tip: 短路运算减少执行语句,优化了性能! 运算符里：AND和OR都有短路计算功能,常见函数里又是怎么样的呢？ 一：非短路函数 1：NVL 2: NVL2 二：短路函数 1: decode 2: case when 3: coalesce 三：实验
SQL> select * from v$version; BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production PL/SQL Release 11.2.0.1.0 - Production CORE 11.2.0.1.0 Production TNS for 64-bit Windows: Version 11.2.0.1.0 - Production NLSRTL Version 11.2.0.1.0 - Production --NVL(1,0,1) = 2 被短路 SQL> select * from dual where 1 = 1 or nvl(1/0,2) = 2; DU -- X --NVL(1,0,1) = 2 被短路 SQL> select * from dual where 1 = 2 and nvl(1/0,1) = 2; no rows selected --1/0 继续运算,非短路 SQL> select nvl(1,1/0) from dual; select nvl(1,1/0) from dual * ERROR at line 1: ORA-01476: divisor is equal to zero --1/0 继续运算,非短路 SQL> select nvl2(null,1/0,2) from dual; select nvl2(null,1/0,2) from dual * ERROR at line 1: ORA-01476: divisor is equal to zero --1/0 没有运算,短路 SQL> select decode(1,1,2,1/0) from dual; DECODE(1,1,2,1/0) ----------------- 2 --1/0 没有运算,短路 SQL> select coalesce(null,1,1/0) from dual; COALESCE(NULL,1,1/0) -------------------- 1 --1/0 没有运算,短路 SQL> select case when 1 is not null then 1 else 1/0 end col from dual; COL ---------- 1
