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If you want to list tables in MySQL, you simply type the following command:

show tables

Oracle does not provide such a short cut. You have to type the following command:

select * from user_objects where object_type = 'TABLE'

The word TABLE must be uppercase. This would lisl all tables in the database. The same query could be modified slightly to list functions, procedures, sequences, view and more.

List functions

select * from user_objects where object_type = 'TABLE'

List views

Extract function is used to extract year, month, or date from a date or timezone hour or timezone minute from an interval. Examples:

To change the first letter of the word to cap, use the inicap function. Use upper to covert to uppercase and lower to convert to lower case. Examples:

NVL2 function extends the funcitonality of NVL function. NVL function prints the value of the variable unless a null value is encountered; in which case a value is substituted for the null. In addition to this, NVL2 also allows you to substitute a value if the value of the variable is not null. Syntax:

NVL2(variable, not_null_substitute, null_substitute)

Example

Suppose you have two dates and you want to compares the years rather the exact date. Make sure you know the format of the dates. The use the following code:

to_char(to_date(somedate, 'yyyymmdd'), 'YYYY') = to_char(to_date(somedate, 'yyyymmdd'), 'YYYY')

Change yyyymmdd to your date format.

The substr function extracts a substring from a string. Syntax:

substr( string, start position, length)

where the first position is 1 and the length of the substring is optional. Some examples

This error occurs if a wrong value is passed when converting a number or string to date. To fix this problem, find out what date format the date is stored in e.g. yyyymmdd, dd-mm-yy, dd-mon-yy, etc. Then rewrite the to_date() statement with the correct format. For example

Peculiarly, Oracle uses the double pipe ( || ) as a concatenation operator. Most programming languages use || for the or operator. Example:

insert into mytable (id, name) values (12, 'Mr. ' || lastname);

The field lastname is concatenated to the string Mr.

All columns of your SELECT must be listed in the GROUP BY expression. Alternately you can use functions MIN() or MAX() which compress results.

A package is an encapsulated collection of related PL/SQL types, objects, procedures, and other program objects. Packages have a package specification and a package body. Package specification declares constants, variables, types, cursors, exceptions and procedures. Package definition defines cursors and procedures.

Packages provide the advantages of modularity, information hiding, and encapsulation.

Package commands To create a package

CREATE PACKAGE package_name

To create package body