coalesce 函数 :Oracle COALESCE函数语法为COALESCE(表达式1,表达式2,...,表达式n)，n>=2,此表达式的功能为返回第一个不为空的表达式，如果都为空则返回空值。注意：所有表达式必须为同一类型或者能转换成同一类型。返回第一个不为空的CREATE OR REPLACE VIEW v ASSELECT NULL AS C1, NULL AS C2,    1 AS C3, NULL AS C4,    2 AS C5, NULL AS C6 FROM DUAL UNION ALLSELECT NULL AS C1, NULL AS C2, NULL AS C3,    3 AS C4, NULL AS C5,    2 AS C6 FROM DUAL;SQL> select * from v;C C	    C3	       C4	  C5	     C6- - ---------- ---------- ---------- ----------	     1			   2			3		      2SQL> SELECT COALESCE(C1, C2, C3, C4, C5, C6) AS c FROM V;	 C----------	 1	 3如果用nvl函数呢？SELECT nvl(nvl(nvl(nvl(nvl(c1, c2), c3), c4), c5), c6) AS c FROM v;