SELECT statement has five major sections
1. SELECT key word
2. column specification
3. from key word
4. table or list of tables
5. where clause
Section 1, 2,3 and 4 are mandatory. 5 is optional.
Explanation with examples
Consider the table EMP with below structure
1) All records
Suppose user needs to see all records from EMP table. Below statement will pull all records from the table.
select * from EMP;
Note :- 1) In SQL `*` means all columns. Here table has four columns.
2) `;` is the terminator for the SQL statement.
3) SQL is not case sensitive.
2) Selected columns
select empno,salary from EMP;
The above statement fetches all empno and salary columns from EMP table
3) All records with where condition
select empno,salary from EMP where empno = 10;
The above statement will fetch a record with empno as value 10
4) All records using where condition and order by
select empno,salary from EMP where empno > 10 order by salary asc;
The above statement will fetch all record with empno as value > 10 in a ascending order of salary
Select SQL statement has lot of features, some of them are pretty straight forward and some of them are really complex. Normally SQL cannot be learnt by just reading. You just need to practice SQLs with real examples. For that we need a database installed in an operating system.
Each database will have a client utility to manage SQLs. In Oracle Database supplied with rwo SQL client utilities, SQL Plus and Oracle SQL Developer. SQL Plus is a command line utility and Oracle SQL Developer is a graphical user interface(GUI)
List of standalone tools available in the market.
1. TOAD – www.quest.com
2. Oracle SQL Developer – www.oracle.com
3. PL/SQL Developer – http://www.allroundautomations.com
4. Advanced Query Tool(AQT) – www.querytool.com