A Collection of Database Help Functions

Datatbase Helper Functions

A collection of database related functions

Function	Code	Description
keys	@keys(x)	Return key
values	@values(x)	Return value
meta	@meta(x)	Return meta information
fetch	@fetch(x)	Fetch actual value
column_value	@column_value(x, n)	Load the column 'n' from the table 'x'
load_table	@load_table(n)	Load a table 'n'

keys

Description

• Return the key value of a variable with a compound type

Type Rules

dict   -> Any
enum   -> Any
table  -> sym
ktable -> table
_      -> domain error

values

Description

• Return the value of a variable with a compound type
• For enumeration, it returns the stored indices which have the type i64

Type Rules

dict   -> Any
enum   -> i64
table  -> list
ktable -> table
_      -> domain error

fetch

Description

• Return the actual value stored in an enumeration

Type Rules

enum<T> -> T
_       -> domain error

meta

Description

• Show a keyed table which represents the meta information of a table or a keyed table

Type Rules

table  -> ktable
ktable -> ktable
_      -> domain error

Examples

    // Table D
sym  price hq
-------------
appl 449.1 CA
ibm  108.2 NY
hp   24.5  CA
goog 890.3 CA

    // meta(D)
c    | t f a
-----|------
sym  | S    
price| E    
hq   | C    

where,

• c means column names;
• t means column types;
• f means the names of tables with foreign keys;
• a means column attributes.

column_value

Description

• Load the column value by a given column name

Type Rules

table  , sym -> Basic or enum
ktable , sym -> Basic or enum
_      , _   -> domain error

load_table

Description

• Load a table from memory by a given table name

Type Rules

sym -> table or ktable
 _  -> domain error