nullif 語(yǔ)句

簡(jiǎn)單寫法:

SELECT NULLIF(value1,value2); 當(dāng)value1與value2的結(jié)果相同時(shí),輸出結(jié)果為null; 否則為value1的結(jié)果;

測(cè)試1:

SELECT NULLIF(111,111); SELECT NULLIF('111',111); SELECT NULLIF(111,'111'); SELECT NULLIF('111','111'); 以上四個(gè)結(jié)果都為null;

測(cè)試2:

SELECT NULLIF(111,222); SELECT NULLIF('111',222); SELECT NULLIF(111,'222'); SELECT NULLIF('111','222'); 以上四個(gè)結(jié)果都為value1的值:111