《oracle pl/sql programming》 第7章 working with data

1.命名
在使用變量或常量之前，需要先對它進行聲明，聲明應遵循以下規則：
· 名稱的寬度在30個字符以內
· 名稱以字母開頭，后續只可以是字母、數字以及$,#,_
· 名稱忽略大小寫（雙引號命名法除外）

2.數據類型
Character：char,varchar2,...
Number
Date,Timestamp,interval
Boolean
Binary（二進制）:BLOB,BFILE
ROWID
REF cursor
Internet DataType
"Any" DataType
User-Defined DataType

3.聲明數據
聲明變量
name datatype [NOT NULL] [default_assignment];
example:
DECLARE
-- Simple declaration of numeric variable
l_total_count NUMBER;

-- Declaration of number that rounds to nearest hundredth (cent):
l_dollar_amount NUMBER (10,2);

-- A single date value, assigned a default value of "right now"
-- and it can never be NULL
l_right_now DATE NOT NULL DEFAULT SYSDATE;

-- Using the assignment operator for the default value specification
l_favorite_flavor VARCHAR2(100) := 'Anything with chocolate, actually';

-- Two-step declaration process for associative array.
-- First, the type of table:
TYPE list_of_books_t IS TABLE OF book%ROWTYPE INDEX BY BINARY_INTEGER;

-- And now the specific list to be manipulated in this block:
oreilly_oracle_books list_of_books_t;

聲明常量
name CONSTANT datatype [NOT NULL] := | DEFAULT default_value;
example:
DECLARE
-- The current year number; it's not going to change during my session.
l_curr_year CONSTANT PLS_INTEGER :=
TO_NUMBER (TO_CHAR (SYSDATE, 'YYYY'));

-- Using the DEFAULT keyword
l_author CONSTANT VARCHAR2(100) DEFAULT 'Bill Pribyl';

-- Declare a complex datatype as a constant
-- this isn't just for scalars!
l_steven CONSTANT person_ot :=
person_ot ('HUMAN', 'Steven Feuerstein', 175, '09-23-1958');

指示器聲明
兩種形式：
variable name type attribute%TYPE [optional default value assignment];
variable name table_name | cursor_name%ROWTYPE [optional default value
assignment];
example:
l_company_id company.company_id%TYPE;

DECLARE
l_book book%ROWTYPE;
BEGIN
SELECT * INTO l_book
FROM book
WHERE isbn = '1-56592-335-9'
process_book (l_book);
END;

DECLARE
CURSOR book_cur IS
SELECT author, title FROM book
WHERE isbn = '1-56592-335-9'

l_book book_cur%ROWTYPE;
BEGIN
OPEN book_cur;
FETCH book_cur INTO l_book;
process_book (l_book);
END;

不能使用類型指示器的情況(NOT NULL)
DECLARE
max_available_date DATE NOT NULL :=
L*_DAY (ADD_MONTHS (SYSDATE, 3));
last_ship_date max_available_date%TYPE;
以上代碼將產生編譯錯誤：
PLS_00218: a variable declared NOT NULL must have an initialization assignment.

4.自定義子數據類型
兩種形式：限制型/非限制型
限制型舉例：
SUBTYPE POSITIVE IS BINARY_INTEGER RANGE 1 .. 2147483647;
非限制型舉例：
SUBTYPE FLOAT IS NUMBER;
CREATE OR REPLACE PACKAGE utility
AS
SUBTYPE big_string IS VARCHAR2(32767);
SUBTYPE big_db_string IS VARCHAR2(4000);
END utility;

5.類型轉換
隱式轉換：pl/sql運行時引擎自動轉換
example:
有效的隱式轉換：
DECLARE
a_number NUMBER;
BEGIN
a_number := '125';
END;
以下隱式轉換將產生異常：
DECLARE
a_number NUMBER;
BEGIN
a_number := 'abc';
END;
隱式轉換的可轉換性表格：



顯示轉換：代碼中利用轉換函數執行轉換
example:
DECLARE
hd_display VARCHAR2 (30);
BEGIN
hd_display := CAST (SYSDATE AS VARCHAR2);
END;
類型轉換函數列表：
ASCIISTR，CAST，CHARTOROWID，CONVERT，FROM_TZ，HEXTORAW，MULTISET，NUMTODSINTERVAL，NUMTOYMINTERVAL，RAWTOHEX, RAWTONHEX，REFTOHEX，ROWIDTOCHAR, ROWIDTONCHAR，TABLE，THE，TO_BINARY_FLOAT，TO_BINARY_DOUBLE，TO_CHAR, TO_ NCHAR (number version)，TO_CHAR, TO_NCHAR (date version)，TO_CHAR, TO_NCHAR (character version)，TO_BLOB，TO_CLOB, TO_NCLOB，TO_DATE，TO_DSINTERVAL，TO_LOB，TO_MULTI_BYTE，TO_NUMBER，TO_RAW，TO_SINGLE_BYTE，TO_TIMESTAMP，TO_TIMESTAMP_TZ，TO_YMINTERVAL，TRANSLATE ... USING，UNISTR

CAST函數對個數據類型的可轉換性