Conditions are used to determine data values and return
UNKNOWN. A condition is a combination of one or more components, such as expressions and logical (Boolean) operators. You must use valid syntax for conditions in SQL statements.
NLS_SORT parameters jointly affect the sorting and comparison of characters. If the
NLS_COMP parameter in the database is set to
LINGUISTIC, all the entities that are described in this Developer Guide follow the rules that are specified by the
NLS_SORT parameter. If the
NLS_COMP parameter is not set to
LINGUISTIC, the functions are not affected by
NLS_SORT. You can directly specify the value of
NLS_SORT. If you do not specify it, it inherits the value of
You can use conditions in the
WHERE clauses of these statements:
You can use conditions in these clauses of the
A condition can be called a logical data type, although ApsaraDB for OceanBase does not officially support such a data type.
For example, the simple condition 1 = 1 returns the result of TRUE.
The following more complex condition adds the value of salary to the value of commission_pct and checks whether the sum is greater than 25,000. The
NVL function replaces NULL values in salary with 0.
NVL(salary, 0) + NVL(salary + (salary * commission_pct, 0) > 25000)
AND condition can combine multiple conditions into a single condition.
(1 = 1) AND (5 < 7)
The following conditions are valid in SQL statements:
name = 'SMITH' employees.department_id = departments.department_id hire_date > '01-JAN-08' job_id IN ('SA_MAN', 'SA_REP') salary BETWEEN 5000 AND 10000 commission_pct IS NULL AND salary = 2100
Condition precedence indicates the order in which ApsaraDB for OceanBase checks different conditions in the same expression. When an expression that contains multiple conditions is computed, the conditions that have higher precedence are checked first, and then the conditions that have lower precedence. The conditions that have equal precedence are checked from left to right. For example, multiple conditions that are connected by
OR cannot be checked from left to right. The
AND condition is computed first, and then the
List of SQL condition precedence
=, ! =, <, >, <=, >=
IS [NOT] NULL, LIKE, [NOT] BETWEEN, [NOT] IN, EXISTS, and IS OF
Exponentiation and logical negation
The levels of precedence are listed from high to low. Conditions that are listed on the same line have the same precedence.