3 PL/SQL Data Types

Different Maximum Sizes

The SQL data types listed in Table 3-1 have different maximum sizes in PL/SQL and SQL.

^Footnote 1 When specifying the maximum size of a value of this data type in PL/SQL, use an integer literal (not a constant or variable) whose value is in the range from 1 through 32,767.

^Footnote 2 Supported only for backward compatibility with existing applications.

Additional PL/SQL Constants for BINARY_FLOAT and BINARY_DOUBLE

The SQL data types BINARY_FLOAT and BINARY_DOUBLE represent single-precision and double-precision IEEE 754-format floating-point numbers, respectively.

BINARY_FLOAT and BINARY_DOUBLE computations do not raise exceptions, so you must check the values that they produce for conditions such as overflow and underflow by comparing them to predefined constants (for examples, see Oracle Database SQL Language Reference). PL/SQL has more of these constants than SQL does.

Table 3-2 lists and describes the predefined PL/SQL constants for BINARY_FLOAT and BINARY_DOUBLE, and identifies those that SQL also defines.

^Footnote 1 SQL also predefines this constant.

Additional PL/SQL Subtypes of BINARY_FLOAT and BINARY_DOUBLE

PL/SQL predefines these subtypes:

• SIMPLE_FLOAT, a subtype of SQL data type BINARY_FLOAT

• SIMPLE_DOUBLE, a subtype of SQL data type BINARY_DOUBLE

Each subtype has the same range as its base type and has a NOT NULL constraint (explained in "NOT NULL Constraint").

If you know that a variable will never have the value NULL, declare it as SIMPLE_FLOAT or SIMPLE_DOUBLE, rather than BINARY_FLOAT or BINARY_DOUBLE. Without the overhead of checking for nullness, the subtypes provide significantly better performance than their base types. The performance improvement is greater with PLSQL_CODE_TYPE='NATIVE' than with PLSQL_CODE_TYPE='INTERPRETED' (for more information, see "Use Data Types that Use Hardware Arithmetic").

CHAR and VARCHAR2 Variables

Topics

• Assigning or Inserting Too-Long Values

• Declaring Variables for Multibyte Characters

• Differences Between CHAR and VARCHAR2 Data Types

DECLARE
  c VARCHAR2(3 CHAR);
BEGIN
  c := 'abc  ';
END;
/

DECLARE
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at line 4

DROP TABLE t;
CREATE TABLE t (c CHAR(3 CHAR));
 
DECLARE
  s VARCHAR2(5 CHAR) := 'abc  ';
BEGIN
  INSERT INTO t(c) VALUES(s);
END;
/

BEGIN
*
ERROR at line 1:
ORA-12899: value too large for column "HR"."T"."C" (actual: 5, maximum: 3)
ORA-06512: at line 4

DECLARE
  c VARCHAR2(3 CHAR);
BEGIN
  c := RTRIM('abc  ');
  INSERT INTO t(c) VALUES(RTRIM('abc  '));
END;
/

PL/SQL procedure successfully completed.

DECLARE
  first_name  CHAR(10 CHAR);
  last_name   VARCHAR2(10 CHAR);
BEGIN
  first_name := 'John ';
  last_name  := 'Chen ';
 
  DBMS_OUTPUT.PUT_LINE('*' || first_name || '*');
  DBMS_OUTPUT.PUT_LINE('*' || last_name || '*');
END;
/

*John      *
*Chen *

LONG and LONG RAW Variables

You can insert any LONG value into a LONG column. You can insert any LONG RAW value into a LONG RAW column. You cannot retrieve a value longer than 32,760 bytes from a LONG or LONG RAW column into a LONG or LONG RAW variable.

You can insert any CHAR or VARCHAR2 value into a LONG column. You cannot retrieve a value longer than 32,767 bytes from a LONG column into a CHAR or VARCHAR2 variable.

You can insert any RAW value into a LONG RAW column. You cannot retrieve a value longer than 32,767 bytes from a LONG RAW column into a RAW variable.

ROWID and UROWID Variables

When you retrieve a rowid into a ROWID variable, use the ROWIDTOCHAR function to convert the binary value to a character value. For information about this function, see Oracle Database SQL Language Reference.

To convert the value of a ROWID variable to a rowid, use the CHARTOROWID function, explained in Oracle Database SQL Language Reference. If the value does not represent a valid rowid, PL/SQL raises the predefined exception SYS_INVALID_ROWID.

To retrieve a rowid into a UROWID variable, or to convert the value of a UROWID variable to a rowid, use an assignment statement; conversion is implicit.

Preventing PLS_INTEGER Overflow

A calculation with two PLS_INTEGER values that overflows the PLS_INTEGER range raises an overflow exception, even if you assign the result to a NUMBER data type (as in Example 3-3). For calculations outside the PLS_INTEGER range, use INTEGER, a predefined subtype of the NUMBER data type (as in Example 3-4).

DECLARE
  p1 PLS_INTEGER := 2147483647;
  p2 PLS_INTEGER := 1;
  n NUMBER;
BEGIN
  n := p1 + p2;
END;
/

DECLARE
*
ERROR at line 1:
ORA-01426: numeric overflow
ORA-06512: at line 6

DECLARE
  p1 PLS_INTEGER := 2147483647;
  p2 INTEGER := 1;
  n NUMBER;
BEGIN
  n := p1 + p2;
END;
/

PL/SQL procedure successfully completed.

Predefined PLS_INTEGER Subtypes

Table 3-3 lists the predefined subtypes of the PLS_INTEGER data type and describes the data they store.

^Footnote 1 For information about the NOT NULL constraint, see "NOT NULL Constraint".

PLS_INTEGER and its subtypes can be implicitly converted to these data types:

• CHAR

• VARCHAR2

• NUMBER

• LONG

All of the preceding data types except LONG, and all PLS_INTEGER subtypes, can be implicitly converted to PLS_INTEGER.

A PLS_INTEGER value can be implicitly converted to a PLS_INTEGER subtype only if the value does not violate a constraint of the subtype. For example, casting the PLS_INTEGER value NULL to the SIMPLE_INTEGER subtype raises an exception, as Example 3-5 shows.

DECLARE
  a SIMPLE_INTEGER := 1;
  b PLS_INTEGER := NULL;
BEGIN
  a := b;
END;
/

DECLARE
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error
ORA-06512: at line 5

SIMPLE_INTEGER Subtype of PLS_INTEGER

SIMPLE_INTEGER is a predefined subtype of the PLS_INTEGER data type that has the same range as PLS_INTEGER and has a NOT NULL constraint (explained in "NOT NULL Constraint"). It differs significantly from PLS_INTEGER in its overflow semantics.

If you know that a variable will never have the value NULL or need overflow checking, declare it as SIMPLE_INTEGER rather than PLS_INTEGER. Without the overhead of checking for nullness and overflow, SIMPLE_INTEGER performs significantly better than PLS_INTEGER.

Topics

• SIMPLE_INTEGER Overflow Semantics

• Expressions with Both SIMPLE_INTEGER and Other Operands

• Integer Literals in SIMPLE_INTEGER Range

DECLARE
  n SIMPLE_INTEGER := 2147483645;
BEGIN
  FOR j IN 1..4 LOOP
    n := n + 1;
    DBMS_OUTPUT.PUT_LINE(TO_CHAR(n, 'S9999999999'));
  END LOOP;
  FOR j IN 1..4 LOOP
   n := n - 1;
   DBMS_OUTPUT.PUT_LINE(TO_CHAR(n, 'S9999999999'));
  END LOOP;
END;
/

+2147483646
+2147483647
-2147483648
-2147483647
-2147483648
+2147483647
+2147483646
+2147483645

PL/SQL procedure successfully completed.

Unconstrained Subtypes

An unconstrained subtype has the same set of values as its base type, so it is only another name for the base type. Therefore, unconstrained subtypes of the same base type are interchangeable with each other and with the base type. No data type conversion occurs.

To define an unconstrained subtype, use this syntax:

SUBTYPE subtype_name IS base_type

For information about subtype_name and base_type, see subtype_definition.

An example of an unconstrained subtype, which PL/SQL predefines for compatibility with ANSI, is:

SUBTYPE "DOUBLE PRECISION" IS FLOAT

In Example 3-6, the unconstrained subtypes Balance and Counter show the intended uses of data items of their types.

DECLARE
  SUBTYPE Balance IS NUMBER;

  checking_account        Balance(6,2);
  savings_account         Balance(8,2);
  certificate_of_deposit  Balance(8,2);
  max_insured  CONSTANT   Balance(8,2) := 250000.00;

  SUBTYPE Counter IS NATURAL;

  accounts     Counter := 1;
  deposits     Counter := 0;
  withdrawals  Counter := 0;
  overdrafts   Counter := 0;

  PROCEDURE deposit (
    account  IN OUT Balance,
    amount   IN     Balance
  ) IS
  BEGIN
    account  := account + amount;
    deposits := deposits + 1;
  END;
  
BEGIN
  NULL;
END;
/

Constrained Subtypes

A constrained subtype has only a subset of the values of its base type.

If the base type lets you specify size, precision and scale, or a range of values, then you can specify them for its subtypes. The subtype definition syntax is:

SUBTYPE subtype_name IS base_type
  { precision [, scale ] | RANGE low_value .. high_value } [ NOT NULL ]

Otherwise, the only constraint that you can put on its subtypes is NOT NULL (described in "NOT NULL Constraint"):

SUBTYPE subtype_name IS base_type [ NOT NULL ]

In Example 3-7, the constrained subtype Balance detects out-of-range values.

DECLARE
  SUBTYPE Balance IS NUMBER(8,2);
 
  checking_account  Balance;
  savings_account   Balance;
 
BEGIN
  checking_account := 2000.00;
  savings_account  := 1000000.00;
END;
/

DECLARE
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: number precision too large
ORA-06512: at line 9

A constrained subtype can be implicitly converted to its base type, but the base type can be implicitly converted to the constrained subtype only if the value does not violate a constraint of the subtype (see Example 3-5).

A constrained subtype can be implicitly converted to another constrained subtype with the same base type only if the source value does not violate a constraint of the target subtype.

In Example 3-8, the three constrained subtypes have the same base type. The first two subtypes can be implicitly converted to the third subtype, but not to each other.

DECLARE
  SUBTYPE Digit        IS PLS_INTEGER RANGE 0..9;
  SUBTYPE Double_digit IS PLS_INTEGER RANGE 10..99;
  SUBTYPE Under_100    IS PLS_INTEGER RANGE 0..99;
 
  d   Digit        :=  4;
  dd  Double_digit := 35;
  u   Under_100;
BEGIN
  u := d;   -- Succeeds; Under_100 range includes Digit range
  u := dd;  -- Succeeds; Under_100 range includes Double_digit range
  dd := d;  -- Raises error; Double_digit range does not include Digit range
END;
/

DECLARE
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error
ORA-06512: at line 12

Subtypes with Base Types in Same Data Type Family

If two subtypes have different base types in the same data type family, then one subtype can be implicitly converted to the other only if the source value does not violate a constraint of the target subtype. (For the predefined PL/SQL data types and subtypes, grouped by data type family, see Appendix E, "PL/SQL Predefined Data Types".)

In Example 3-9, the subtypes Word and Text have different base types in the same data type family. The first assignment statement implicitly converts a Word value to Text. The second assignment statement implicitly converts a Text value to Word. The third assignment statement cannot implicitly convert the Text value to Word, because the value is too long.

DECLARE
  SUBTYPE Word IS CHAR(6);
  SUBTYPE Text IS VARCHAR2(15);
 
  verb       Word := 'run';
  sentence1  Text;
  sentence2  Text := 'Hurry!';
  sentence3  Text := 'See Tom run.';
 
BEGIN
  sentence1 := verb;  -- 3-character value, 15-character limit
  verb := sentence2;  -- 5-character value, 6-character limit
  verb := sentence3;  -- 12-character value, 6-character limit
END;
/

DECLARE
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at line 13