xulijia

and优先级比较高 or优先级低

select * from test where condition1 or condition2 and condition3;
其执行效果与下面的sql等价
select * from test where condition1 or (condition2 and condition3);

和这个的意思不一样哦
select * from test where （condition1 or condition2） and condition3;

create table test (col1 number,col2 number,col3 number);
insert into test values (1,2,3);
insert into test values (1,2,4);
insert into test values (1,3,5);
insert into test values (2,3,5);
insert into test values (7,3,5);

      COL1       COL2       COL3
---------- ---------- ----------
         1          2          4
         1          3          5
         2          3          5
         7          3          5
         2          2          3

select * from test where col1=2 or col2=3 and col3=5;
      COL1       COL2       COL3
---------- ---------- ----------
         1          3          5
         2          3          5
         7          3          5
         2          2          3

select * from test where col1=2 or (col2=3 and col3=5);
      COL1       COL2       COL3
---------- ---------- ----------
         1          3          5
         2          3          5
         7          3          5
         2          2          3

select * from test where （col1=2 or col2=3） and col3=5;
      COL1       COL2       COL3
---------- ---------- ----------
         1          3          5
         2          3          5
         7          3          5