EnterpriseDB: CHAR Data Type Oracle Tips by Burleson Consulting

CHAR

EnterpriseDB also supports a CHAR data type.  CHAR is a fixed length data type. If you don't specify a size, it defaults to 1.

A fixed length data type always uses all of its declared length.  If you declare a CHAR(50) and assign it a value, it will be padded to 50 characters with spaces.  A VARCHAR2(50) does not pad.  I don't use CHAR very often.  VARCHAR2 is much more useful to me as it only requires storage for characters that are actually used.

To declare a 50-character CHAR variable, you would simply enter the variable name followed by CHAR(50). This variable or column would pad to 50 spaces when you add any data, regardless of the data's size.

For example, if I declare a variable:

v_data CHAR(50);

My variable name is v_data, the data type is CHAR and the declared length is 50.  The actual length stored is 0 characters because the variable is null.  If we assign it a value:

v_data := 'LEWIS';

We gave the variable v_data that value of LEWIS.  LEWIS is 5 characters but our variable now holds 50 characters:  5 characters for LEWIS and 45 spaces.  If v_data had been a VARCHAR2(50), its length would only be 5.

The only benefit of a CHAR to a VARCHAR2 is that you always know exactly how long a CHAR column is going to be.  Either it will be NULL or it will be its declared length.  A VARCHAR2 will always either be NULL or it will be some length less than or equal to its max length.

Synonyms for CHAR are:

* CHARACTER

CLOB

In Oracle, a CLOB data type is used to store very large text documents.  In Oracle 10g, on a 64-bit machine, a CLOB can store 128 terabytes of data.  EnterpriseDB does not support the CLOB data type directly.  A CLOB declaration is transformed to the TEXT data type.  A TEXT field can be up to a gigabyte in size.  TEXT works like a VARCHAR2 but without the declared max size.

Synonyms for CLOB are:

* LONG

* LONG VARCHAR

* LONGTEXT

* LVARCHAR

* MEDIUMTEXT

* TEXT

If I were to create a table with the text data types that we have discussed, the syntax would look like this:

CREATE TABLE text_table (
  name VARCHAR2(50),
  address CHAR(50),
  comments CLOB
);

Now that we have a table, we can insert into it:

INSERT INTO text_table (name, address, comments)
  VALUES ('Lewis', 'New Orleans', 'My Name is Lewis and My address is New Orleans.');

If we selected the data back out from the table:

SELECT name, address, comments
  FROM text_table;

I can use EnterpriseDB PSQL (which I spoke about in Chapter 2) to run these commands.

edb=# CREATE TABLE text_table (
edb(#   name VARCHAR2(50),
edb(#   address CHAR(50),
edb(#   comments CLOB
edb(# );
CREATE TABLE
edb=# INSERT INTO text_table (name, address, comments)
edb-#   VALUES ('Lewis', 'New Orleans', 'My Name is Lewis and My address is New
Orleans.');
INSERT 0 1
edb=# commit;
COMMIT
edb=# SELECT name, address, comments
edb-#   FROM text_table;

 name  |             address              |                    comments  

-------+----------------------------------+--------------------------------------------- Lewis | New Orleans                      | My Name is Lewis and My address is New Orleans.
(1 row)

edb=#

I will use PSQL to run commands for the remainder of this chapter.

This is an excerpt from the book "EnterpriseDB: The Definitive Reference" by Rampant TechPress.