of a Java <code class="cCode">long</code>.
</p>
<a name="wp80066"> </a><p class="pBody">
An approximate numeric literal is a numeric value in scientific notation, such as 57.,<span style="font-family: Symbol"> </span><span style="font-family: Symbol">-</span>85.7, <span style="font-family: Symbol">+</span>2.1. Using the syntax of the Java floating point literal, approximate numeric literals support numbers in the range of a Java <code class="cCode">double</code>.
</p>
<a name="wp80067"> </a><h5 class="pHeading4">
Boolean Literals
</h5>
<a name="wp80068"> </a><p class="pBody">
A boolean literal is either <code class="cCode">TRUE</code> or <code class="cCode">FALSE</code>. These keywords are not case sensitive.
</p>
<a name="wp80071"> </a><h4 class="pHeading3">
Input Parameters
</h4>
<a name="wp80072"> </a><p class="pBody">
An input parameter is designated by a question mark (<code class="cCode">?</code>) followed by an integer. For example, the first input parameter is <code class="cCode">?1</code>, the second is <code class="cCode">?2</code>, and so forth.
</p>
<a name="wp80073"> </a><p class="pBody">
The following rules apply to input parameters:
</p>
<div class="pSmartList1"><ul class="pSmartList1">
<a name="wp80074"> </a><div class="pSmartList1"><li>They can be used only in a <code class="cCode">WHERE</code> clause.</li></div>
<a name="wp80075"> </a><div class="pSmartList1"><li>Their use is restricted to a single-valued path expression within a conditional expression.</li></div>
<a name="wp80076"> </a><div class="pSmartList1"><li>They must be numbered, starting with the integer 1.</li></div>
<a name="wp80077"> </a><div class="pSmartList1"><li>The number of input parameters in the <code class="cCode">WHERE</code> clause must not exceed the number of input parameters in the corresponding finder or select method.</li></div>
<a name="wp80078"> </a><div class="pSmartList1"><li>The type of an input parameter in the <code class="cCode">WHERE</code> clause must match the type of the corresponding argument in the finder or select method.</li></div>
</ul></div>
<a name="wp80081"> </a><h4 class="pHeading3">
Conditional Expressions
</h4>
<a name="wp80082"> </a><p class="pBody">
A <code class="cCode">WHERE</code> clause consists of a conditional expression, which is evaluated from left to right within a precedence level. You may change the order of evaluation with parentheses.
</p>
<a name="wp80083"> </a><p class="pBody">
Here is the syntax of a conditional expression:
</p>
<a name="wp81121"> </a><p class="pBody">
conditional_expression ::= conditional_term |<br />    conditional_expression <code class="cCodeBold">OR</code> conditional_term<br /><br />conditional_term ::= conditional_factor | <br />    conditional_term <code class="cCodeBold">AND</code> conditional_factor<br /><br />conditional_factor ::= [<code class="cCodeBold">NOT</code> ] conditional_primary<br /><br />conditional_primary ::= simple_cond_expression |<br />     (conditional_expression)<br /><br />simple_cond_expression ::=<br />    comparison_expression | between_expression | <br />    like_expression | in_expression |<br />    null_comparison_expression |<br />    empty_collection_comparison_expression |<br />    collection_member_expression
</p>
<a name="wp80086"> </a><h4 class="pHeading3">
Operators and Their Precedence
</h4>
<a name="wp80125"> </a><p class="pBody">
<a  href="EJBQL5.html#wp80093">Table 24-2</a> lists the EJB QL operators in order of decreasing precedence.</p><div align="left">
<table border="1" summary="EJB QL Operator Precedence" id="wp80093">
  <caption><a name="wp80093"> </a><div class="pTableTitle">
Table 24-2   EJB QL Operator Precedence
</div>
</caption>
  <tr align="center">    <th><a name="wp80097"> </a><div class="pCellHeading">
 Type
</div>
</th>
    <th><a name="wp80099"> </a><div class="pCellHeading">
Precedence Order
</div>
</th>
</tr>
  <tr align="left">    <td><a name="wp80101"> </a><div class="pCellBody">
Navigation
</div>
</td>
    <td><a name="wp80103"> </a><div class="pCellBody">
<code class="cCode">. </code>(a period)
</div>
</td>
</tr>
  <tr align="left">    <td><a name="wp80105"> </a><div class="pCellBody">
Arithmetic<br /><br />
</div>
</td>
    <td><a name="wp80107"> </a><div class="pCellBody">
<code class="cCode">+ -</code> (unary)
</div>
<a name="wp80108"> </a><div class="pCellBody">
<code class="cCode">* /</code> (multiplication and division)
</div>
<a name="wp80109"> </a><div class="pCellBody">
+ - (addition and subtraction)
</div>
</td>
</tr>
  <tr align="left">    <td><a name="wp80111"> </a><div class="pCellBody">
Comparison<br /><br /><br /><br /><br />
</div>
</td>
    <td><a name="wp80113"> </a><div class="pCellBody">
<code class="cCode">=</code>
</div>
<a name="wp80114"> </a><div class="pCellBody">
<code class="cCode">&gt;</code>
</div>
<a name="wp80115"> </a><div class="pCellBody">
<code class="cCode">&gt;=</code>
</div>
<a name="wp80116"> </a><div class="pCellBody">
<code class="cCode">&lt;</code>
</div>
<a name="wp80117"> </a><div class="pCellBody">
<code class="cCode">&lt;=</code>
</div>
<a name="wp80118"> </a><div class="pCellBody">
<code class="cCode">&lt;&gt;</code> (not equal)
</div>
</td>
</tr>
  <tr align="left">    <td><a name="wp80120"> </a><div class="pCellBody">
Logical<br /><br />
</div>
</td>
    <td><a name="wp80122"> </a><div class="pCellBody">
<code class="cCode">NOT </code>
</div>
<a name="wp80123"> </a><div class="pCellBody">
<code class="cCode">AND </code>
</div>
<a name="wp80124"> </a><div class="pCellBody">
<code class="cCode">OR</code>
</div>
</td>
</tr>
</table>
</div>
<p class="pBody">
</p>
<a name="wp80127"> </a><h4 class="pHeading3">
BETWEEN Expressions
</h4>
<a name="wp80128"> </a><p class="pBody">
A <code class="cCode">BETWEEN</code> expression determines whether an arithmetic expression falls within a range of values. The syntax of the <code class="cCode">BETWEEN</code> expression follows:
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
between_expression ::= 
&nbsp;&nbsp;arithmetic_expression [<span style="font-weight: bold">NOT</span>] <span style="font-weight: bold">BETWEEN</span> 
&nbsp;&nbsp;arithmetic_expression <span style="font-weight: bold">AND</span> arithmetic_expression <a name="wp80129"> </a>
</pre></div>
<a name="wp80130"> </a><p class="pBody">
These two expressions are equivalent:
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
p.age BETWEEN 15 AND 19 
p.age &gt;= 15 AND p.age &lt;= 19<a name="wp80131"> </a>
</pre></div>
<a name="wp80132"> </a><p class="pBody">
The following two expressions are also equivalent:
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
p.age NOT BETWEEN 15 AND 19 
p.age &lt; 15 OR p.age &gt; 19<a name="wp80133"> </a>
</pre></div>
<a name="wp80134"> </a><p class="pBody">
If an arithmetic expression has a <code class="cCode">NULL</code> value, then the value of the <code class="cCode">BETWEEN</code> expression is unknown.
</p>
<a name="wp80135"> </a><h4 class="pHeading3">
IN Expressions
</h4>
<a name="wp80136"> </a><p class="pBody">
An <code class="cCode">IN</code> expression determines whether or not a string belongs to a set of string literals. Here is the syntax of the <code class="cCode">IN</code> expression:
</p>
<a name="wp81134"> </a><p class="pBody">
in_expression ::=<br />    cmp_path_expression [<code class="cCodeBold">NOT</code> ] <code class="cCodeBold">IN<br /></code>    ( {literal | input_parameter} <br />    [, { literal | input_parameter} ]*)
</p>
<a name="wp80138"> </a><p class="pBody">
The path expression must have a string or numeric value. If the path expression has a <code class="cCode">NULL</code> value, then the value of the <code class="cCode">IN</code> expression is unknown.
</p>
<a name="wp80139"> </a><p class="pBody">
In the following example, if the country is <code class="cCode">UK</code> the expression is <code class="cCode">TRUE</code>. If the country is <code class="cCode">Peru</code> it is <code class="cCode">FALSE</code>.
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
o.country IN (&#39;UK&#39;, &#39;US&#39;, &#39;France&#39;)<a name="wp80140"> </a>
</pre></div>
<a name="wp80141"> </a><h4 class="pHeading3">
LIKE Expressions
</h4>
<a name="wp80142"> </a><p class="pBody">
A <code class="cCode">LIKE</code> expression determines whether a wildcard pattern matches a string. Here is the syntax:
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
like_expression ::=
    cmp_path_expression [<code class="cCodeBold">NOT</code> ] <code class="cCodeBold">LIKE</code> 
    pattern_value [<code class="cCodeBold">ESCAPE</code> escape_character]<a name="wp80143"> </a>
</pre></div>
<a name="wp80144"> </a><p class="pBody">
The path expression must have a string or numeric value. If this value is <code class="cCode">NULL</code>, then the value of the <code class="cCode">LIKE</code> expression is unknown. The pattern value is a string literal that may contain wildcard characters. The underscore (_) wildcard character represents any single character. The percent (<code class="cCode">%</code>) wildcard character represents zero or more characters. The <code class="cCode">ESCAPE</code> clause specifies an escape character for the wildcard characters in the pattern value. <a  href="EJBQL5.html#wp80152">Table 24-3</a> shows some sample <code class="cCode">LIKE</code> expressions.
</p>
<a name="wp80189"> </a><p class="pBody">
</p><div align="left">
<table border="1" summary="LIKE Expression Examples" id="wp80152">
  <caption><a name="wp80152"> </a><div class="pTableTitle">
Table 24-3   LIKE Expression Examples
</div>
</caption>
  <tr align="center">    <th><a name="wp80158"> </a><div class="pCellHeading">
 Expression
</div>
</th>
    <th><a name="wp80160"> </a><div class="pCellHeading">
TRUE
</div>
</th>
    <th><a name="wp80162"> </a><div class="pCellHeading">
FALSE
</div>
</th>
</tr>
  <tr align="left">    <td><a name="wp80164"> </a><div class="pCellBody">
<code class="cCode">address.phone LIKE &#39;12%3&#39;</code>
</div>
</td>
    <td><a name="wp80166"> </a><div class="pCellBody">
<code class="cCode">&#39;123&#39;</code>
</div>
<a name="wp80167"> </a><div class="pCellBody">
<code class="cCode">&#39;12993&#39;</code>
</div>
</td>
    <td><a name="wp80169"> </a><div class="pCellBody">
<code class="cCode">&#39;1234&#39;</code>
</div>
</td>
</tr>
  <tr align="left">    <td><a name="wp80171"> </a><div class="pCellBody">
<code class="cCode">asentence.word LIKE &#39;l_se&#39;</code>
</div>
</td>
    <td><a name="wp80173"> </a><div class="pCellBody">
<code class="cCode">&#39;lose&#39;</code>
</div>
</td>
    <td><a name="wp80175"> </a><div class="pCellBody">
<code class="cCode">&#39;loose&#39;</code>
</div>
</td>
</tr>
  <tr align="left">    <td><a name="wp80177"> </a><div class="pCellBody">
<code class="cCode">aword.underscored LIKE &#39;\_%' ESCAPE &#39;\&#39;</code>
</div>
</td>
    <td><a name="wp80179"> </a><div class="pCellBody">
<code class="cCode">&#39;_foo&#39;</code>