1，用逻辑运算符AND和 OR来联结多个查询条件
eg:
SQL> select * from customers where dob > to_date(‘1970-01-01’, ‘yyyy-mm-dd’) and first_name like ‘D_’;
CUSTOMER_ID FIRST_NAME LAST_NAME DOB PHONE
5 Doreen Blue 20-5月 -70
eg：
SQL> select * from customers where dob > to_date(‘1970-01-01’, ‘yyyy-mm-dd’) or first_name like ‘C%’;(每个条件的记录合在一起)
CUSTOMER_ID FIRST_NAME LAST_NAME DOB PHONE
2 Cynthia Green 05-2月 -68 800-555-1212
3 Steve White 16-3月 -71 800-555-1213
5 Doreen Blue 20-5月 -70 eg：
SQL> select * from customers where customer_id < 3;
CUSTOMER_ID FIRST_NAME LAST_NAME DOB PHONE
1 John Brown 01-1月 -65 800-555-1211
2 Cynthia Green 05-2月 -68 800-555-1212
SQL> select * from customers where not customer_id < 3;
CUSTOMER_ID FIRST_NAME LAST_NAME DOB PHONE
3 Steve White 16-3月 -71 800-555-1213
4 Gail Black 800-555-1214
5 Doreen Blue 20-5月 -70
SQL> select * from customers where not customer_id >= 3;
CUSTOMER_ID FIRST_NAME LAST_NAME DOB PHONE
1 John Brown 01-1月 -65 800-555-1211
2 Cynthia Green 05-2月 -68 800-555-1212
2，使用AND和 OR可以实现其他操作符的功能
[NOT] IN
[NOT] BETWEEN … AND …
3，使用NOT进行逻辑求反操作
4，运算符优先级
比较运算符 > NOT > AND > OR