The definition section mainly defines variables and constants, and the syntax is as follows:
DECLARE
Virablename [CONSTANT] dataType [NOT null][:=|default exp or value];
The following guidelines should be followed when naming variables or constants:
1, variable name can only start the letter, other bits can contain _, $, #和数字
2, Length 1-30
3, case-insensitive
4, cannot be the system key word
The constant keyword represents the definition of a constant, which must be given an initial value, and the value cannot be changed again.
DataType is a data type, note that the data type here is the Pl/sql data type, not the SQL data type that the table uses.
Not NULL represents a variable or a constant is not allowed to be null, and must provide a Non-null initial value when defined.
The following code code defines variables and constants:
DECLARE
credit_limit CONSTANT NUMBER :=5000;--常量
invalid BOOLEAN := FALSE;--布尔类型变量
acct_id INTEGER(4) NOT NULL default 9999;--必须附初值的变量
pi CONSTANT REAL := 3.14159;--浮点数常量
postal_code VARCHAR2(20);--与VARCHAR2(20 BYTE)同义
last_name VARCHAR2(20 CHAR);--变量
my_ename emp.ename%TYPE;--与emp表的ename列数据类型相同
The Pl/sql data types are divided into four categories, scalar types, composite types, reference types, and LOB types.
One, scalar type
The meaning of a scalar type is that it holds a single value. The scalar types are divided into shaping, numbers, characters, dates, and Boolean types.
1, Binary_integer
The range is aninteger from -2 to--2, and if the floating-point number is assigned to the type, the floating-point number is rounded to the integer and then assigned to the type. In addition, there are several subtypes of the type:
NATURAL 0-2 range of integers
POSITIVE 1-2 range of integers
NATURALN does not allow null values, other same natural
Positiven does not allow null values, other same positive
Signtype symbol type, only three values allowed-1 0 13 values
Note: Binary_integer and its subtypes are pl/sql data types, not SQL data types, that is, they cannot be used when creating tables.