SQL语句PART1

Oracle SQL(partI)
Data manipulation language(DML): select, insert, update, delete, merge.
Data definition language(DDL): create, alter, drop, rename, truncate, comment
Data control language(DCL): grant, revoke
Transaction control: commit, rollback, savepoint
Arithmetic Expressions:
+, -, *, /
1) Arithmetic expressions containing a null value evaluate to null 
Column Alias
1) requires double quotation marks if it contains spaces or special characters, or if it is case-sensitive
e.g.: select last_name as name, commission_pct comm from employees;
e.g.: select last_name  "Name", salary*12 "Annual Salary" from employees 
Alternative Quote(q) Operator
e.g.: select depart_name||' Department'||q'['s Manager is ]'||manager_id as "Department and Manager"
results:
Department and Manager
Administrator Department's Manager is Me
...
Using DESCRIBE to display the table structure
e.g.: describe tb1;
Rules of precedence for operators in an expression
1   Arithmetic operators
2  Concatenation operator
3  Comparison conditions
4  IS [NOT] NULL, LIKE, [NOT] IN
5  [NOT] BETWEEN
6  Not equal to
7  NOT logical condition
8  AND logical condition
9  OR logical condition
e.g.: select last_name, job_id, salary from employees where job_id='SA_REP' or job_id='AD_PRES' and salary>15000;
means: select job_id='SA_REP' or (job_id='AD_PRES' and salary>15000)
e.g.: select last_name, job_id, salary from employees where (job_id='SA_REP' or job_id='AD_PRES') and salary>15000
Sorting:
can be sorted by column's numeric position
eg.: select last_name, job_id, department_id, hire_date from employees order by 3; 
Substitution Variables
1. temporarily store values with & and &&
2. using in following conditions: where conditions, order by clauses, column expressions, table names, entire select statements.
e.g.: select employee_id, last_name, salary, department_id from employees where e