Returns an evaluated expression value as an item.
EVAL "expression" [AS colname]
clause evaluates expression
and returns the result as a separate item. An expression
can be an expression involving numeric and string literals, variables, MVBasic functions, or field values. An expression
must be enclosed in double quotes. If expression
contains the name of a column, that column name is truncated to the first 50 characters.
An EVAL expression
that contains a field returns the contents of the field’s itype attribute. Note that in Caché MultiValue if the value of field
is a number, it is treated as a literal number and not an attribute name. For example, the itype expression "@DATE-1"
evaluates 1 as a numeric literal, and thus returns yesterday's date.
This evaluation of quoted numerics is consistent with most MultiValue implementation, with the exception of jBASE. jBASE evaluates a quoted number as an itype attribute name, and attempts to return the attribute contents.
LIST VOC "BASIC" "ASSOC" EVAL "@ID[1,3]"
It returns BAS and ASS.
You can specify multiple postfix operators. They are evaluated in the order specified. The following example uses two postfix operators. The first ([1,3]) extracts a substring consisting of the first 3 characters of the specified @ID values; the second ([2,99]) extracts a substring from that substring consisting of the second through 99th characters:
LIST VOC "BASIC" "ASSOC" EVAL "@ID[1,3][2,99]"
It returns AS and SS.
The number of sequential postfix operators is unlimited.
The optional AS clause lets you assign a column name to the resulting column. This colname
may be supplied with quote delimiters ("my text"
), which permits the column heading to contain blank spaces or other special characters. If no special characters are included, colname
delimiters are not required. Column headings are case-sensitive.
If you do not specify an AS clause, the expression
is used as the column header. The AS clause cannot specify a blank column heading. To display an EVAL
column with no column heading, use DISPLAY.NAME "\"
, instead of the AS keyword. To display a column heading that contains literal quote characters, use a DISPLAY.NAME
clause such as the following (DISPLAY.NAME \survey "yes" answers\
), instead of the AS keyword.
The following example evaluates an arithmetic operation on a variable value. EVAL
returns a date one week from the current date. It uses the AS clause to assign a name to this calculated date column:
LIST VOC WITH @ID LIKE Q... EVAL "@DATE+7" AS "Next Week"
VOC......... Next Week.
3 Items listed.
The following example uses EVAL
to specify a dictionary entry by position (rather than name) using the @RECORD variable. The following two statements are equivalent:
LIST VOC EVAL "@RECORD<4>" AS "Field4" WITH EVAL "@RECORD<4>"
LIST VOC F4 DISPLAY.NAME "Field4" WITH F4
Note the use of the AS keyword and the DISPLAY.NAME clause to assign a column heading to the specified field for each statement.
The following example uses EVAL
to return the length of each field’s @ID name, using the MVBasic SUBR
function to call the LENS (length) system function:
LIST VOC EVAL "SUBR('-LENS',@ID)" AS "NameLength"
© 1997-2019 InterSystems Corporation, Cambridge, MA