Select

Basic SELECT statement:

SELECT COLUMNS FROM TABLE_NAME;

COLUMNS may be:

·         *: all of fields of the table

·         A field name of the table

·         Many fields are separated by a comma ‘,’

Examples Statement:

SELECT 1 FROM DUAL;

Result:

Examples Statement:

SELECT 1 AS “DEMO” FROM DUAL;

Result:

Note: Dual is a special table existing in memory, means that data on this table will be lost after finish sessions.
Examples Statement:

SELECT TABLE_NAME FROM USER_TABLES

Note: USER_TABLES is the table storing information of user’s tables.
Examples Statement:

SELECT * FROM REGIONS;

The REGIONS table has 4 records and this statement returns all 4 records.
Examples Statement:

SELECT REGION_ID AS “ID”, REGION_NAME AS “NAME” FROM REGIONS;

This statement selects two columns: REGION_ID and REGION_NAME. We also could use alias to change the display names for columns.