Basic datatypes - deep understanding
- 2. Liron Amitzi Oracle DBA since 1998 (and Oracle 7) Database consultant since 2002 Oracle ACE An independent senior DB consultant Recently moved to Vancouver, BC BCOUG president
- 3. 3 Membership Tiers • Oracle ACE Director • Oracle ACE • Oracle ACE Associate bit.ly/OracleACEProgram 500+ Technical Experts Helping Peers Globally Connect: Nominate yourself or someone you know: acenomination.oracle.com @oracleace Facebook.com/oracleaces oracle-ace_ww@oracle.com
- 4. Basic datatypes are the standard datatypes we use for table columns: CHAR VARCHAR2 NUMBER DATE In this session we will get to know them better, much better…
- 5. Fixed datatypes ◦ CHAR (1-2000 bytes) ◦ DATE (7 byte) ◦ TIMESTAMP (7-11 bytes) WITH TIME ZONE (13 bytes) ◦ ROWID (10 bytes) Variable datatypes ◦ NUMBER (1-22 bytes) ◦ VARCHAR2 (1-4000 bytes, 1-32767 bytes in 12c with MAX_STRING_SIZE=EXTENDED)
- 6. The physical structure of every value consists of three parts: • Type number – One byte that represents the type of the value (for example, 1 is VARCHAR2, 2 is NUMBER and 96 is CHAR) ◦ Length – One or two bytes that represent the size of the value ◦ Value data – The data itself
- 7. To check the real structure of datatypes we will use: Vsize – returns the real size the value takes (excluding length bytes) select vsize('abc') from dual => 3 Dump – returns the real binary value of the data (converted to decimal) select dump('abc') from dual => Typ=96 Len=3: 97,98,99
- 8. “Variable size” – takes the actual space needed VARCHAR2(x) means the value is limited to x (bytes or characters) VARCHAR is currently a synonym for VARCHAR2 but might be scheduled to be used for different purposes Maximum size is 4000 bytes (<12c)
- 9. New since 12c STANDARD ◦ Limit of 4000 for VARCHAR2 and NVARCHAR2 ◦ Limit of 2000 for RAW EXTENDED - cannot be changed back ◦ Limit VARCHAR2, NVARCHAR2 and RAW to 32767 When exceeds 4000 bytes, it is stored out of line (LOB)
- 10. "Fixed size” - CHAR(x): value will take x (bytes or chars) Padded with spaces Can be queried without spaces 2000 bytes max (regardless MAX_STRING_SIZE) Internally identical to VARCHAR2 Oracle still saves the length bytes - any ideas why? No performance improvements over VARCHAR2
- 11. "The only time I personally use a CHAR type is for CHAR(1). And that is only because its faster to type char(1) then varchar2(1). It offers no advantages." Tom Kyte on AskTom Demo - char.sql
- 12. Single character set - multiple languages and symbols Up to 3 bytes per character in UTF8 Up to 4 bytes per character in AL32UTF8 or AL16UTF16 The hard limits are: ◦ VARCHAR2 (MAX_STRING_SIZE=STANDARD or <12c): 4000 bytes ◦ VARCHAR2 (MAX_STRING_SIZE=EXTENDED): 32767 bytes ◦ CHAR: 2000 bytes More on Unicode character sets in note 260893.1
- 13. Relevant for multi-byte character sets Default text length limitation Value can be BYTE or CHAR (default is BYTE) Can limit max column size when creating a table: CREATE TABLE mytab ( f1 CHAR(4 byte), -- > max of 4 bytes (1-4 characters) f2 CHAR(4 char), -- > max of 4 chars (1-16 bytes) f3 CHAR(4)) -- > depends on NLS_LENGTH_SEMANTICS Demo - unicode.sql
- 14. “Fixed size” datatype, takes 7 bytes: ◦ 1st and 2nd bytes are century and year (excess 100 notation) ◦ 3rd and 4th bytes are month and day ◦ 5th – 7th bytes are hours, minutes and seconds, excess 1 notation
- 15. If no year, month, or day entered, the default is the first day of the current month If no hour, minutes, seconds entered, the default is zero All arithmetic operations on dates are in days More about representation of DATE in note 69028.1 Demo - date.sql
- 16. Variable size datatype NOT programing language number types The first bit in the first byte is the sign, the other 7 are the exponent (excess 64) All other bytes are the number in base 100 format (every 2 digits are a single byte), excess 1
- 17. Trailing zeros do not consume space Range is 1.0 x 10-130 to but not including 1.0 x 10126 More about representation of NUMBER in note 1031902.6 Demo - number.sql
- 18. NUMBER datatype is NOT native to the hardware Is it faster than CHAR/VARCHAR2? NO Needs processing as well In most cases, NUMBER columns will not be sorted much quicker than VARCHAR2 columns Demo - sort.sql
- 19. If we have time
- 20. When using PL/SQL we have the PLS_INTEGER datatype PLS_INTEGER is native to the hardware In SQL and database tables, PLS_INTEGER is converted to regular NUMBER Using PLS_INTEGER for variables that need many calculations can improve performance Demo - PLSQL.sql