Oracle 5.0, Справочное руководство

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Chapter 9. Language Structure
Table of Contents
9.1. Literal Values ..................................................................................................................... 745
9.1.1. String Literals .......................................................................................................... 745
9.1.2. Number Literals ....................................................................................................... 747
9.1.3. Date and Time Literals ............................................................................................ 748
9.1.4. Hexadecimal Literals ................................................................................................ 750
9.1.5. Boolean Literals ....................................................................................................... 750
9.1.6. Bit-Field Literals ....................................................................................................... 750
9.1.7.
NULL
Values ........................................................................................................... 751
9.2. Schema Object Names ....................................................................................................... 751
9.2.1. Identifier Qualifiers ................................................................................................... 753
9.2.2. Identifier Case Sensitivity ......................................................................................... 754
9.2.3. Function Name Parsing and Resolution .................................................................... 755
9.3. Reserved Words ................................................................................................................ 758
9.4. User-Defined Variables ....................................................................................................... 761
9.5. Expression Syntax .............................................................................................................. 764
9.6. Comment Syntax ................................................................................................................ 766
This chapter discusses the rules for writing the following elements of SQL statements when using
MySQL:
• Literal values such as strings and numbers
• Identifiers such as database, table, and column names
• Reserved words
• User-defined and system variables
• Comments
9.1. Literal Values
This section describes how to write literal values in MySQL. These include strings, numbers,
hexadecimal values, boolean values, and
NULL
. The section also covers the various nuances and
“gotchas” that you may run into when dealing with these basic types in MySQL.
9.1.1. String Literals
A string is a sequence of bytes or characters, enclosed within either single quote (“
'
”) or double quote
(“
"
”) characters. Examples:
'a string'
"another string"
Quoted strings placed next to each other are concatenated to a single string. The following lines are
equivalent:
'a string'
'a' ' ' 'string'
If the
ANSI_QUOTES
[535] SQL mode is enabled, string literals can be quoted only within single
quotation marks because a string quoted within double quotation marks is interpreted as an identifier.