LAG (MDX)
Returned Type
This function returns a member.
Syntax and Details
member_expression.LAG(optional_integer_expression)
Where:
-
member_expression is an expression that returns a member.
This expression cannot refer to a measure.
-
optional_integer_expression is a nonnegative integer literal.
The default value for this argument is 0; in this case, the function returns the member given by member_expression.
If integer_expression is 1, this function is equivalent to the PREVMEMBER function.
This function examines the members of the level to which the given member belongs, counts backward from the current member (using integer_expression), and returns the member at that position. For time dimensions, this function ignores any parent level. For data dimensions, this function considers the parent level; it counts backward from the current member within the given parent member. (Note that the terms time dimension and data dimension refer specifically to the dimension type as defined in the cube. See Defining Models for InterSystems Business Intelligence.)
Within any time dimension, this function is more useful for a timeline-based time level (such as Period, which groups records by year and month) than for a date-part-based time level (such as Month, which groups records only by month). If the level is based on a date part, this function returns null when it refers to a level beyond the end of the set; see an example of a similar scenario in PREVMEMBER. For a fuller discussion, see Introduction to Time Levels.
Example
The first examples use a time dimension. Consider the following query, shown for reference:
SELECT MEASURES.[%COUNT] ON 0,
{birthd.1948,birthd.1949,birthd.1950,birthd.1951,birthd.1952} ON 1
FROM patients
Patient Count
1 1948 10
2 1949 4
3 1950 12
4 1951 8
5 1952 6
The following query uses LAG:
SELECT MEASURES.[%COUNT] ON 0, birthd.1951.LAG(1) ON 1 FROM patients
Patient Count
1950 12
For another example:
SELECT MEASURES.[%COUNT] ON 0, birthd.1951.LAG(2) ON 1 FROM patients
Patient Count
1949 4
In this sample, the year level is the child of the decade level, which means that the members 1949 and 1950 belong to different parents. As you can see, the LAG function ignores the parent level when you use the function with a time dimension.
The second examples use a data dimension (the HomeD dimension). To see the hierarchy in this dimension, see the examples in the FIRSTCHILD function. The following query uses LAG with this dimension:
SELECT MEASURES.[%COUNT] ON 0, homed.city.Magnolia.LAG(1) ON 1 FROM patients
Patient Count
Cypress 104
Because this is a data dimension, this query retrieves the previous member of the city level within the parent ZIP code. Within this ZIP code, Cypress is the first city, so the following query returns no results:
SELECT MEASURES.[%COUNT] ON 0, homed.city.Cypress.LAG(1) ON 1 FROM patients
Patient Count
*
