Database schema:

CREATE TABLE customers (
	"CustomerID" INTEGER NOT NULL -- example: ['5', '3'],
	"Segment" TEXT -- client segment, example: ['LAM', 'SME'],
	"Currency" TEXT -- example: ['CZK', 'EUR'],
	PRIMARY KEY ("CustomerID"), 
	UNIQUE ("CustomerID")
)


CREATE TABLE gasstations (
	"GasStationID" INTEGER NOT NULL -- Gas Station ID, example: ['45', '44'],
	"ChainID" INTEGER -- Chain ID, example: ['6', '13'],
	"Country" TEXT -- example: ['CZE', 'SVK'],
	"Segment" TEXT -- chain segment, example: ['Value for money', 'Premium'],
	PRIMARY KEY ("GasStationID"), 
	UNIQUE ("GasStationID")
)


CREATE TABLE products (
	"ProductID" INTEGER NOT NULL -- Product ID, example: ['2', '1'],
	"Description" TEXT -- example: ['Rucní zadání', 'Nafta'],
	PRIMARY KEY ("ProductID"), 
	UNIQUE ("ProductID")
)


CREATE TABLE transactions_1k (
	"TransactionID" INTEGER -- Transaction ID, example: ['2', '1'],
	"Date" DATE -- example: ['2012-08-24', '2012-08-23'],
	"Time" TEXT -- example: ['09:41:00', '10:03:00'],
	"CustomerID" INTEGER -- Customer ID, example: ['31543', '46707'],
	"CardID" INTEGER -- Card ID, example: ['486621', '550134'],
	"GasStationID" INTEGER -- Gas Station ID, example: ['3704', '656'],
	"ProductID" INTEGER -- Product ID, example: ['2', '23'],
	"Amount" INTEGER -- example: ['28', '18'],
	"Price" REAL -- example: ['672.64', '430.72'],
	PRIMARY KEY ("TransactionID")
)


CREATE TABLE yearmonth (
	"CustomerID" INTEGER NOT NULL -- Customer ID, example: ['39', '63'],
	"Date" TEXT NOT NULL -- example: ['201201', '201112'],
	"Consumption" REAL -- example: ['1598.28', '528.3'],
	PRIMARY KEY ("Date", "CustomerID"), 
	CONSTRAINT fk_yearmonth_customers FOREIGN KEY("CustomerID") REFERENCES customers ("CustomerID")
)

Question: What is the difference in the annual average consumption of the customers with the least amount of consumption paid in CZK for 2013 between SME and LAM, LAM and KAM, and KAM and SME?
Evidence: annual average consumption of customer with the lowest consumption in each segment = total consumption per year / the number of customer with lowest consumption in each segment; Difference in annual average = SME's annual average - LAM's annual average; Difference in annual average = LAM's annual average - KAM's annual average; Year 2013 can be presented as Between 201301 And 201312; The first 4 strings of the Date values in the yearmonth table can represent year.

SQL:
SELECT CAST(SUM(IIF(T1.Segment = 'SME', T2.Consumption, 0)) AS REAL) / COUNT(T1.CustomerID) - CAST(SUM(IIF(T1.Segment = 'LAM', T2.Consumption, 0)) AS REAL) / COUNT(T1.CustomerID) , CAST(SUM(IIF(T1.Segment = 'LAM', T2.Consumption, 0)) AS REAL) / COUNT(T1.CustomerID) - CAST(SUM(IIF(T1.Segment = 'KAM', T2.Consumption, 0)) AS REAL) / COUNT(T1.CustomerID) , CAST(SUM(IIF(T1.Segment = 'KAM', T2.Consumption, 0)) AS REAL) / COUNT(T1.CustomerID) - CAST(SUM(IIF(T1.Segment = 'SME', T2.Consumption, 0)) AS REAL) / COUNT(T1.CustomerID) FROM customers AS T1 INNER JOIN yearmonth AS T2 ON T1.CustomerID = T2.CustomerID WHERE T1.Currency = 'CZK' AND T2.Consumption = ( SELECT MIN(Consumption) FROM yearmonth ) AND T2.Date BETWEEN 201301 AND 201312