SQL FOREIGN KEY Constraint A FOREIGN KEY in one table points to a PRIMARY KEY in another table. CREATE TABLE Orders ( O_Id int NOT NULL PRIMARY KEY, OrderNo int NOT NULL, P_Id int FOREIGN KEY REFERENCES Persons(P_Id) ) To DROP a FOREIGN KEY Constraint...

SQL Constraints SQL constraints are used to specify rules for the data in a table. If there is any violation between the constraint and the data action, the action is aborted by the constraint. Constraints can be specified when the table is created (inside...

SQL CHECK Constraint The CHECK constraint is used to limit the value range that can be placed in a column. If you define a CHECK constraint on a single column it allows only certain values for this column. If you define a CHECK constraint on a table it...

SQL Scalar functions SQL scalar functions return a single value, based on the input value. Useful scalar functions: UCASE() - Converts a field to upper case LCASE() - Converts a field to lower case MID() - Extract characters from a text field LEN() -...

SQL Aggregate Functions SQL aggregate functions return a single value, calculated from values in a column. Useful aggregate functions: AVG() - Returns the average value COUNT() - Returns the number of rows FIRST() - Returns the first value LAST() - Returns...

VIEW This is an important concept in SQL. A View is nothing but a window of an existing table. In other words it is a logical representation that is created from one or existing base table. After creation of view it can be used just as a base table. That...

RDBMS RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL, and for all modern database systems such as MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access. The data in RDBMS is stored in database objects called tables....

Oracle 11g offers a new twist on triggers, the compound trigger, a trigger than can act both before and after an update, insert or delete has occurred. This makes possible the abilty in one trigger to perform processing similar to a stored procedure without...

Complex Queries in SQL ----------------------------------------- Hai All, These questions are the most frequently asked in interviews. 1) To fetch ALTERNATE records from a table. (EVEN NUMBERED) select * from emp where rowid in (select decode(mod(rownum,2),0,rowid,...

PL/SQL Implicit Cursor Oracle uses implicit cursors for its internal processing. Even if we execute a SELECT statement or DML statement Oracle reserves a private SQL area in memory called cursor. Implicit cursor scope you can get information from cursor...