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