函数说明
根据一个布尔值来检验一个值,
此处的布尔值可以是TRUE、
FALSE 或UNKNOWN。
示例
示例1:使用IS 语句检验1、0 和NULL。
gbase> SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN FROM t;
+-----------+------------+------------------+
| 1 IS TRUE | 0 IS FALSE | NULL IS UNKNOWN |
+-----------+------------+------------------+
| 1 | 1 | 1 |
+-----------+------------+------------------+
1 row in set
示例2:使用IS NOT 语句检验1、0 和NULL。
gbase> SELECT 1 IS NOT UNKNOWN, 0 IS NOT UNKNOWN, NULL IS NOT UNKNOWN FROM t;
+------------------+------------------+----------------------+
| 1 IS NOT UNKNOWN | 0 IS NOT UNKNOWN | NULL IS NOT UNKNOWN |
+------------------+------------------+----------------------+
| 1 | 1 | 0 |
+------------------+------------------+----------------------+
1 row in set
示例3:使用IS 语句检验一个值是否是NULL。
gbase> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL FROM t;
+-----------+-----------+---------------+
| 1 IS NULL | 0 IS NULL | NULL IS NULL |
+-----------+-----------+---------------+
| 0 | 0 | 1 |
+-----------+-----------+---------------+
1 row in set
示例4:使用IS NOT 语句检验一个值是否是NULL。
gbase> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL FROM t;
+---------------+---------------+-------------------+
| 1 IS NOT NULL | 0 IS NOT NULL | NULL IS NOT NULL |
+---------------+---------------+-------------------+
| 1 | 1 | 0 |
+---------------+---------------+-------------------+
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1 row in set