Chapter 9 Language Structure Table of Contents 9.1 Literal Values .......................................................................................................................... 1859 9.1.1 String Literals ............................................................................................................... 1859 9.1.2 Numeric Literals ........................................................................................................... 1862 9.1.3 Date and Time Literals ................................................................................................. 1862 9.1.4 Hexadecimal Literals .................................................................................................... 1865 9.1.5 Bit-Value Literals .......................................................................................................... 1867 9.1.6 Boolean Literals ........................................................................................................... 1868 9.1.7 NULL Values ............................................................................................................... 1869 9.2 Schema Object Names ........................................................................................................... 1869 9.2.1 Identifier Length Limits ................................................................................................. 1870 9.2.2 Identifier Qualifiers ....................................................................................................... 1871 9.2.3 Identifier Case Sensitivity ............................................................................................. 1873 9.2.4 Mapping of Identifiers to File Names ............................................................................. 1875 9.2.5 Function Name Parsing and Resolution ......................................................................... 1876 9.3 Keywords and Reserved Words .............................................................................................. 1880 9.4 User-Defined Variables ........................................................................................................... 1912 9.5 Expressions ............................................................................................................................ 1915 9.6 Query Attributes ...................................................................................................................... 1919 9.7 Comments .............................................................................................................................. 1922 This chapter discusses the rules for writing the following elements of SQL statements when using MySQL: This section describes how to write literal values in MySQL. These include strings, numbers, hexadecimal and bit values, boolean values, and  NULL . The section also covers various nuances that you may encounter when dealing with these basic types in MySQL. 9.1 Literal Values 9.1.1 String Literals •Comments •Query attributes •Expressions •User-defined and system variables •Keywords and reserved words •Identifiers such as database, table, and column names •Literal values such as strings and numbers A string is a sequence of bytes or characters, enclosed within either single quote ( ’ ) or double quote ( " ) characters. Examples: 1859 ’a string’ "another string"