public String getExpression() {
        return this.expression;
    }
<p>
An expression that filters the partitions to be returned.
</p>
<p>
The expression uses SQL syntax similar to the SQL <code>WHERE</code> filter clause. The SQL statement parser <a
href="http://jsqlparser.sourceforge.net/home.php">JSQLParser</a> parses the expression.
</p>
<p>
<i>Operators</i>: The following are the operators that you can use in the <code>Expression</code> API call:
</p>
<dl>
<dt>=</dt>
<dd>
<p>
Checks whether the values of the two operands are equal; if yes, then the condition becomes true.
</p>
<p>
Example: Assume 'variable a' holds 10 and 'variable b' holds 20.
</p>
<p>
(a = b) is not true.
</p>
</dd>
<dt>&lt; &gt;</dt>
<dd>
<p>
Checks whether the values of two operands are equal; if the values are not equal, then the condition becomes
true.
</p>
<p>
Example: (a &lt; &gt; b) is true.
</p>
</dd>
<dt>&gt;</dt>
<dd>
<p>
Checks whether the value of the left operand is greater than the value of the right operand; if yes, then the
condition becomes true.
</p>
<p>
Example: (a &gt; b) is not true.
</p>
</dd>
<dt>&lt;</dt>
<dd>
<p>
Checks whether the value of the left operand is less than the value of the right operand; if yes, then the
condition becomes true.
</p>
<p>
Example: (a &lt; b) is true.
</p>
</dd>
<dt>&gt;=</dt>
<dd>
<p>
Checks whether the value of the left operand is greater than or equal to the value of the right operand; if yes,
then the condition becomes true.
</p>
<p>
Example: (a &gt;= b) is not true.
</p>
</dd>
<dt>&lt;=</dt>
<dd>
<p>
Checks whether the value of the left operand is less than or equal to the value of the right operand; if yes,
then the condition becomes true.
</p>
<p>
Example: (a &lt;= b) is true.
</p>
</dd>
<dt>AND, OR, IN, BETWEEN, LIKE, NOT, IS NULL</dt>
<dd>
<p>
Logical operators.
</p>
</dd>
</dl>
<p>
<i>Supported Partition Key Types</i>: The following are the supported partition keys.
</p>
<ul>
<li>
<p>
<code>string</code>
</p>
</li>
<li>
<p>
<code>date</code>
</p>
</li>
<li>
<p>
<code>timestamp</code>
</p>
</li>
<li>
<p>
<code>int</code>
</p>
</li>
<li>
<p>
<code>bigint</code>
</p>
</li>
<li>
<p>
<code>long</code>
</p>
</li>
<li>
<p>
<code>tinyint</code>
</p>
</li>
<li>
<p>
<code>smallint</code>
</p>
</li>
<li>
<p>
<code>decimal</code>
</p>
</li>
</ul>
<p>
If an type is encountered that is not valid, an exception is thrown.
</p>
<p>
The following list shows the valid operators on each type. When you define a crawler, the
<code>partitionKey</code> type is created as a <code>STRING</code>, to be compatible with the catalog partitions.
</p>
<p>
<i>Sample API Call</i>:
</p>

@return An expression that filters the partitions to be returned.</p>
        <p>
        The expression uses SQL syntax similar to the SQL <code>WHERE</code> filter clause. The SQL statement
        parser <a href="http://jsqlparser.sourceforge.net/home.php">JSQLParser</a> parses the expression.
        </p>
        <p>
        <i>Operators</i>: The following are the operators that you can use in the <code>Expression</code> API
        call:
        </p>
        <dl>
        <dt>=</dt>
        <dd>
        <p>
        Checks whether the values of the two operands are equal; if yes, then the condition becomes true.
        </p>
        <p>
        Example: Assume 'variable a' holds 10 and 'variable b' holds 20.
        </p>
        <p>
        (a = b) is not true.
        </p>
        </dd>
        <dt>&lt; &gt;</dt>
        <dd>
        <p>
        Checks whether the values of two operands are equal; if the values are not equal, then the condition
        becomes true.
        </p>
        <p>
        Example: (a &lt; &gt; b) is true.
        </p>
        </dd>
        <dt>&gt;</dt>
        <dd>
        <p>
        Checks whether the value of the left operand is greater than the value of the right operand; if yes, then
        the condition becomes true.
        </p>
        <p>
        Example: (a &gt; b) is not true.
        </p>
        </dd>
        <dt>&lt;</dt>
        <dd>
        <p>
        Checks whether the value of the left operand is less than the value of the right operand; if yes, then
        the condition becomes true.
        </p>
        <p>
        Example: (a &lt; b) is true.
        </p>
        </dd>
        <dt>&gt;=</dt>
        <dd>
        <p>
        Checks whether the value of the left operand is greater than or equal to the value of the right operand;
        if yes, then the condition becomes true.
        </p>
        <p>
        Example: (a &gt;= b) is not true.
        </p>
        </dd>
        <dt>&lt;=</dt>
        <dd>
        <p>
        Checks whether the value of the left operand is less than or equal to the value of the right operand; if
        yes, then the condition becomes true.
        </p>
        <p>
        Example: (a &lt;= b) is true.
        </p>
        </dd>
        <dt>AND, OR, IN, BETWEEN, LIKE, NOT, IS NULL</dt>
        <dd>
        <p>
        Logical operators.
        </p>
        </dd>
        </dl>
        <p>
        <i>Supported Partition Key Types</i>: The following are the supported partition keys.
        </p>
        <ul>
        <li>
        <p>
        <code>string</code>
        </p>
        </li>
        <li>
        <p>
        <code>date</code>
        </p>
        </li>
        <li>
        <p>
        <code>timestamp</code>
        </p>
        </li>
        <li>
        <p>
        <code>int</code>
        </p>
        </li>
        <li>
        <p>
        <code>bigint</code>
        </p>
        </li>
        <li>
        <p>
        <code>long</code>
        </p>
        </li>
        <li>
        <p>
        <code>tinyint</code>
        </p>
        </li>
        <li>
        <p>
        <code>smallint</code>
        </p>
        </li>
        <li>
        <p>
        <code>decimal</code>
        </p>
        </li>
        </ul>
        <p>
        If an type is encountered that is not valid, an exception is thrown.
        </p>
        <p>
        The following list shows the valid operators on each type. When you define a crawler, the
        <code>partitionKey</code> type is created as a <code>STRING</code>, to be compatible with the catalog
        partitions.
        </p>
        <p>
        <i>Sample API Call</i>:
aws-java-sdk-glue/src/main/java/com/amazonaws/services/glue/model/GetPartitionsRequest.java