NULL Handling

NULL is the term used to represent a missing value. A NULL value in a table is a value in a field that appears to be blank. A field with a NULL value is a field with no value.

This page summarizes how NULL values are handled in CockroachDB SQL. Each topic is demonstrated via the .

When using the built-in client, NULL values are displayed using the word NULL. This distinguishes them from a character field that contains an empty string ("").

NULLs and simple comparisons

Any simple comparison between a value and NULL results in NULL. The remaining cases are described in the next section.

This behavior is consistent with PostgreSQL as well as all other major RDBMS’s.

> INSERT INTO customers (customer_id, cust_name, cust_email) VALUES (1, 'Smith', NULL);

> CREATE TABLE t1(
  a INT,
  b INT,
  c INT
);

> INSERT INTO t1 VALUES(1, 0, 0);

> INSERT INTO t1 VALUES(2, 0, 1);

> INSERT INTO t1 VALUES(3, 1, 0);

> INSERT INTO t1 VALUES(4, 1, 1);

> INSERT INTO t1 VALUES(5, NULL, 0);

> INSERT INTO t1 VALUES(6, NULL, 1);

> INSERT INTO t1 VALUES(7, NULL, NULL);

> SELECT * FROM t1;

+---+------+------+
| a |  b   |  c   |
+---+------+------+
| 1 |    0 |    0 |
| 2 |    0 |    1 |
| 3 |    1 |    0 |
| 4 |    1 |    1 |
| 5 | NULL |    0 |
| 6 | NULL |    1 |
| 7 | NULL | NULL |
+---+------+------+

> SELECT * FROM t1 WHERE b < 10;

+---+---+---+
| a | b | c |
+---+---+---+
| 1 | 0 | 0 |
| 2 | 0 | 1 |
| 3 | 1 | 0 |
| 4 | 1 | 1 |
+---+---+---+

> SELECT * FROM t1 WHERE NOT b > 10;

+---+---+---+
| a | b | c |
+---+---+---+
| 1 | 0 | 0 |
| 2 | 0 | 1 |
| 3 | 1 | 0 |
| 4 | 1 | 1 |
+---+---+---+

> SELECT * FROM t1 WHERE b < 10 OR c = 1;

+---+------+---+
| a |  b   | c |
+---+------+---+
| 1 |    0 | 0 |
| 2 |    0 | 1 |
| 3 |    1 | 0 |
| 4 |    1 | 1 |
| 6 | NULL | 1 |
+---+------+---+

> SELECT * FROM t1 WHERE b < 10 AND c = 1;

+---+---+---+
| a | b | c |
+---+---+---+
| 2 | 0 | 1 |
| 4 | 1 | 1 |
+---+---+---+

> SELECT * FROM t1 WHERE NOT (b < 10 AND c = 1);

+---+------+---+
| a |  b   | c |
+---+------+---+
| 1 |    0 | 0 |
| 3 |    1 | 0 |
| 5 | NULL | 0 |
+---+------+---+

> SELECT * FROM t1 WHERE NOT (c = 1 AND b < 10);

+---+------+---+
| a |  b   | c |
+---+------+---+
| 1 |    0 | 0 |
| 3 |    1 | 0 |
| 5 | NULL | 0 |
+---+------+---+

Use the IS NULL or IS NOT NULL clauses when checking for NULL values.

> SELECT * FROM t1 WHERE b IS NULL AND c IS NOT NULL;

+---+------+---+
| a |  b   | c |
+---+------+---+
| 5 | NULL | 0 |
| 6 | NULL | 1 |
+---+------+---+

NULLs and conditional operators

The (including IF, COALESCE, IFNULL) only evaluate some operands depending on the value of a condition operand, so their result is not always NULL depending on the given operands.

For example, COALESCE(1, NULL) will always return 1 even though the second operand is NULL.

NULLs and ternary logic

AND, OR and IS implement ternary logic, as follows.

Expression	Result
FALSE AND FALSE	FALSE
FALSE AND TRUE	FALSE
FALSE AND NULL	FALSE
TRUE AND FALSE	FALSE
TRUE AND TRUE	TRUE
TRUE AND NULL	NULL
NULL AND FALSE	FALSE
NULL AND TRUE	NULL
NULL AND NULL	NULL

Expression	Result
FALSE OR FALSE	FALSE
FALSE OR TRUE	TRUE
FALSE OR NULL	NULL
TRUE OR FALSE	TRUE
TRUE OR TRUE	TRUE
TRUE OR NULL	TRUE
NULL OR FALSE	NULL
NULL OR TRUE	TRUE
NULL OR NULL	NULL

Expression	Result
FALSE IS FALSE	TRUE
FALSE IS TRUE	FALSE
FALSE IS NULL	FALSE
TRUE IS FALSE	FALSE
TRUE IS TRUE	TRUE
TRUE IS NULL	FALSE
NULL IS FALSE	FALSE
NULL IS TRUE	FALSE
NULL IS NULL	TRUE

NULLs and arithmetic

Arithmetic operations involving a NULL value will yield a NULL result.

> SELECT a, b, c, b*0, b*c, b+c FROM t1;

+---+------+------+-------+-------+-------+
| a |  b   |  c   | b * 0 | b * c | b + c |
+---+------+------+-------+-------+-------+
| 1 |    0 |    0 |     0 |     0 |     0 |
| 2 |    0 |    1 |     0 |     0 |     1 |
| 3 |    1 |    0 |     0 |     0 |     1 |
| 4 |    1 |    1 |     0 |     1 |     2 |
| 5 | NULL |    0 | NULL  | NULL  | NULL  |
| 6 | NULL |    1 | NULL  | NULL  | NULL  |
| 7 | NULL | NULL | NULL  | NULL  | NULL  |
+---+------+------+-------+-------+-------+

NULLs and aggregate functions

Aggregate are those that operate on a set of rows and return a single value. The example data has been repeated here to make it easier to understand the results.

> SELECT * FROM t1;

+---+------+------+
| a |  b   |  c   |
+---+------+------+
| 1 |    0 |    0 |
| 2 |    0 |    1 |
| 3 |    1 |    0 |
| 4 |    1 |    1 |
| 5 | NULL |    0 |
| 6 | NULL |    1 |
| 7 | NULL | NULL |
+---+------+------+

> SELECT COUNT(*), COUNT(b), SUM(b), AVG(b), MIN(b), MAX(b) FROM t1;

+----------+----------+--------+--------------------+--------+--------+
| COUNT(*) | COUNT(b) | SUM(b) |       AVG(b)       | MIN(b) | MAX(b) |
+----------+----------+--------+--------------------+--------+--------+
|        7 |        4 |      2 | 0.5000000000000000 |      0 |      1 |
+----------+----------+--------+--------------------+--------+--------+

Note the following:

• NULL values are not included in the COUNT() of a column. COUNT(*) returns 7 while COUNT(b) returns 4.

• NULL values are not considered as high or low values in MIN() or MAX().

• AVG(b) returns SUM(b)/COUNT(b), which is different than AVG(*) as NULL values are not considered in the COUNT(b) of rows. See NULLs as Other Values for more details.

NULL as a distinct value

NULL values are considered distinct from other values and are included in the list of distinct values from a column.

> SELECT DISTINCT b FROM t1;

+------+
|  b   |
+------+
|    0 |
|    1 |
| NULL |
+------+

However, counting the number of distinct values excludes NULLs, which is consistent with the COUNT() function.

> SELECT COUNT(DISTINCT b) FROM t1;

+-------------------+
| count(DISTINCT b) |
+-------------------+
|                 2 |
+-------------------+

NULLs as other values

In some cases, you may want to include NULL values in arithmetic or aggregate function calculations. To do so, use the IFNULL() function to substitute a value for NULL during calculations.

For example, let’s say you want to calculate the average value of column b as being the SUM() of all numbers in b divided by the total number of rows, regardless of whether b’s value is NULL. In this case, you would use AVG(IFNULL(b, 0)), where IFNULL(b, 0) substitutes a value of zero (0) for NULLs during the calculation.

> SELECT COUNT(*), COUNT(b), SUM(b), AVG(b), AVG(IFNULL(b, 0)), MIN(b), MAX(b) FROM t1;

+----------+----------+--------+--------------------+--------------------+--------+--------+
| COUNT(*) | COUNT(b) | SUM(b) |       AVG(b)       | AVG(IFNULL(b, 0))  | MIN(b) | MAX(b) |
+----------+----------+--------+--------------------+--------------------+--------+--------+
|        7 |        4 |      2 | 0.5000000000000000 | 0.2857142857142857 |      0 |      1 |
+----------+----------+--------+--------------------+--------------------+--------+--------+

NULLs and set operations

NULL values are considered as part of a UNION .

> SELECT b FROM t1 UNION SELECT b FROM t1;

+------+
|  b   |
+------+
|    0 |
|    1 |
| NULL |
+------+

NULLs and sorting

When containing NULL values, CockroachDB sorts NULL values first with ASC and last with DESC. This differs from PostgreSQL, which sorts NULL values last with ASC and first with DESC.

Use the NULLS FIRST and NULLS LAST options of the to change where NULL values appear in the sort order.

> SELECT * FROM t1 ORDER BY b ASC;

+---+------+------+
| a |  b   |  c   |
+---+------+------+
| 6 | NULL |    1 |
| 5 | NULL |    0 |
| 7 | NULL | NULL |
| 1 |    0 |    0 |
| 2 |    0 |    1 |
| 4 |    1 |    1 |
| 3 |    1 |    0 |
+---+------+------+

> SELECT * FROM t1 ORDER BY b DESC;

+---+------+------+
| a |  b   |  c   |
+---+------+------+
| 4 |    1 |    1 |
| 3 |    1 |    0 |
| 2 |    0 |    1 |
| 1 |    0 |    0 |
| 7 | NULL | NULL |
| 6 | NULL |    1 |
| 5 | NULL |    0 |
+---+------+------+

NULLs and unique constraints

NULL values are not considered unique. Therefore, if a table has a UNIQUE constraint on one or more columns that are optional (nullable), it is possible to insert multiple rows with NULL values in those columns, as shown in the example below.

> CREATE TABLE t2(a INT, b INT UNIQUE);

> INSERT INTO t2 VALUES(1, 1);

> INSERT INTO t2 VALUES(2, NULL);

> INSERT INTO t2 VALUES(3, NULL);

> SELECT * FROM t2;

+---+------+
| a |  b   |
+---+------+
| 1 |    1 |
| 2 | NULL |
| 3 | NULL |
+---+------+

NULLs and CHECK Constraints

A expression that evaluates to NULL is considered to pass, allowing for concise expressions like discount < price without worrying about adding OR discount IS NULL clauses. When non-null validation is desired, the usual NOT NULL constraint can be used alongside a CHECK constraint.

> CREATE TABLE products (id STRING PRIMARY KEY, price INT NOT NULL CHECK (price > 0), discount INT, CHECK (discount <= price));

> INSERT INTO products (id, price) VALUES ('ncc-1701-d', 100);

> INSERT INTO products (id, price, discount) VALUES ('ncc-1701-a', 100, 50);

> SELECT * FROM products;

+----------+-------+----------+
|    id    | price | discount |
+----------+-------+----------+
| ncc1701a |   100 |       50 |
| ncc1701d |   100 | NULL     |
+----------+-------+----------+

> INSERT INTO products (id, price) VALUES ('ncc-1701-b', -5);

failed to satisfy CHECK constraint (price > 0)

> INSERT INTO products (id, price, discount) VALUES ('ncc-1701-b', 100, 150);

failed to satisfy CHECK constraint (discount <= price)

NULLs and concatenation with other types

Concatenation between a non-NULL value and a NULL value results in a NULL value.

In CockroachDB v20.2 and earlier, for all values other than , concatenation between a non-NULL value and a NULL value results in an of the non-NULL value’s type. To return an ARRAY of a specific type from a NULL concatenation in CockroachDB v21.1 and later, the NULL value to an ARRAY.

For example:

> SELECT NULL || 1;

  ?column?
------------
  NULL
(1 row)

> SELECT NULL || `item`;

  ?column?
------------
  NULL
(1 row)

Known limitations

• By default, CockroachDB orders NULLs before all other values. For compatibility with PostgreSQL, the null_ordered_last was added, which changes the default to order NULL values after all other values. This works in most cases, due to some transformations CockroachDB makes in the optimizer to add extra ordering columns. However, it does not work when the ordering column is a tuple.