MySQL: Syntax: Flag, keyword

The Character Sequence enclosed by backticks "'" is called a flag.

• If the ansi_quotes mode is enabled, you can use the Character Sequence enclosed by double quotation marks "" to represent the flag.
• The flag can contain any character,Of course, it is better to only use non-special characters such as [0-9a-za-z _ $,We recommend that you do not start with a number or dollar-this is the case for most systems.
• In addition, if the token is a keyword (usually equal to a reserved word), it must be included.
• The severe recommendation flag should not be "{m} e [N]", which may be confused with the scientific counting method!
• The flag cannot contain ascii nul (0x00), \,/,., NUL, PRN, and other operating systems.

The maximum character length of a flag is 64.

Flag restrictions:

• [Db_name.] [tb_name.] col_name -- MySQL Standard
• [.] Tb_name -- limits compatible with ODBC

 

The case sensitivity of the flag: It depends on OS: windows is not distinguished, Linux is differentiated

• Database, table, trigger, and alias depend on OS. But in the same statement, it must be exactly the same
• Column, index, procedure, funcion, and envent are not differentiated.

• Lower_case_table_names:

• 0: differentiate the size. Save, search, and compare. The MyISAM storage engine may cause index usage problems on some small and insensitive OS.
• 1: lower case. Save, search, and compare. -- Recommendation
• 2: case-sensitive OS storage; search and compare in lower case. However, the table of the InnoDB Storage engine class has the same behavior as "1 ".

 

Parsing rules for function names: one sentence (good programming style: not the same as what the system already has !!!)

• Generally, functions are divided into Native built-in, UDF, and stored functions.
• Native functions have default parsing rules, but they are related to the configuration of the ignore_space server.
• General rule: if a built-in function is followed by an express context, it is called as a function. Otherwise, it is considered as a flag and applies to most functions.
• Special rule: Check whether the function name is followed by "(", used as a function call, or not as a flag. You can use SQL _functions () to view these functions.

Ignore_space:

• Disabled: as long as it is a function listed in SQL _functions (), the above "Default rule" will be ignored, as long as it is followed by "(" is considered as a function call, it may cause non-expression environment errors
• Enabled: (default) as long as it is a function listed in SQL _functions (), it must contain the function name as a flag.