Tests a value against a boolean value, where boolean_value
can be TRUE, FALSE, or UNKNOWN.
There is an important difference between using IS TRUE or comparing a value with TRUE using =
. When using =
, only 1
equals to TRUE. But when using IS TRUE, all values which are logically true (like a number > 1) return TRUE.
SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;
+-----------+------------+-----------------+
| 1 IS TRUE | 0 IS FALSE | NULL IS UNKNOWN |
+-----------+------------+-----------------+
| 1 | 1 | 1 |
+-----------+------------+-----------------+
Difference between =
and IS TRUE
:
SELECT 2 = TRUE, 2 IS TRUE;
+----------+-----------+
| 2 = TRUE | 2 IS TRUE |
+----------+-----------+
| 0 | 1 |
+----------+-----------+
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