Categories:: Conditional expression functions

COALESCE¶

Returns the first non-NULL expression among its arguments, or NULL if all its arguments are NULL.

Syntax¶

COALESCE( <expr1> , <expr2> [ , ... , <exprN> ] )

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Usage notes¶

If possible, pass in arguments of the same type. Avoid passing in arguments of different types.
If one of the arguments is a number, the function coerces non-numeric string arguments (e.g. 'a string') and string arguments that are not constants to the type NUMBER(18,5).

For numeric string arguments that are not constants, if NUMBER(18,5) is not sufficient to represent the numeric value, you should cast the argument to a type that can represent the value.

Collation details¶

The collation specifications of all input arguments must be compatible.
The comparisons follow the collation based on the input arguments’ collations and precedences.
The collation of the result of the function is the highest-precedence collation of the inputs.

Examples¶

SELECT column1, column2, column3, coalesce(column1, column2, column3)
FROM (values
  (1,    2,    3   ),
  (null, 2,    3   ),
  (null, null, 3   ),
  (null, null, null),
  (1,    null, 3   ),
  (1,    null, null),
  (1,    2,    null)
) v;

+---------+---------+---------+-------------------------------------+
| COLUMN1 | COLUMN2 | COLUMN3 | COALESCE(COLUMN1, COLUMN2, COLUMN3) |
|---------+---------+---------+-------------------------------------|
|       1 |       2 |       3 |                                   1 |
|    NULL |       2 |       3 |                                   2 |
|    NULL |    NULL |       3 |                                   3 |
|    NULL |    NULL |    NULL |                                NULL |
|       1 |    NULL |       3 |                                   1 |
|       1 |    NULL |    NULL |                                   1 |
|       1 |       2 |    NULL |                                   1 |
+---------+---------+---------+-------------------------------------+

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