如果 MySQL EXPORT_SET() 函數(shù)中提供的任何參數(shù)為 NULL,則該函數(shù)將返回 NULL。以下示例將演示它 –
示例
mysql> Select EXPORT_SET(NULL, 'Y','N',',', 4); +----------------------------------+ | EXPORT_SET(NULL, 'Y','N',',', 4) | +----------------------------------+ | NULL | +----------------------------------+ 1 row in set (0.00 sec) mysql> Select EXPORT_SET(5, NULL,'N',',', 4); +--------------------------------+ | EXPORT_SET(5, NULL,'N',',', 4) | +--------------------------------+ | NULL | +--------------------------------+ 1 row in set (0.00 sec) mysql> Select EXPORT_SET(5, 'Y','N',',', NULL); +----------------------------------+ | EXPORT_SET(5, 'Y','N',',', NULL) | +----------------------------------+ | NULL | +----------------------------------+ 1 row in set (0.00 sec) mysql> Select EXPORT_SET(5, 'Y','N',NULL, 4); +--------------------------------+ | EXPORT_SET(5, 'Y','N',NULL, 4) | +--------------------------------+ | NULL | +--------------------------------+ 1 row in set (0.00 sec)
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