iTop的OQL（object query language）只支持一种类型，即查询语句，也就是SQL查询中的Select语句。OQL用于过滤或查询，可在iTop中用于邮件通知、审计规则等。OQL的返回值限于一个对象或者一组iTop对象。iTop将OQL最终翻译成对应的SQL Select语句，所以可以将OQL看做是SQL Select的一个子集，功能上不如SQL语句那么灵活，但足以应付iTop中各种操作。注意，OQL中的SQL保留字都必须大写，语法大小写敏感，所以每个对象的大小写必须准确。 OQL语法格式非常简单，形式如下，
SELECT [output_specification FROM] class_reference [class_joined] [WHERE expression] [UNION oql_query]
其中各项参数解释如下，
1. [output_specification FROM] ， 此为可选项，当使用了多个对象或者别名时才需要用到。 如：
SELECT p1 FROM Person as p1, 此处p1为Person的别名。
或者类似于：
SELECT p1,t1 FROM Person JOIN lnkPersonToTeam AS t1 ON t1.person_id=p1.id
2. class_reference, 查询的对象名，如上例中的Person。当不使用别名时，可以直接使用如下形式获取数据
>SELECT Person
则iTop自动从Person对象表中获取数据
如果iTop对象名或要使用的别名与SQL保留字冲突，则对象名或别名必须用``包装起来。如，
SELECT `Union`。
3. [class_joined]，如上面的例子，描述需要关联的其他对象。这个等于SQL语句的JOIN。具体格式为JOIN object2 ON object1.attribute1 [操作符] object2.attirbute1，其中操作符如下，
=, BELOW, BELOW STRICT, ABOVE or ABOVE STRICT.
其中BELOW和ABOVE相关的几个操作符用于当对象1和对象2有从属关系时。比如iTop中的服务和子服务。
4. [WHERE expression]，与SQL的WHERE语句一样的功能，expression支持的语法和函数下面再进行描述。
5. [UNION oql_query]， 与SQL的UNION的语句一样的功能。其中oql_query只要符合OQL语法即可。但此处的OQL返回的对象应该与主语句一致。
WHERE表达式语法， WHERE表达式可以由几个部分组成，即字符串、操作符、函数，最终形成一个布尔结果值，实现数据筛选。这个跟SQL的WHERE子句功能一致。
操作符表如下，
| Operator | Description |
|---|---|
| AND | Logical AND |
| OR | Logical OR |
| / | Division operator |
| = | Equality operator |
| >= | Greater than or equal operator |
| > | Greater than operator |
| <= | Less than or equal operator |
| < | Less than operator |
| - | Substraction operator |
| !=, <> | Non-equality operator |
| LIKE | Simple pattern matching |
| NOT LIKE | Negation of simple pattern matching |
| IN | List operator |
| NOT IN | Negation of list operator |
| & | New in 2.0.1 Bitwise operator “and”. This operator is different from the “logical” operator “AND” since it operates on every bit of each number. |
| New in 2.0.1 Bitwise operator “or”. This operator is different from the “logical” operator “OR” since it operates on every bit of each number. | |
| ^ | New in 2.0.1 Bitwise operator “xor”. |
| << | New in 2.0.1 Bitwise left shift |
| >> | New in 2.0.1 Bitwise right shift |
| REGEXP | Regular expression |
| MATCHES | New in 2.6.0 Fulltext match against a string. This operator only works with attributes of type TagSet. The supported syntax is attribute MATCHES 'code1 code2' |
函数列表如下，
| Function name | Description | Examples |
|---|---|---|
| COALESCE | Return the first non-NULL argument | COALESCE(field1, field2, 'Undefined') |
| CONCAT | Return concatenated string | CONCAT(firstname, ' ', lastname) |
| CURRENT_DATE | Return the current date | CURRENT_DATE() |
| DATE | Extract the date part of a date or datetime expression | DATE() |
| DATE_ADD | Add time values (intervals) to a date value. See allowed interval units below | DATE_ADD(NOW(), INTERVAL 1 HOUR) |
| DATE_FORMAT | Format date as specified | DATE_FORMAT('2009-10-04 22:23:00', '%W %M %Y') |
| DATE_SUB | Substract time values (intervals) from a date value. See allowed interval units below | DATE_SUB(NOW(), INTERVAL 5 MINUTE) |
| DAY | Return the day of the month (0-31) | DAY(DATE()) |
| ELT | Return string at index number | ELT(index, 'string1', 'string2', 'string3') |
| FLOOR | Return the largest integer value not greater than the argument | FLOOR(12.356) |
| FROM_DAYS | Convert a day number to a date | FROM_DAYS(12345) |
| IF | If/else construct | IF(a=b, 'equals', 'differs') |
| INET_ATON | Return the numeric value of an IP address | INET_ATON('15.15.121.12') |
| INET_NTOA | Return the IP address from a numeric value | INET_NTOA(1231654) |
| ISNULL | ISNULL(field1) | |
| MONTH | Return the month from the date passed | MONTH(DATE()) |
| NOW | Return the current date and time | NOW() |
| ROUND | Round the argument | ROUND(12.356, 2) |
| SUBSTR | Return the substring as specified | SUBSTR('abcdef', 2, 3) |
| TIME | Extract the time portion of the expression passed | TIME() |
| TO_DAYS | Return the date argument converted to days | TO_DAYS('2009-05-01') |
| TRIM | Remove leading and trailing spaces | TRIM(' blah ') |
| YEAR | Return the year from the date passed | YEAR(DATE()) |
其他说明， current_contact和current_user可以作为两个与当前登录用户相关的通用变量，从而可以在表达式中进行使用，使用格式如下，
:current_contact→attribute where 'attribute' is any code attribute of the Contact class :current_user→attribute where 'attribute' is any code attribute of the User class
如：
SELECT UserRequest WHERE agent_id = :current_contact->id AND status NOT IN ('closed', 'resolved')
