Link relative ratio refers to comparison between the current data and data of the previous period. The interval is usually one month. For example, divide sales amount of April by that of March, and you get the link relative ratio of April. Hour, day, week and quarter can also be used as the time interval. Year-on-year comparison is the comparison between the current data and data of the corresponding period of the previous year. For example, divide sales amount of April 2014 by that of April 2013. In business, data of multiple periods is usually computed to find the variation trend.

Seeking link relative ratio and year-on-year comparison is common inter-row and inter-group computations, which are easy to be performed with esProc. The following example is used to illustrate the computations.

**Case description:**

Compute link relative ratio and year-on-year comparison of each month’s sales amount within the designated period. The data comes from table order. Some of the data is shown below:

**esProc code:**

A1=esProc.query(“select * from sales3 where OrderDate>=? and OrderDate<=?”,begin,end)

A2=A1.groups(year(OrderDate):y,month(OrderDate):m;sum(Amount):mAmount)

A3=A2.derive(mAmount/mAmount[-1]:lrr)

A4=A3.sort(m)

A5=A4.derive(if(m==m[-1],mAmount/mAmount[-1],null):yoy)

**Code interpretation:**

A1: Query in the database according to periods.* begin* and *end* are external parameters. Such as, *begin=”2011-01-01 00:00:00″*, *end=”2014-07-08 00:00:00″*(i.e. the date of today which can be obtained through *now()* function). Some of the query results are as follows:

A2: Group orders by year and month, then summarize and seek each month’s sales amount. Some of the computed results are as follows:

A3: Add a new field *Irr*, i.e, the link relative ratio on a month-on-month basis. The code is *mAmount/mAmount[-1]*, in which *mAmount* represents sales amount of the current month, and *mAmount[-1]* represents that of the previous month. Note that the initial month’s link relative ratio is empty (i.e. January 2011). Computed results are:

A4: Sort A3 by month and year to compute year-on-year comparison. Complete code should be: *=A3.sort(m,y)*. Since A3 is originally sorted by the year, so we just need to sort by the month, the code is: *A3.sort(m)*, which has a higher performance. Some of the computed results are:

A5: A5: Add a new field *yoy*, i.e., theyear-on-year comparison of monthly sales amount. The code is: *if(m==m[-1],mAmount/mAmount[-1],null)*, meaning that the computation of year-on-year comparison is only performed over the corresponding months. Note that the year-on-year comparison for months of the initial year (i.e. the year 2011) is always. Some of the computed results are:

A row of code, *A6=A5.sort(y:-1,m)*, can be added to make observation easier. That is, sort A5 in descending year order and ascending month order. Note that the data comes to an end in July 2014. Results are shown below: