Nullable

Nullable Data Types

NULL values are used to represent nonexistent or unknown values. Nullable data types allow storing NULL values. For example, the Nullable(Int64) type can store Int64 values as well as NULL.

Syntax

Define column field data types Nullable while creating a table is as follows:

CREATE TABLE test(
    id Int64,
    name String NULL,
    age Int32 NOT NULL
);

NULL indicates that the data type of this field is Nullable and can store NULL values. NOT NULL indicates that this field cannot store NULL values.

备注

Using Nullable will almost always have a negative impact on performance. If there is no explicit setting, Databend's column field data type defaults to NOT NULL.

Functions

Check whether the value is NULL or NOT NULL.

IS NULL

IS NOT NULL

Example

CREATE TABLE nullable_table(a Int8 NOT NULL, b Int8 NULL);

DESC nullable_table;
+-------+---------+------+---------+-------+
| Field | Type    | Null | Default | Extra |
+-------+---------+------+---------+-------+
| a     | TINYINT | NO   | 0       |       |
| b     | TINYINT | YES  | NULL    |       |
+-------+---------+------+---------+-------+

INSERT INTO nullable_table VALUES(1, NULL),(2, 3);

SELECT * FROM nullable_table;
+---+--------+
| a | b      |
+---+--------+
| 1 | <null> |
| 2 | 3      |
+---+--------+

SELECT b, b IS NULL, b IS NOT NULL FROM nullable_table;
+--------+-----------+---------------+
| b      | b IS NULL | b IS NOT NULL |
+--------+-----------+---------------+
| <null> | 1         | 0             |
| 3      | 0         | 1             |
+--------+-----------+---------------+